[PATCH v4 0/8] iio: add new backend framework

[PATCH v4 0/8] iio: add new backend framework

[Nuno Sa]

v1:
 https://lore.kernel.org/linux-iio/20231204144925.4fe9922f@jic23-huawei/T/#m222f5175273b81dbfe40b7f0daffcdc67d6cb8ff

v2:
 https://lore.kernel.org/r/20231208-dev-iio-backend-v2-0-5450951895e1@analog.com

v3:
 https://lore.kernel.org/linux-iio/20231213-dev-iio-backend-v3-0-bb9f12a5c6dc@analog.com/

Changes in v4:
 - Patch 1:
  * Don't make io-backends mandatory.
- Patch 5:
  * Add helper __devm_iio_backend_get();
  * Add new devm_iio_backend_get_optional();
  * Add new devm_iio_backend_get_from_fwnode_lookup();
  * Convert all dev_ logs to plain pr_ logs so we actually use pr_fmt.
- Patch 6:
  * Implement the fallback backend lookput in case
    devm_iio_backend_get_optional() fails;

So the main difference in this series is to still handle 'adi,adc-dev'
in case 'io-backends' is not given. Hence we don't need to make it
mandatory and break dt ABI for the ad9467 bindings. Rob, it would be
nice if you can take a quick a look on it and let me know if there's a
more efficient way of doing things.

Rob also already expressed that he is ok with the dt ABI breakage as long
as it is properly justified in the commit message. Jonathan, we should
see if we keep things as in this version or rollback. Personally I'm not
that "happy" with that devm_iio_backend_get_from_fwnode_lookup() given
the fact that is not really supposed to be used anymore. OTOH, it's small
and simple... So, let me know your preference and I'll go with that :).

This is likely the last version of this series for this year. If things
go well, I plan to start working on the second user of the framework
right in the beginning of the next year...
 
Keeping the block diagram in v3's cover so we don't have to follow links
to check one of the typical setups. 

                                           -------------------------------------------------------
 ------------------                        | -----------         ------------      -------  FPGA |
 |     ADC        |------------------------| | AXI ADC |---------| DMA CORE |------| RAM |       |
 | (Frontend/IIO) | Serial Data (eg: LVDS) | |(backend)|---------|          |------|     |       |
 |                |------------------------| -----------         ------------      -------       |
 ------------------                        -------------------------------------------------------

---
Nuno Sa (7):
      dt-bindings: adc: ad9467: add new io-backend property
      dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'
      driver: core: allow modifying device_links flags
      iio: buffer-dmaengine: export buffer alloc and free functions
      iio: add the IIO backend framework
      iio: adc: ad9467: convert to backend framework
      iio: adc: adi-axi-adc: move to backend framework

Olivier Moysan (1):
      of: property: add device link support for io-backends

 .../devicetree/bindings/iio/adc/adi,ad9467.yaml    |   4 +
 .../devicetree/bindings/iio/adc/adi,axi-adc.yaml   |   4 +-
 MAINTAINERS                                        |   8 +
 drivers/base/core.c                                |  14 +-
 drivers/iio/Kconfig                                |   5 +
 drivers/iio/Makefile                               |   1 +
 drivers/iio/adc/Kconfig                            |   4 +-
 drivers/iio/adc/ad9467.c                           | 282 ++++++++-----
 drivers/iio/adc/adi-axi-adc.c                      | 381 +++++------------
 drivers/iio/buffer/industrialio-buffer-dmaengine.c |   8 +-
 drivers/iio/industrialio-backend.c                 | 456 +++++++++++++++++++++
 drivers/of/property.c                              |   2 +
 include/linux/iio/adc/adi-axi-adc.h                |  68 ---
 include/linux/iio/backend.h                        |  75 ++++
 include/linux/iio/buffer-dmaengine.h               |   3 +
 15 files changed, 845 insertions(+), 470 deletions(-)
---
base-commit: 2dfef50589aef3b9a2fa2190ae95b328fb664f89
change-id: 20231219-iio-backend-a3dc1a6a7a58
--

Thanks!
- Nuno Sá

[PATCH v4 1/8] dt-bindings: adc: ad9467: add new io-backend property

[Nuno Sa]

The ad9467 will make use of the new IIO backend framework which is a
provider - consumer interface where IIO backends provide services to
consumers. As such, and being this device a consumer,  add the new
generic io-backend property to the bindings.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml b/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
index 7aa748d6b7a0..eecd5fbab695 100644
--- a/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml
@@ -44,6 +44,9 @@ properties:
       Pin that controls the powerdown mode of the device.
     maxItems: 1
 
+  io-backends:
+    maxItems: 1
+
   reset-gpios:
     description:
       Reset pin for the device.
@@ -68,6 +71,7 @@ examples:
             reg = <0>;
             clocks = <&adc_clk>;
             clock-names = "adc-clk";
+            io-backends = <&iio_backend>;
         };
     };
 ...

-- 
2.43.0

[PATCH v4 2/8] dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'

[Nuno Sa]

'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
also remove it from being required.

The reason why it's being deprecated is because the axi-adc CORE is now
an IIO service provider hardware (IIO backends) for consumers to make use
of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
of consumer referencing other nodes/devices) and that proved to be wrong
and to not scale.

Now, IIO consumers of this hardware are expected to reference it using the
io-backends property.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
index 9996dd93f84b..835b40063343 100644
--- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
+++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
@@ -39,12 +39,12 @@ properties:
     $ref: /schemas/types.yaml#/definitions/phandle
     description:
       A reference to a the actual ADC to which this FPGA ADC interfaces to.
+    deprecated: true
 
 required:
   - compatible
   - dmas
   - reg
-  - adi,adc-dev
 
 additionalProperties: false
 
@@ -55,7 +55,5 @@ examples:
         reg = <0x44a00000 0x10000>;
         dmas = <&rx_dma 0>;
         dma-names = "rx";
-
-        adi,adc-dev = <&spi_adc>;
     };
 ...

-- 
2.43.0

[PATCH v4 3/8] driver: core: allow modifying device_links flags

[Nuno Sa]

If a device_link is previously created (eg: via
fw_devlink_create_devlink()) before the supplier + consumer are both
present and bound to their respective drivers, there's no way to set
DL_FLAG_AUTOREMOVE_CONSUMER anymore while one can still set
DL_FLAG_AUTOREMOVE_SUPPLIER. Hence, rework the flags checks to allow
for DL_FLAG_AUTOREMOVE_CONSUMER in the same way
DL_FLAG_AUTOREMOVE_SUPPLIER is done.

While at it, make sure that we are never left with
DL_FLAG_AUTOPROBE_CONSUMER set together with one of
DL_FLAG_AUTOREMOVE_CONSUMER or DL_FLAG_AUTOREMOVE_SUPPLIER.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/base/core.c | 14 +++++++++-----
 1 file changed, 9 insertions(+), 5 deletions(-)

diff --git a/drivers/base/core.c b/drivers/base/core.c
index 67ba592afc77..fdbb5abc75d5 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -807,11 +807,15 @@ struct device_link *device_link_add(struct device *consumer,
 		 * update the existing link to stay around longer.
 		 */
 		if (flags & DL_FLAG_AUTOREMOVE_SUPPLIER) {
-			if (link->flags & DL_FLAG_AUTOREMOVE_CONSUMER) {
-				link->flags &= ~DL_FLAG_AUTOREMOVE_CONSUMER;
-				link->flags |= DL_FLAG_AUTOREMOVE_SUPPLIER;
-			}
-		} else if (!(flags & DL_FLAG_AUTOREMOVE_CONSUMER)) {
+			link->flags &= ~DL_FLAG_AUTOREMOVE_CONSUMER;
+			link->flags &= ~DL_FLAG_AUTOPROBE_CONSUMER;
+			link->flags |= DL_FLAG_AUTOREMOVE_SUPPLIER;
+
+		} else if (flags & DL_FLAG_AUTOREMOVE_CONSUMER) {
+			link->flags &= ~DL_FLAG_AUTOREMOVE_SUPPLIER;
+			link->flags &= ~DL_FLAG_AUTOPROBE_CONSUMER;
+			link->flags |= DL_FLAG_AUTOREMOVE_CONSUMER;
+		} else {
 			link->flags &= ~(DL_FLAG_AUTOREMOVE_CONSUMER |
 					 DL_FLAG_AUTOREMOVE_SUPPLIER);
 		}

-- 
2.43.0

[PATCH v4 4/8] of: property: add device link support for io-backends

[Nuno Sa]

From: Olivier Moysan <olivier.moysan@foss.st.com>

Add support for creating device links out of more DT properties.

Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/of/property.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/of/property.c b/drivers/of/property.c
index afdaefbd03f6..a4835447759f 100644
--- a/drivers/of/property.c
+++ b/drivers/of/property.c
@@ -1244,6 +1244,7 @@ DEFINE_SIMPLE_PROP(interconnects, "interconnects", "#interconnect-cells")
 DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
 DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
 DEFINE_SIMPLE_PROP(io_channels, "io-channel", "#io-channel-cells")
+DEFINE_SIMPLE_PROP(io_backends, "io-backends", NULL)
 DEFINE_SIMPLE_PROP(interrupt_parent, "interrupt-parent", NULL)
 DEFINE_SIMPLE_PROP(dmas, "dmas", "#dma-cells")
 DEFINE_SIMPLE_PROP(power_domains, "power-domains", "#power-domain-cells")
@@ -1334,6 +1335,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
 	{ .parse_prop = parse_iommu_maps, .optional = true, },
 	{ .parse_prop = parse_mboxes, },
 	{ .parse_prop = parse_io_channels, },
+	{ .parse_prop = parse_io_backends, },
 	{ .parse_prop = parse_interrupt_parent, },
 	{ .parse_prop = parse_dmas, .optional = true, },
 	{ .parse_prop = parse_power_domains, },

-- 
2.43.0

[PATCH v4 5/8] iio: buffer-dmaengine: export buffer alloc and free functions

[Nuno Sa]

Export iio_dmaengine_buffer_free() and iio_dmaengine_buffer_alloc().
This is in preparation of introducing IIO backends support. This will
allow us to allocate a buffer and control it's lifetime from a device
different from the one holding the DMA firmware properties. Effectively,
in this case the struct device holding the firmware information about
the DMA channels is not the same as iio_dev->dev.parent (typical case).

While at it, namespace the buffer-dmaengine exports and update the
current user of these buffers.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/adi-axi-adc.c                      | 1 +
 drivers/iio/buffer/industrialio-buffer-dmaengine.c | 8 +++++---
 include/linux/iio/buffer-dmaengine.h               | 3 +++
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
index c247ff1541d2..0f21d1d98b9f 100644
--- a/drivers/iio/adc/adi-axi-adc.c
+++ b/drivers/iio/adc/adi-axi-adc.c
@@ -447,3 +447,4 @@ module_platform_driver(adi_axi_adc_driver);
 MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices Generic AXI ADC IP core driver");
 MODULE_LICENSE("GPL v2");
+MODULE_IMPORT_NS(IIO_DMAENGINE_BUFFER);
diff --git a/drivers/iio/buffer/industrialio-buffer-dmaengine.c b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
index 5f85ba38e6f6..0d53c0a07b0d 100644
--- a/drivers/iio/buffer/industrialio-buffer-dmaengine.c
+++ b/drivers/iio/buffer/industrialio-buffer-dmaengine.c
@@ -159,7 +159,7 @@ static const struct iio_dev_attr *iio_dmaengine_buffer_attrs[] = {
  * Once done using the buffer iio_dmaengine_buffer_free() should be used to
  * release it.
  */
-static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	const char *channel)
 {
 	struct dmaengine_buffer *dmaengine_buffer;
@@ -210,6 +210,7 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
 	kfree(dmaengine_buffer);
 	return ERR_PTR(ret);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_alloc, IIO_DMAENGINE_BUFFER);
 
 /**
  * iio_dmaengine_buffer_free() - Free dmaengine buffer
@@ -217,7 +218,7 @@ static struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
  *
  * Frees a buffer previously allocated with iio_dmaengine_buffer_alloc().
  */
-static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 {
 	struct dmaengine_buffer *dmaengine_buffer =
 		iio_buffer_to_dmaengine_buffer(buffer);
@@ -227,6 +228,7 @@ static void iio_dmaengine_buffer_free(struct iio_buffer *buffer)
 
 	iio_buffer_put(buffer);
 }
+EXPORT_SYMBOL_NS_GPL(iio_dmaengine_buffer_free, IIO_DMAENGINE_BUFFER);
 
 static void __devm_iio_dmaengine_buffer_free(void *buffer)
 {
@@ -288,7 +290,7 @@ int devm_iio_dmaengine_buffer_setup(struct device *dev,
 
 	return iio_device_attach_buffer(indio_dev, buffer);
 }
-EXPORT_SYMBOL_GPL(devm_iio_dmaengine_buffer_setup);
+EXPORT_SYMBOL_NS_GPL(devm_iio_dmaengine_buffer_setup, IIO_DMAENGINE_BUFFER);
 
 MODULE_AUTHOR("Lars-Peter Clausen <lars@metafoo.de>");
 MODULE_DESCRIPTION("DMA buffer for the IIO framework");
diff --git a/include/linux/iio/buffer-dmaengine.h b/include/linux/iio/buffer-dmaengine.h
index 5c355be89814..cbb8ba957fad 100644
--- a/include/linux/iio/buffer-dmaengine.h
+++ b/include/linux/iio/buffer-dmaengine.h
@@ -10,6 +10,9 @@
 struct iio_dev;
 struct device;
 
+struct iio_buffer *iio_dmaengine_buffer_alloc(struct device *dev,
+					      const char *channel);
+void iio_dmaengine_buffer_free(struct iio_buffer *buffer);
 int devm_iio_dmaengine_buffer_setup(struct device *dev,
 				    struct iio_dev *indio_dev,
 				    const char *channel);

-- 
2.43.0

[PATCH v4 6/8] iio: add the IIO backend framework

[Nuno Sa]

This is a Framework to handle complex IIO aggregate devices.

The typical architecture is to have one device as the frontend device which
can be "linked" against one or multiple backend devices. All the IIO and
userspace interface is expected to be registers/managed by the frontend
device which will callback into the backends when needed (to get/set
some configuration that it does not directly control).

The basic framework interface is pretty simple:
 - Backends should register themselves with @devm_iio_backend_register()
 - Frontend devices should get backends with @devm_iio_backend_get()

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 MAINTAINERS                        |   8 +
 drivers/iio/Kconfig                |   5 +
 drivers/iio/Makefile               |   1 +
 drivers/iio/industrialio-backend.c | 456 +++++++++++++++++++++++++++++++++++++
 include/linux/iio/backend.h        |  75 ++++++
 5 files changed, 545 insertions(+)

diff --git a/MAINTAINERS b/MAINTAINERS
index 3029841e92a8..df5f5b988926 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -10334,6 +10334,14 @@ L:	linux-media@vger.kernel.org
 S:	Maintained
 F:	drivers/media/rc/iguanair.c
 
+IIO BACKEND FRAMEWORK
+M:	Nuno Sa <nuno.sa@analog.com>
+R:	Olivier Moysan <olivier.moysan@foss.st.com>
+L:	linux-iio@vger.kernel.org
+S:	Maintained
+F:	drivers/iio/industrialio-backend.c
+F:	include/linux/iio/backend.h
+
 IIO DIGITAL POTENTIOMETER DAC
 M:	Peter Rosin <peda@axentia.se>
 L:	linux-iio@vger.kernel.org
diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
index 52eb46ef84c1..451671112f73 100644
--- a/drivers/iio/Kconfig
+++ b/drivers/iio/Kconfig
@@ -71,6 +71,11 @@ config IIO_TRIGGERED_EVENT
 	help
 	  Provides helper functions for setting up triggered events.
 
+config IIO_BACKEND
+	tristate
+	help
+	  Framework to handle complex IIO aggregate devices.
+
 source "drivers/iio/accel/Kconfig"
 source "drivers/iio/adc/Kconfig"
 source "drivers/iio/addac/Kconfig"
diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
index 9622347a1c1b..0ba0e1521ba4 100644
--- a/drivers/iio/Makefile
+++ b/drivers/iio/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o
 obj-$(CONFIG_IIO_SW_DEVICE) += industrialio-sw-device.o
 obj-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
 obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
+obj-$(CONFIG_IIO_BACKEND) += industrialio-backend.o
 
 obj-y += accel/
 obj-y += adc/
diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
new file mode 100644
index 000000000000..75a0a66003e1
--- /dev/null
+++ b/drivers/iio/industrialio-backend.c
@@ -0,0 +1,456 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Framework to handle complex IIO aggregate devices.
+ *
+ * The typical architecture is to have one device as the frontend device which
+ * can be "linked" against one or multiple backend devices. All the IIO and
+ * userspace interface is expected to be registers/managed by the frontend
+ * device which will callback into the backends when needed (to get/set some
+ * configuration that it does not directly control).
+ *
+ * The framework interface is pretty simple:
+ *   - Backends should register themselves with @devm_iio_backend_register()
+ *   - Frontend devices should get backends with @devm_iio_backend_get()
+ *
+ * Also to note that the primary target for this framework are converters like
+ * ADC/DACs so @iio_backend_ops will have some operations typical of converter
+ * devices. On top of that, this is "generic" for all IIO which means any kind
+ * of device can make use of the framework. That said, If the @iio_backend_ops
+ * struct begins to grow out of control, we can always refactor things so that
+ * the industrialio-backend.c is only left with the really generic stuff. Then,
+ * we can build on top of it depending on the needs.
+ *
+ * Copyright (C) 2023 Analog Devices Inc.
+ */
+#define pr_fmt(fmt) "iio-backend: " fmt
+
+#include <linux/cleanup.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/list.h>
+#include <linux/lockdep.h>
+#include <linux/kref.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/slab.h>
+
+#include <linux/iio/backend.h>
+
+struct iio_backend {
+	struct list_head entry;
+	const struct iio_backend_ops *ops;
+	struct device *dev;
+	struct module *owner;
+	void *priv;
+	/*
+	 * mutex used to synchronize backend callback access with concurrent
+	 * calls to @iio_backend_unregister. The lock makes sure a device is
+	 * not unregistered while a callback is being run.
+	 */
+	struct mutex lock;
+	struct kref ref;
+};
+
+/*
+ * Helper struct for requesting buffers. Allows for multiple buffers per
+ * backend.
+ */
+struct iio_backend_buffer_pair {
+	struct iio_backend *back;
+	struct iio_buffer *buffer;
+};
+
+static LIST_HEAD(iio_back_list);
+static DEFINE_MUTEX(iio_back_lock);
+
+/*
+ * Helper macros to properly call backend ops. The main point for these macros
+ * is to properly lock the backend mutex on every call plus checking if the
+ * backend device is still around (by looking at the *ops pointer).
+ */
+
+#define iio_backend_check_op(back, op) ({ \
+	struct iio_backend *____back = back;				\
+	int ____ret = 0;						\
+									\
+	lockdep_assert_held(&____back->lock);				\
+	if (!____back->ops) {						\
+		pr_warn_once("Backend is no longer available\n");	\
+		____ret = -ENODEV;					\
+	} else if (!____back->ops->op) {				\
+		____ret = -EOPNOTSUPP;					\
+	}								\
+									\
+	____ret;								\
+})
+
+#define iio_backend_op_call(back, op, args...) ({		\
+	struct iio_backend *__back = back;			\
+	int __ret;						\
+								\
+	guard(mutex)(&__back->lock);				\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (!__ret)						\
+		__ret = __back->ops->op(__back, ##args);	\
+								\
+	__ret;							\
+})
+
+#define iio_backend_ptr_op_call(back, op, args...) ({		\
+	struct iio_backend *__back = back;			\
+	void *ptr_err;						\
+	int __ret;						\
+								\
+	guard(mutex)(&__back->lock);				\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (__ret)						\
+		ptr_err = ERR_PTR(__ret);			\
+	else							\
+		ptr_err = __back->ops->op(__back, ##args);	\
+								\
+	ptr_err;						\
+})
+
+#define iio_backend_void_op_call(back, op, args...) {		\
+	struct iio_backend *__back = back;			\
+	int __ret;						\
+								\
+	guard(mutex)(&__back->lock);				\
+	__ret = iio_backend_check_op(__back, op);		\
+	if (!__ret)						\
+		__back->ops->op(__back, ##args);		\
+}
+
+/**
+ * iio_backend_chan_enable - Enable a backend channel.
+ * @back:	Backend device.
+ * @chan:	Channel number.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan)
+{
+	return iio_backend_op_call(back, chan_enable, chan);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_chan_enable, IIO_BACKEND);
+
+/**
+ * iio_backend_chan_disable - Disable a backend channel.
+ * @back:	Backend device.
+ * @chan:	Channel number.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_chan_disable(struct iio_backend *back, unsigned int chan)
+{
+	return iio_backend_op_call(back, chan_disable, chan);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_chan_disable, IIO_BACKEND);
+
+/**
+ * iio_backend_chan_enable - Enable the backend.
+ * @back:	Backend device
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int iio_backend_enable(struct iio_backend *back)
+{
+	return iio_backend_op_call(back, enable);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_enable, IIO_BACKEND);
+
+/**
+ * iio_backend_disable - Disable the backend.
+ * @back:	Backend device
+ */
+void iio_backend_disable(struct iio_backend *back)
+{
+	iio_backend_void_op_call(back, disable);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_disable, IIO_BACKEND);
+
+/**
+ * iio_backend_data_format_set - Configure the channel data format
+ * @back:	Backend device
+ * @chan:	Channel number.
+ * @data:	Data format.
+ *
+ * Properly configure a channel with respect to the expected data format. A
+ * @struct iio_backend_data_fmt must be passed with the settings.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure
+ */
+int iio_backend_data_format_set(struct iio_backend *back, unsigned int chan,
+				const struct iio_backend_data_fmt *data)
+{
+	if (!data || data->type >= IIO_BACKEND_DATA_TYPE_MAX)
+		return -EINVAL;
+
+	return iio_backend_op_call(back, data_format_set, chan, data);
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_data_format_set, IIO_BACKEND);
+
+static void iio_backend_free_buffer(void *arg)
+{
+	struct iio_backend_buffer_pair *pair = arg;
+
+	iio_backend_void_op_call(pair->back, free_buffer, pair->buffer);
+}
+
+/**
+ * devm_iio_backend_request_buffer - Request an IIO buffer from the backend.
+ * @dev:	Device to bind the buffer lifetime.
+ * @back:	Backend device.
+ * @indio_dev:	IIO device.
+ *
+ * Request an IIO buffer from the backend. The type of the buffer (typically
+ * INDIO_BUFFER_HARDWARE) is up to the backend to decide. This is because,
+ * normally, the backend dictates what kind of buffering we can get.
+ *
+ * The backend .free_buffer() hooks is automatically called on @dev detach.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure
+ */
+int devm_iio_backend_request_buffer(struct device *dev,
+				    struct iio_backend *back,
+				    struct iio_dev *indio_dev)
+{
+	struct iio_backend_buffer_pair *pair;
+	struct iio_buffer *buffer;
+
+	buffer = iio_backend_ptr_op_call(back, request_buffer, indio_dev);
+	if (IS_ERR(buffer))
+		return PTR_ERR(buffer);
+
+	/* backend lock should not be need after getting the buffer */
+	pair = devm_kzalloc(dev, sizeof(*pair), GFP_KERNEL);
+	if (!pair)
+		return -ENOMEM;
+
+	/* weak reference should be all what we need */
+	pair->back = back;
+	pair->buffer = buffer;
+
+	return devm_add_action_or_reset(dev, iio_backend_free_buffer, pair);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_request_buffer, IIO_BACKEND);
+
+static void iio_backend_free(struct kref *ref)
+{
+	struct iio_backend *back = container_of(ref, struct iio_backend, ref);
+
+	kfree(back);
+}
+
+static void iio_backend_release(void *arg)
+{
+	struct iio_backend *back = arg;
+
+	module_put(back->owner);
+	kref_put(&back->ref, iio_backend_free);
+}
+
+static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
+{
+	struct device_link *link;
+	int ret;
+
+	kref_get(&back->ref);
+	if (!try_module_get(back->owner)) {
+		pr_err("%s: Cannot get module reference\n", dev_name(dev));
+		return -ENODEV;
+	}
+
+	ret = devm_add_action_or_reset(dev, iio_backend_release, back);
+	if (ret)
+		return ret;
+
+	link = device_link_add(dev, back->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
+	if (!link)
+		pr_warn("%s: Could not link to supplier(%s)\n", dev_name(dev),
+			dev_name(back->dev));
+
+	pr_debug("%s: Found backend(%s) device\n", dev_name(dev),
+		 dev_name(back->dev));
+	return 0;
+}
+
+/**
+ * devm_iio_backend_get - Get a backend device
+ * @dev:	Device where to look for the backend.
+ * @name:	Backend name.
+ *
+ * Get's the backend associated with @dev.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
+{
+	struct fwnode_handle *fwnode;
+	struct iio_backend *back;
+	int index = 0, ret;
+
+	if (name) {
+		index = device_property_match_string(dev, "io-backends-names",
+						     name);
+		if (index < 0)
+			return ERR_PTR(index);
+	}
+
+	fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
+	if (IS_ERR(fwnode)) {
+		/* not an error if optional */
+		pr_debug("%s: Cannot get Firmware reference\n", dev_name(dev));
+		return ERR_CAST(fwnode);
+	}
+
+	guard(mutex)(&iio_back_lock);
+	list_for_each_entry(back, &iio_back_list, entry) {
+		if (!device_match_fwnode(back->dev, fwnode))
+			continue;
+
+		fwnode_handle_put(fwnode);
+		ret = __devm_iio_backend_get(dev, back);
+		if (ret)
+			return ERR_PTR(ret);
+
+		return back;
+	}
+
+	fwnode_handle_put(fwnode);
+	return ERR_PTR(-EPROBE_DEFER);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, IIO_BACKEND);
+
+/**
+ * devm_iio_backend_get_optional - Get optional backend device
+ * @dev:	Device where to look for the backend.
+ * @name:	Backend name.
+ *
+ * Same as @devm_iio_backend_get() but return NULL if backend not found.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise or NULL if not found.
+ */
+struct iio_backend *devm_iio_backend_get_optional(struct device *dev,
+						  const char *name)
+{
+	struct iio_backend *back;
+
+	back = devm_iio_backend_get(dev, name);
+	if (IS_ERR(back) && PTR_ERR(back) == -ENOENT)
+		return NULL;
+
+	return back;
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_optional, IIO_BACKEND);
+
+/**
+ * devm_iio_backend_get_from_fwnode_lookup
+ * @dev:	Device where to bind the backend lifetime.
+ * @fwnode:	Firmware node of the backend device.
+ *
+ * It directly looks the backend device list for a device matching @fwnode.
+ * This API should not be used and it's only present for preventing the first
+ * user of this framework to break it's DT ABI.
+ *
+ * RETURNS:
+ * A backend pointer, negative error pointer otherwise.
+ */
+struct iio_backend *
+devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
+					struct fwnode_handle *fwnode)
+{
+	struct iio_backend *back;
+	int ret;
+
+	guard(mutex)(&iio_back_lock);
+	list_for_each_entry(back, &iio_back_list, entry) {
+		if (!device_match_fwnode(back->dev, fwnode))
+			continue;
+
+		ret = __devm_iio_backend_get(dev, back);
+		if (ret)
+			return ERR_PTR(ret);
+
+		return back;
+	}
+
+	return ERR_PTR(-EPROBE_DEFER);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_from_fwnode_lookup, IIO_BACKEND);
+
+/**
+ * iio_backend_get_priv - Get driver private data
+ * @back:	Backend device
+ */
+void *iio_backend_get_priv(const struct iio_backend *back)
+{
+	return back->priv;
+}
+EXPORT_SYMBOL_NS_GPL(iio_backend_get_priv, IIO_BACKEND);
+
+static void iio_backend_unregister(void *arg)
+{
+	struct iio_backend *back = arg;
+
+	mutex_lock(&iio_back_lock);
+	list_del(&back->entry);
+	mutex_unlock(&iio_back_lock);
+
+	mutex_lock(&back->lock);
+	back->ops = NULL;
+	mutex_unlock(&back->lock);
+	kref_put(&back->ref, iio_backend_free);
+}
+
+/**
+ * devm_iio_backend_register - Register a new backend device
+ * @dev:	Backend device being registered.
+ * @ops:	Backend ops
+ * @priv:	Device private data.
+ *
+ * @ops and @priv are both mandatory. Not providing them results in -EINVAL.
+ *
+ * RETURNS:
+ * 0 on success, negative error number on failure.
+ */
+int devm_iio_backend_register(struct device *dev,
+			      const struct iio_backend_ops *ops, void *priv)
+{
+	struct iio_backend *back;
+
+	if (!ops || !priv) {
+		pr_err("%s: No backend ops or private data given\n",
+		       dev_name(dev));
+		return -EINVAL;
+	}
+
+	back = kzalloc(sizeof(*back), GFP_KERNEL);
+	if (!back)
+		return -ENOMEM;
+
+	kref_init(&back->ref);
+	mutex_init(&back->lock);
+	back->ops = ops;
+	back->owner = dev->driver->owner;
+	back->dev = dev;
+	back->priv = priv;
+	mutex_lock(&iio_back_lock);
+	list_add(&back->entry, &iio_back_list);
+	mutex_unlock(&iio_back_lock);
+
+	return devm_add_action_or_reset(dev, iio_backend_unregister, back);
+}
+EXPORT_SYMBOL_NS_GPL(devm_iio_backend_register, IIO_BACKEND);
+
+MODULE_AUTHOR("Nuno Sa <nuno.sa@analog.com>");
+MODULE_DESCRIPTION("Framework to handle complex IIO aggregate devices");
+MODULE_LICENSE("GPL");
diff --git a/include/linux/iio/backend.h b/include/linux/iio/backend.h
new file mode 100644
index 000000000000..239d4db08cee
--- /dev/null
+++ b/include/linux/iio/backend.h
@@ -0,0 +1,75 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later */
+#ifndef _IIO_BACKEND_H_
+#define _IIO_BACKEND_H_
+
+#include <linux/types.h>
+
+struct fwnode_handle;
+struct iio_backend;
+struct device;
+struct iio_dev;
+
+enum iio_backend_data_type {
+	IIO_BACKEND_TWOS_COMPLEMENT,
+	IIO_BACKEND_OFFSET_BINARY,
+	IIO_BACKEND_DATA_TYPE_MAX
+};
+
+/**
+ * struct iio_backend_data_fmt - Backend data format
+ * @type:		Data type.
+ * @sign_extend:	Bool to tell if the data is sign extended.
+ * @enable:		Enable/Disable the data format module. If disabled,
+ *			not formatting will happen.
+ */
+struct iio_backend_data_fmt {
+	enum iio_backend_data_type type;
+	bool sign_extend;
+	bool enable;
+};
+
+/**
+ * struct iio_backend_ops - operations structure for an iio_backend
+ * @enable:		Enable backend.
+ * @disable:		Disable backend.
+ * @chan_enable:	Enable one channel.
+ * @chan_disable:	Disable one channel.
+ * @data_format_set:	Configure the data format for a specific channel.
+ * @request_buffer:	Request an IIO buffer.
+ * @free_buffer:	Free an IIO buffer.
+ **/
+struct iio_backend_ops {
+	int (*enable)(struct iio_backend *back);
+	void (*disable)(struct iio_backend *back);
+	int (*chan_enable)(struct iio_backend *back, unsigned int chan);
+	int (*chan_disable)(struct iio_backend *back, unsigned int chan);
+	int (*data_format_set)(struct iio_backend *back, unsigned int chan,
+			       const struct iio_backend_data_fmt *data);
+	struct iio_buffer *(*request_buffer)(struct iio_backend *back,
+					     struct iio_dev *indio_dev);
+	void (*free_buffer)(struct iio_backend *back,
+			    struct iio_buffer *buffer);
+};
+
+int iio_backend_chan_enable(struct iio_backend *back, unsigned int chan);
+int iio_backend_chan_disable(struct iio_backend *back, unsigned int chan);
+int iio_backend_enable(struct iio_backend *back);
+void iio_backend_disable(struct iio_backend *back);
+int iio_backend_data_format_set(struct iio_backend *back, unsigned int chan,
+				const struct iio_backend_data_fmt *data);
+int devm_iio_backend_request_buffer(struct device *dev,
+				    struct iio_backend *back,
+				    struct iio_dev *indio_dev);
+
+void *iio_backend_get_priv(const struct iio_backend *conv);
+struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name);
+struct iio_backend *devm_iio_backend_get_optional(struct device *dev,
+						  const char *name);
+struct iio_backend *
+devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
+					struct fwnode_handle *fwnode);
+
+int devm_iio_backend_register(struct device *dev,
+			      const struct iio_backend_ops *ops, void *priv);
+
+#endif

-- 
2.43.0

[PATCH v4 7/8] iio: adc: ad9467: convert to backend framework

[Nuno Sa]

Convert the driver to use the new IIO backend framework. The device
functionality is expected to be the same (meaning no added or removed
features).

Also note this patch effectively breaks ABI and that's needed so we can
properly support this device and add needed features making use of the
new IIO framework.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/Kconfig  |   2 +-
 drivers/iio/adc/ad9467.c | 282 ++++++++++++++++++++++++++++++-----------------
 2 files changed, 182 insertions(+), 102 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 4eebd5161419..10e0e340cdae 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -275,7 +275,7 @@ config AD799X
 config AD9467
 	tristate "Analog Devices AD9467 High Speed ADC driver"
 	depends on SPI
-	depends on ADI_AXI_ADC
+	select IIO_BACKEND
 	help
 	  Say yes here to build support for Analog Devices:
 	  * AD9467 16-Bit, 200 MSPS/250 MSPS Analog-to-Digital Converter
diff --git a/drivers/iio/adc/ad9467.c b/drivers/iio/adc/ad9467.c
index 6581fce4ba95..c9f48ac19cd2 100644
--- a/drivers/iio/adc/ad9467.c
+++ b/drivers/iio/adc/ad9467.c
@@ -17,13 +17,12 @@
 #include <linux/of.h>
 
 
+#include <linux/iio/backend.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/sysfs.h>
 
 #include <linux/clk.h>
 
-#include <linux/iio/adc/adi-axi-adc.h>
-
 /*
  * ADI High-Speed ADC common spi interface registers
  * See Application-Note AN-877:
@@ -102,15 +101,20 @@
 #define AD9467_REG_VREF_MASK		0x0F
 
 struct ad9467_chip_info {
-	struct adi_axi_adc_chip_info	axi_adc_info;
-	unsigned int			default_output_mode;
-	unsigned int			vref_mask;
+	const char		*name;
+	unsigned int		id;
+	const struct		iio_chan_spec *channels;
+	unsigned int		num_channels;
+	const unsigned int	(*scale_table)[2];
+	int			num_scales;
+	unsigned long		max_rate;
+	unsigned int		default_output_mode;
+	unsigned int		vref_mask;
 };
 
-#define to_ad9467_chip_info(_info)	\
-	container_of(_info, struct ad9467_chip_info, axi_adc_info)
-
 struct ad9467_state {
+	const struct ad9467_chip_info	*info;
+	struct iio_backend		*back;
 	struct spi_device		*spi;
 	struct clk			*clk;
 	unsigned int			output_mode;
@@ -151,10 +155,10 @@ static int ad9467_spi_write(struct spi_device *spi, unsigned int reg,
 	return spi_write(spi, buf, ARRAY_SIZE(buf));
 }
 
-static int ad9467_reg_access(struct adi_axi_adc_conv *conv, unsigned int reg,
+static int ad9467_reg_access(struct iio_dev *indio_dev, unsigned int reg,
 			     unsigned int writeval, unsigned int *readval)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 	struct spi_device *spi = st->spi;
 	int ret;
 
@@ -191,14 +195,13 @@ static const unsigned int ad9467_scale_table[][2] = {
 	{2300, 8}, {2400, 9}, {2500, 10},
 };
 
-static void __ad9467_get_scale(struct adi_axi_adc_conv *conv, int index,
+static void __ad9467_get_scale(struct ad9467_state *st, int index,
 			       unsigned int *val, unsigned int *val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	const struct iio_chan_spec *chan = &info->channels[0];
+	const struct iio_chan_spec *chan = &st->info->channels[0];
 	unsigned int tmp;
 
-	tmp = (info->scale_table[index][0] * 1000000ULL) >>
+	tmp = (st->info->scale_table[index][0] * 1000000ULL) >>
 			chan->scan_type.realbits;
 	*val = tmp / 1000000;
 	*val2 = tmp % 1000000;
@@ -229,52 +232,43 @@ static const struct iio_chan_spec ad9467_channels[] = {
 };
 
 static const struct ad9467_chip_info ad9467_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9467",
-		.id = CHIPID_AD9467,
-		.max_rate = 250000000UL,
-		.scale_table = ad9467_scale_table,
-		.num_scales = ARRAY_SIZE(ad9467_scale_table),
-		.channels = ad9467_channels,
-		.num_channels = ARRAY_SIZE(ad9467_channels),
-	},
+	.name = "ad9467",
+	.id = CHIPID_AD9467,
+	.max_rate = 250000000UL,
+	.scale_table = ad9467_scale_table,
+	.num_scales = ARRAY_SIZE(ad9467_scale_table),
+	.channels = ad9467_channels,
+	.num_channels = ARRAY_SIZE(ad9467_channels),
 	.default_output_mode = AD9467_DEF_OUTPUT_MODE,
 	.vref_mask = AD9467_REG_VREF_MASK,
 };
 
 static const struct ad9467_chip_info ad9434_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9434",
-		.id = CHIPID_AD9434,
-		.max_rate = 500000000UL,
-		.scale_table = ad9434_scale_table,
-		.num_scales = ARRAY_SIZE(ad9434_scale_table),
-		.channels = ad9434_channels,
-		.num_channels = ARRAY_SIZE(ad9434_channels),
-	},
+	.name = "ad9434",
+	.id = CHIPID_AD9434,
+	.max_rate = 500000000UL,
+	.scale_table = ad9434_scale_table,
+	.num_scales = ARRAY_SIZE(ad9434_scale_table),
+	.channels = ad9434_channels,
+	.num_channels = ARRAY_SIZE(ad9434_channels),
 	.default_output_mode = AD9434_DEF_OUTPUT_MODE,
 	.vref_mask = AD9434_REG_VREF_MASK,
 };
 
 static const struct ad9467_chip_info ad9265_chip_tbl = {
-	.axi_adc_info = {
-		.name = "ad9265",
-		.id = CHIPID_AD9265,
-		.max_rate = 125000000UL,
-		.scale_table = ad9265_scale_table,
-		.num_scales = ARRAY_SIZE(ad9265_scale_table),
-		.channels = ad9467_channels,
-		.num_channels = ARRAY_SIZE(ad9467_channels),
-	},
+	.name = "ad9265",
+	.id = CHIPID_AD9265,
+	.max_rate = 125000000UL,
+	.scale_table = ad9265_scale_table,
+	.num_scales = ARRAY_SIZE(ad9265_scale_table),
+	.channels = ad9467_channels,
+	.num_channels = ARRAY_SIZE(ad9467_channels),
 	.default_output_mode = AD9265_DEF_OUTPUT_MODE,
 	.vref_mask = AD9265_REG_VREF_MASK,
 };
 
-static int ad9467_get_scale(struct adi_axi_adc_conv *conv, int *val, int *val2)
+static int ad9467_get_scale(struct ad9467_state *st, int *val, int *val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	const struct ad9467_chip_info *info1 = to_ad9467_chip_info(info);
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
 	unsigned int i, vref_val;
 	int ret;
 
@@ -282,25 +276,23 @@ static int ad9467_get_scale(struct adi_axi_adc_conv *conv, int *val, int *val2)
 	if (ret < 0)
 		return ret;
 
-	vref_val = ret & info1->vref_mask;
+	vref_val = ret & st->info->vref_mask;
 
-	for (i = 0; i < info->num_scales; i++) {
-		if (vref_val == info->scale_table[i][1])
+	for (i = 0; i < st->info->num_scales; i++) {
+		if (vref_val == st->info->scale_table[i][1])
 			break;
 	}
 
-	if (i == info->num_scales)
+	if (i == st->info->num_scales)
 		return -ERANGE;
 
-	__ad9467_get_scale(conv, i, val, val2);
+	__ad9467_get_scale(st, i, val, val2);
 
 	return IIO_VAL_INT_PLUS_MICRO;
 }
 
-static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
+static int ad9467_set_scale(struct ad9467_state *st, int val, int val2)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
 	unsigned int scale_val[2];
 	unsigned int i;
 	int ret;
@@ -308,14 +300,14 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
 	if (val != 0)
 		return -EINVAL;
 
-	for (i = 0; i < info->num_scales; i++) {
-		__ad9467_get_scale(conv, i, &scale_val[0], &scale_val[1]);
+	for (i = 0; i < st->info->num_scales; i++) {
+		__ad9467_get_scale(st, i, &scale_val[0], &scale_val[1]);
 		if (scale_val[0] != val || scale_val[1] != val2)
 			continue;
 
 		guard(mutex)(&st->lock);
 		ret = ad9467_spi_write(st->spi, AN877_ADC_REG_VREF,
-				       info->scale_table[i][1]);
+				       st->info->scale_table[i][1]);
 		if (ret < 0)
 			return ret;
 
@@ -326,15 +318,15 @@ static int ad9467_set_scale(struct adi_axi_adc_conv *conv, int val, int val2)
 	return -EINVAL;
 }
 
-static int ad9467_read_raw(struct adi_axi_adc_conv *conv,
+static int ad9467_read_raw(struct iio_dev *indio_dev,
 			   struct iio_chan_spec const *chan,
 			   int *val, int *val2, long m)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 
 	switch (m) {
 	case IIO_CHAN_INFO_SCALE:
-		return ad9467_get_scale(conv, val, val2);
+		return ad9467_get_scale(st, val, val2);
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		*val = clk_get_rate(st->clk);
 
@@ -344,20 +336,19 @@ static int ad9467_read_raw(struct adi_axi_adc_conv *conv,
 	}
 }
 
-static int ad9467_write_raw(struct adi_axi_adc_conv *conv,
+static int ad9467_write_raw(struct iio_dev *indio_dev,
 			    struct iio_chan_spec const *chan,
 			    int val, int val2, long mask)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 	long r_clk;
 
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
-		return ad9467_set_scale(conv, val, val2);
+		return ad9467_set_scale(st, val, val2);
 	case IIO_CHAN_INFO_SAMP_FREQ:
 		r_clk = clk_round_rate(st->clk, val);
-		if (r_clk < 0 || r_clk > info->max_rate) {
+		if (r_clk < 0 || r_clk > st->info->max_rate) {
 			dev_warn(&st->spi->dev,
 				 "Error setting ADC sample rate %ld", r_clk);
 			return -EINVAL;
@@ -369,26 +360,53 @@ static int ad9467_write_raw(struct adi_axi_adc_conv *conv,
 	}
 }
 
-static int ad9467_read_avail(struct adi_axi_adc_conv *conv,
+static int ad9467_read_avail(struct iio_dev *indio_dev,
 			     struct iio_chan_spec const *chan,
 			     const int **vals, int *type, int *length,
 			     long mask)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct ad9467_state *st = iio_priv(indio_dev);
 
 	switch (mask) {
 	case IIO_CHAN_INFO_SCALE:
 		*vals = (const int *)st->scales;
 		*type = IIO_VAL_INT_PLUS_MICRO;
 		/* Values are stored in a 2D matrix */
-		*length = info->num_scales * 2;
+		*length = st->info->num_scales * 2;
 		return IIO_AVAIL_LIST;
 	default:
 		return -EINVAL;
 	}
 }
 
+static int ad9467_update_scan_mode(struct iio_dev *indio_dev,
+				   const unsigned long *scan_mask)
+{
+	struct ad9467_state *st = iio_priv(indio_dev);
+	unsigned int c;
+	int ret;
+
+	for (c = 0; c < st->info->num_channels; c++) {
+		if (test_bit(c, scan_mask))
+			ret = iio_backend_chan_enable(st->back, c);
+		else
+			ret = iio_backend_chan_disable(st->back, c);
+
+		if (ret)
+			return ret;
+	}
+
+	return 0;
+}
+
+static const struct iio_info ad9467_info = {
+	.read_raw = ad9467_read_raw,
+	.write_raw = ad9467_write_raw,
+	.update_scan_mode = ad9467_update_scan_mode,
+	.debugfs_reg_access = ad9467_reg_access,
+	.read_avail = ad9467_read_avail,
+};
+
 static int ad9467_outputmode_set(struct spi_device *spi, unsigned int mode)
 {
 	int ret;
@@ -401,19 +419,17 @@ static int ad9467_outputmode_set(struct spi_device *spi, unsigned int mode)
 				AN877_ADC_TRANSFER_SYNC);
 }
 
-static int ad9467_scale_fill(struct adi_axi_adc_conv *conv)
+static int ad9467_scale_fill(struct ad9467_state *st)
 {
-	const struct adi_axi_adc_chip_info *info = conv->chip_info;
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
 	unsigned int i, val1, val2;
 
-	st->scales = devm_kmalloc_array(&st->spi->dev, info->num_scales,
+	st->scales = devm_kmalloc_array(&st->spi->dev, st->info->num_scales,
 					sizeof(*st->scales), GFP_KERNEL);
 	if (!st->scales)
 		return -ENOMEM;
 
-	for (i = 0; i < info->num_scales; i++) {
-		__ad9467_get_scale(conv, i, &val1, &val2);
+	for (i = 0; i < st->info->num_scales; i++) {
+		__ad9467_get_scale(st, i, &val1, &val2);
 		st->scales[i][0] = val1;
 		st->scales[i][1] = val2;
 	}
@@ -421,11 +437,27 @@ static int ad9467_scale_fill(struct adi_axi_adc_conv *conv)
 	return 0;
 }
 
-static int ad9467_preenable_setup(struct adi_axi_adc_conv *conv)
+static int ad9467_setup(struct ad9467_state *st)
 {
-	struct ad9467_state *st = adi_axi_adc_conv_priv(conv);
+	struct iio_backend_data_fmt data = {
+		.sign_extend = true,
+		.enable = true,
+	};
+	unsigned int c, mode;
+	int ret;
+
+	mode = st->info->default_output_mode | AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
+	ret = ad9467_outputmode_set(st->spi, mode);
+	if (ret)
+		return ret;
 
-	return ad9467_outputmode_set(st->spi, st->output_mode);
+	for (c = 0; c < st->info->num_channels; c++) {
+		ret = iio_backend_data_format_set(st->back, c, &data);
+		if (ret)
+			return ret;
+	}
+
+	return 0;
 }
 
 static int ad9467_reset(struct device *dev)
@@ -443,25 +475,63 @@ static int ad9467_reset(struct device *dev)
 	return 0;
 }
 
+static int ad9467_iio_backend_get(struct ad9467_state *st)
+{
+	struct device *dev = &st->spi->dev;
+	struct device_node *__back;
+
+	st->back = devm_iio_backend_get_optional(&st->spi->dev, NULL);
+	if (IS_ERR(st->back))
+		return PTR_ERR(st->back);
+	if (st->back)
+		return 0;
+	/*
+	 * if we don't get the backend using the normal API's, use the legacy
+	 * 'adi,adc-dev' property. So we get all nodes with that property, and
+	 * look for the one pointing at us. Then we directly lookup that fwnode
+	 * on the backend list of registered devices. This is done so we don't
+	 * make io-backends mandatory which would break DT ABI.
+	 */
+	for_each_node_with_property(__back, "adi,adc-dev") {
+		struct device_node *__me;
+
+		__me = of_parse_phandle(__back, "adi,adc-dev", 0);
+		if (!__me)
+			continue;
+
+		if (!device_match_of_node(dev, __me)) {
+			of_node_put(__me);
+			continue;
+		}
+
+		of_node_put(__me);
+		st->back = devm_iio_backend_get_from_fwnode_lookup(dev,
+								   of_fwnode_handle(__back));
+		of_node_put(__back);
+		return PTR_ERR_OR_ZERO(st->back);
+	}
+
+	return -ENODEV;
+}
+
 static int ad9467_probe(struct spi_device *spi)
 {
-	const struct ad9467_chip_info *info;
-	struct adi_axi_adc_conv *conv;
+	struct iio_dev *indio_dev;
 	struct ad9467_state *st;
 	unsigned int id;
 	int ret;
 
-	info = spi_get_device_match_data(spi);
-	if (!info)
-		return -ENODEV;
-
-	conv = devm_adi_axi_adc_conv_register(&spi->dev, sizeof(*st));
-	if (IS_ERR(conv))
-		return PTR_ERR(conv);
+	indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
+	if (!indio_dev)
+		return -ENOMEM;
 
-	st = adi_axi_adc_conv_priv(conv);
+	st = iio_priv(indio_dev);
 	st->spi = spi;
 
+	st->info = spi_get_device_match_data(spi);
+	if (!st->info)
+		return -ENODEV;
+
 	st->clk = devm_clk_get_enabled(&spi->dev, "adc-clk");
 	if (IS_ERR(st->clk))
 		return PTR_ERR(st->clk);
@@ -475,29 +545,39 @@ static int ad9467_probe(struct spi_device *spi)
 	if (ret)
 		return ret;
 
-	conv->chip_info = &info->axi_adc_info;
-
-	ret = ad9467_scale_fill(conv);
+	ret = ad9467_scale_fill(st);
 	if (ret)
 		return ret;
 
 	id = ad9467_spi_read(spi, AN877_ADC_REG_CHIP_ID);
-	if (id != conv->chip_info->id) {
+	if (id != st->info->id) {
 		dev_err(&spi->dev, "Mismatch CHIP_ID, got 0x%X, expected 0x%X\n",
-			id, conv->chip_info->id);
+			id, st->info->id);
 		return -ENODEV;
 	}
 
-	conv->reg_access = ad9467_reg_access;
-	conv->write_raw = ad9467_write_raw;
-	conv->read_raw = ad9467_read_raw;
-	conv->read_avail = ad9467_read_avail;
-	conv->preenable_setup = ad9467_preenable_setup;
+	indio_dev->name = st->info->name;
+	indio_dev->channels = st->info->channels;
+	indio_dev->num_channels = st->info->num_channels;
+	indio_dev->info = &ad9467_info;
 
-	st->output_mode = info->default_output_mode |
-			  AN877_ADC_OUTPUT_MODE_TWOS_COMPLEMENT;
+	ret = ad9467_iio_backend_get(st);
+	if (ret)
+		return ret;
 
-	return 0;
+	ret = devm_iio_backend_request_buffer(&spi->dev, st->back, indio_dev);
+	if (ret)
+		return ret;
+
+	ret = iio_backend_enable(st->back);
+	if (ret)
+		return ret;
+
+	ret = ad9467_setup(st);
+	if (ret)
+		return ret;
+
+	return devm_iio_device_register(&spi->dev, indio_dev);
 }
 
 static const struct of_device_id ad9467_of_match[] = {
@@ -529,4 +609,4 @@ module_spi_driver(ad9467_driver);
 MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices AD9467 ADC driver");
 MODULE_LICENSE("GPL v2");
-MODULE_IMPORT_NS(IIO_ADI_AXI);
+MODULE_IMPORT_NS(IIO_BACKEND);

-- 
2.43.0

[PATCH v4 8/8] iio: adc: adi-axi-adc: move to backend framework

[Nuno Sa]

Move to the IIO backend framework. Devices supported by adi-axi-adc now
register themselves as backend devices.

Signed-off-by: Nuno Sa <nuno.sa@analog.com>
---
 drivers/iio/adc/Kconfig             |   2 +-
 drivers/iio/adc/adi-axi-adc.c       | 380 +++++++++---------------------------
 include/linux/iio/adc/adi-axi-adc.h |  68 -------
 3 files changed, 93 insertions(+), 357 deletions(-)

diff --git a/drivers/iio/adc/Kconfig b/drivers/iio/adc/Kconfig
index 10e0e340cdae..b64e0d442a19 100644
--- a/drivers/iio/adc/Kconfig
+++ b/drivers/iio/adc/Kconfig
@@ -293,7 +293,7 @@ config ADI_AXI_ADC
 	select IIO_BUFFER_HW_CONSUMER
 	select IIO_BUFFER_DMAENGINE
 	select REGMAP_MMIO
-	depends on OF
+	select IIO_BACKEND
 	help
 	  Say yes here to build support for Analog Devices Generic
 	  AXI ADC IP core. The IP core is used for interfacing with
diff --git a/drivers/iio/adc/adi-axi-adc.c b/drivers/iio/adc/adi-axi-adc.c
index 0f21d1d98b9f..741b53c25bb1 100644
--- a/drivers/iio/adc/adi-axi-adc.c
+++ b/drivers/iio/adc/adi-axi-adc.c
@@ -8,6 +8,7 @@
 
 #include <linux/bitfield.h>
 #include <linux/clk.h>
+#include <linux/err.h>
 #include <linux/io.h>
 #include <linux/delay.h>
 #include <linux/module.h>
@@ -17,13 +18,11 @@
 #include <linux/regmap.h>
 #include <linux/slab.h>
 
-#include <linux/iio/iio.h>
-#include <linux/iio/sysfs.h>
-#include <linux/iio/buffer.h>
-#include <linux/iio/buffer-dmaengine.h>
-
 #include <linux/fpga/adi-axi-common.h>
-#include <linux/iio/adc/adi-axi-adc.h>
+#include <linux/iio/backend.h>
+#include <linux/iio/buffer-dmaengine.h>
+#include <linux/iio/buffer.h>
+#include <linux/iio/iio.h>
 
 /*
  * Register definitions:
@@ -44,6 +43,7 @@
 #define   ADI_AXI_REG_CHAN_CTRL_PN_SEL_OWR	BIT(10)
 #define   ADI_AXI_REG_CHAN_CTRL_IQCOR_EN	BIT(9)
 #define   ADI_AXI_REG_CHAN_CTRL_DCFILT_EN	BIT(8)
+#define   ADI_AXI_REG_CHAN_CTRL_FMT_MASK	GENMASK(6, 4)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_SIGNEXT	BIT(6)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_TYPE	BIT(5)
 #define   ADI_AXI_REG_CHAN_CTRL_FMT_EN		BIT(4)
@@ -55,286 +55,100 @@
 	 ADI_AXI_REG_CHAN_CTRL_FMT_EN |		\
 	 ADI_AXI_REG_CHAN_CTRL_ENABLE)
 
-struct adi_axi_adc_core_info {
-	unsigned int				version;
-};
-
 struct adi_axi_adc_state {
-	struct mutex				lock;
-
-	struct adi_axi_adc_client		*client;
 	struct regmap				*regmap;
-};
-
-struct adi_axi_adc_client {
-	struct list_head			entry;
-	struct adi_axi_adc_conv			conv;
-	struct adi_axi_adc_state		*state;
 	struct device				*dev;
-	const struct adi_axi_adc_core_info	*info;
 };
 
-static LIST_HEAD(registered_clients);
-static DEFINE_MUTEX(registered_clients_lock);
-
-static struct adi_axi_adc_client *conv_to_client(struct adi_axi_adc_conv *conv)
-{
-	return container_of(conv, struct adi_axi_adc_client, conv);
-}
-
-void *adi_axi_adc_conv_priv(struct adi_axi_adc_conv *conv)
-{
-	struct adi_axi_adc_client *cl = conv_to_client(conv);
-
-	return (char *)cl + ALIGN(sizeof(struct adi_axi_adc_client),
-				  IIO_DMA_MINALIGN);
-}
-EXPORT_SYMBOL_NS_GPL(adi_axi_adc_conv_priv, IIO_ADI_AXI);
-
-static int adi_axi_adc_config_dma_buffer(struct device *dev,
-					 struct iio_dev *indio_dev)
-{
-	const char *dma_name;
-
-	if (!device_property_present(dev, "dmas"))
-		return 0;
-
-	if (device_property_read_string(dev, "dma-names", &dma_name))
-		dma_name = "rx";
-
-	return devm_iio_dmaengine_buffer_setup(indio_dev->dev.parent,
-					       indio_dev, dma_name);
-}
-
-static int adi_axi_adc_read_raw(struct iio_dev *indio_dev,
-				struct iio_chan_spec const *chan,
-				int *val, int *val2, long mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->read_raw)
-		return -EOPNOTSUPP;
-
-	return conv->read_raw(conv, chan, val, val2, mask);
-}
-
-static int adi_axi_adc_write_raw(struct iio_dev *indio_dev,
-				 struct iio_chan_spec const *chan,
-				 int val, int val2, long mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->write_raw)
-		return -EOPNOTSUPP;
-
-	return conv->write_raw(conv, chan, val, val2, mask);
-}
-
-static int adi_axi_adc_read_avail(struct iio_dev *indio_dev,
-				  struct iio_chan_spec const *chan,
-				  const int **vals, int *type, int *length,
-				  long mask)
+static int axi_adc_enable(struct iio_backend *back)
 {
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-
-	if (!conv->read_avail)
-		return -EOPNOTSUPP;
-
-	return conv->read_avail(conv, chan, vals, type, length, mask);
-}
-
-static int adi_axi_adc_update_scan_mode(struct iio_dev *indio_dev,
-					const unsigned long *scan_mask)
-{
-	struct adi_axi_adc_state *st = iio_priv(indio_dev);
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-	unsigned int i;
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 	int ret;
 
-	for (i = 0; i < conv->chip_info->num_channels; i++) {
-		if (test_bit(i, scan_mask))
-			ret = regmap_set_bits(st->regmap,
-					      ADI_AXI_REG_CHAN_CTRL(i),
-					      ADI_AXI_REG_CHAN_CTRL_ENABLE);
-		else
-			ret = regmap_clear_bits(st->regmap,
-						ADI_AXI_REG_CHAN_CTRL(i),
-						ADI_AXI_REG_CHAN_CTRL_ENABLE);
-		if (ret)
-			return ret;
-	}
+	ret = regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
+			      ADI_AXI_REG_RSTN_MMCM_RSTN);
+	if (ret)
+		return ret;
 
-	return 0;
+	fsleep(10);
+	return regmap_set_bits(st->regmap, ADI_AXI_REG_RSTN,
+			       ADI_AXI_REG_RSTN_RSTN | ADI_AXI_REG_RSTN_MMCM_RSTN);
 }
 
-static struct adi_axi_adc_conv *adi_axi_adc_conv_register(struct device *dev,
-							  size_t sizeof_priv)
+static void axi_adc_disable(struct iio_backend *back)
 {
-	struct adi_axi_adc_client *cl;
-	size_t alloc_size;
-
-	alloc_size = ALIGN(sizeof(struct adi_axi_adc_client), IIO_DMA_MINALIGN);
-	if (sizeof_priv)
-		alloc_size += ALIGN(sizeof_priv, IIO_DMA_MINALIGN);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	cl = kzalloc(alloc_size, GFP_KERNEL);
-	if (!cl)
-		return ERR_PTR(-ENOMEM);
-
-	mutex_lock(&registered_clients_lock);
-
-	cl->dev = get_device(dev);
-
-	list_add_tail(&cl->entry, &registered_clients);
-
-	mutex_unlock(&registered_clients_lock);
-
-	return &cl->conv;
+	regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
 }
 
-static void adi_axi_adc_conv_unregister(struct adi_axi_adc_conv *conv)
+static int axi_adc_data_format_set(struct iio_backend *back, unsigned int chan,
+				   const struct iio_backend_data_fmt *data)
 {
-	struct adi_axi_adc_client *cl = conv_to_client(conv);
-
-	mutex_lock(&registered_clients_lock);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
+	u32 val;
 
-	list_del(&cl->entry);
-	put_device(cl->dev);
+	if (!data->enable)
+		return regmap_clear_bits(st->regmap,
+					 ADI_AXI_REG_CHAN_CTRL(chan),
+					 ADI_AXI_REG_CHAN_CTRL_FMT_EN);
 
-	mutex_unlock(&registered_clients_lock);
+	val = FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_EN, true);
+	if (data->sign_extend)
+		val |= FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_SIGNEXT, true);
+	if (data->type == IIO_BACKEND_OFFSET_BINARY)
+		val |= FIELD_PREP(ADI_AXI_REG_CHAN_CTRL_FMT_TYPE, true);
 
-	kfree(cl);
+	return regmap_update_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+				  ADI_AXI_REG_CHAN_CTRL_FMT_MASK, val);
 }
 
-static void devm_adi_axi_adc_conv_release(void *conv)
+static int axi_adc_chan_enable(struct iio_backend *back, unsigned int chan)
 {
-	adi_axi_adc_conv_unregister(conv);
-}
-
-struct adi_axi_adc_conv *devm_adi_axi_adc_conv_register(struct device *dev,
-							size_t sizeof_priv)
-{
-	struct adi_axi_adc_conv *conv;
-	int ret;
-
-	conv = adi_axi_adc_conv_register(dev, sizeof_priv);
-	if (IS_ERR(conv))
-		return conv;
-
-	ret = devm_add_action_or_reset(dev, devm_adi_axi_adc_conv_release,
-				       conv);
-	if (ret)
-		return ERR_PTR(ret);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	return conv;
+	return regmap_set_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+			       ADI_AXI_REG_CHAN_CTRL_ENABLE);
 }
-EXPORT_SYMBOL_NS_GPL(devm_adi_axi_adc_conv_register, IIO_ADI_AXI);
-
-static const struct iio_info adi_axi_adc_info = {
-	.read_raw = &adi_axi_adc_read_raw,
-	.write_raw = &adi_axi_adc_write_raw,
-	.update_scan_mode = &adi_axi_adc_update_scan_mode,
-	.read_avail = &adi_axi_adc_read_avail,
-};
 
-static const struct adi_axi_adc_core_info adi_axi_adc_10_0_a_info = {
-	.version = ADI_AXI_PCORE_VER(10, 0, 'a'),
-};
-
-static struct adi_axi_adc_client *adi_axi_adc_attach_client(struct device *dev)
+static int axi_adc_chan_disable(struct iio_backend *back, unsigned int chan)
 {
-	const struct adi_axi_adc_core_info *info;
-	struct adi_axi_adc_client *cl;
-	struct device_node *cln;
-
-	info = of_device_get_match_data(dev);
-	if (!info)
-		return ERR_PTR(-ENODEV);
-
-	cln = of_parse_phandle(dev->of_node, "adi,adc-dev", 0);
-	if (!cln) {
-		dev_err(dev, "No 'adi,adc-dev' node defined\n");
-		return ERR_PTR(-ENODEV);
-	}
-
-	mutex_lock(&registered_clients_lock);
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
 
-	list_for_each_entry(cl, &registered_clients, entry) {
-		if (!cl->dev)
-			continue;
-
-		if (cl->dev->of_node != cln)
-			continue;
-
-		if (!try_module_get(cl->dev->driver->owner)) {
-			mutex_unlock(&registered_clients_lock);
-			of_node_put(cln);
-			return ERR_PTR(-ENODEV);
-		}
-
-		get_device(cl->dev);
-		cl->info = info;
-		mutex_unlock(&registered_clients_lock);
-		of_node_put(cln);
-		return cl;
-	}
-
-	mutex_unlock(&registered_clients_lock);
-	of_node_put(cln);
-
-	return ERR_PTR(-EPROBE_DEFER);
+	return regmap_clear_bits(st->regmap, ADI_AXI_REG_CHAN_CTRL(chan),
+				 ADI_AXI_REG_CHAN_CTRL_ENABLE);
 }
 
-static int adi_axi_adc_setup_channels(struct device *dev,
-				      struct adi_axi_adc_state *st)
+static struct iio_buffer *axi_adc_request_buffer(struct iio_backend *back,
+						 struct iio_dev *indio_dev)
 {
-	struct adi_axi_adc_conv *conv = &st->client->conv;
-	int i, ret;
+	struct adi_axi_adc_state *st = iio_backend_get_priv(back);
+	struct iio_buffer *buffer;
+	const char *dma_name;
+	int ret;
 
-	if (conv->preenable_setup) {
-		ret = conv->preenable_setup(conv);
-		if (ret)
-			return ret;
-	}
+	if (device_property_read_string(st->dev, "dma-names", &dma_name))
+		dma_name = "rx";
 
-	for (i = 0; i < conv->chip_info->num_channels; i++) {
-		ret = regmap_write(st->regmap, ADI_AXI_REG_CHAN_CTRL(i),
-				   ADI_AXI_REG_CHAN_CTRL_DEFAULTS);
-		if (ret)
-			return ret;
+	buffer = iio_dmaengine_buffer_alloc(st->dev, dma_name);
+	if (IS_ERR(buffer)) {
+		dev_err(st->dev, "Could not get DMA buffer, %ld\n",
+			PTR_ERR(buffer));
+		return ERR_CAST(buffer);
 	}
 
-	return 0;
-}
-
-static int axi_adc_reset(struct adi_axi_adc_state *st)
-{
-	int ret;
-
-	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
-	if (ret)
-		return ret;
-
-	mdelay(10);
-	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN,
-			   ADI_AXI_REG_RSTN_MMCM_RSTN);
+	indio_dev->modes |= INDIO_BUFFER_HARDWARE;
+	ret = iio_device_attach_buffer(indio_dev, buffer);
 	if (ret)
-		return ret;
+		return ERR_PTR(ret);
 
-	mdelay(10);
-	return regmap_write(st->regmap, ADI_AXI_REG_RSTN,
-			    ADI_AXI_REG_RSTN_RSTN | ADI_AXI_REG_RSTN_MMCM_RSTN);
+	return buffer;
 }
 
-static void adi_axi_adc_cleanup(void *data)
+static void axi_adc_free_buffer(struct iio_backend *back,
+				struct iio_buffer *buffer)
 {
-	struct adi_axi_adc_client *cl = data;
-
-	put_device(cl->dev);
-	module_put(cl->dev->driver->owner);
+	iio_dmaengine_buffer_free(buffer);
 }
 
 static const struct regmap_config axi_adc_regmap_config = {
@@ -344,45 +158,46 @@ static const struct regmap_config axi_adc_regmap_config = {
 	.max_register = 0x0800,
 };
 
+static const struct iio_backend_ops adi_axi_adc_generic = {
+	.enable = axi_adc_enable,
+	.disable = axi_adc_disable,
+	.data_format_set = axi_adc_data_format_set,
+	.chan_enable = axi_adc_chan_enable,
+	.chan_disable = axi_adc_chan_disable,
+	.request_buffer = axi_adc_request_buffer,
+	.free_buffer = axi_adc_free_buffer,
+};
+
 static int adi_axi_adc_probe(struct platform_device *pdev)
 {
-	struct adi_axi_adc_conv *conv;
-	struct iio_dev *indio_dev;
-	struct adi_axi_adc_client *cl;
 	struct adi_axi_adc_state *st;
 	void __iomem *base;
-	unsigned int ver;
+	unsigned int ver, *expected_ver;
 	int ret;
 
-	cl = adi_axi_adc_attach_client(&pdev->dev);
-	if (IS_ERR(cl))
-		return PTR_ERR(cl);
-
-	ret = devm_add_action_or_reset(&pdev->dev, adi_axi_adc_cleanup, cl);
-	if (ret)
-		return ret;
-
-	indio_dev = devm_iio_device_alloc(&pdev->dev, sizeof(*st));
-	if (indio_dev == NULL)
+	st = devm_kzalloc(&pdev->dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
 		return -ENOMEM;
 
-	st = iio_priv(indio_dev);
-	st->client = cl;
-	cl->state = st;
-	mutex_init(&st->lock);
-
 	base = devm_platform_ioremap_resource(pdev, 0);
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
+	st->dev = &pdev->dev;
 	st->regmap = devm_regmap_init_mmio(&pdev->dev, base,
 					   &axi_adc_regmap_config);
 	if (IS_ERR(st->regmap))
 		return PTR_ERR(st->regmap);
 
-	conv = &st->client->conv;
+	expected_ver = (unsigned int *)device_get_match_data(&pdev->dev);
+	if (!expected_ver)
+		return -ENODEV;
 
-	ret = axi_adc_reset(st);
+	/*
+	 * Force disable the core. Up to the frontend to enable us. And we can
+	 * still read/write registers...
+	 */
+	ret = regmap_write(st->regmap, ADI_AXI_REG_RSTN, 0);
 	if (ret)
 		return ret;
 
@@ -390,37 +205,23 @@ static int adi_axi_adc_probe(struct platform_device *pdev)
 	if (ret)
 		return ret;
 
-	if (cl->info->version > ver) {
+	if (*expected_ver > ver) {
 		dev_err(&pdev->dev,
 			"IP core version is too old. Expected %d.%.2d.%c, Reported %d.%.2d.%c\n",
-			ADI_AXI_PCORE_VER_MAJOR(cl->info->version),
-			ADI_AXI_PCORE_VER_MINOR(cl->info->version),
-			ADI_AXI_PCORE_VER_PATCH(cl->info->version),
+			ADI_AXI_PCORE_VER_MAJOR(*expected_ver),
+			ADI_AXI_PCORE_VER_MINOR(*expected_ver),
+			ADI_AXI_PCORE_VER_PATCH(*expected_ver),
 			ADI_AXI_PCORE_VER_MAJOR(ver),
 			ADI_AXI_PCORE_VER_MINOR(ver),
 			ADI_AXI_PCORE_VER_PATCH(ver));
 		return -ENODEV;
 	}
 
-	indio_dev->info = &adi_axi_adc_info;
-	indio_dev->name = "adi-axi-adc";
-	indio_dev->modes = INDIO_DIRECT_MODE;
-	indio_dev->num_channels = conv->chip_info->num_channels;
-	indio_dev->channels = conv->chip_info->channels;
-
-	ret = adi_axi_adc_config_dma_buffer(&pdev->dev, indio_dev);
+	ret = devm_iio_backend_register(&pdev->dev, &adi_axi_adc_generic, st);
 	if (ret)
 		return ret;
 
-	ret = adi_axi_adc_setup_channels(&pdev->dev, st);
-	if (ret)
-		return ret;
-
-	ret = devm_iio_device_register(&pdev->dev, indio_dev);
-	if (ret)
-		return ret;
-
-	dev_info(&pdev->dev, "AXI ADC IP core (%d.%.2d.%c) probed\n",
+	dev_info(&pdev->dev, "AXI ADC IP core (%d.%.2d.%d) probed\n",
 		 ADI_AXI_PCORE_VER_MAJOR(ver),
 		 ADI_AXI_PCORE_VER_MINOR(ver),
 		 ADI_AXI_PCORE_VER_PATCH(ver));
@@ -428,6 +229,8 @@ static int adi_axi_adc_probe(struct platform_device *pdev)
 	return 0;
 }
 
+static unsigned int adi_axi_adc_10_0_a_info = ADI_AXI_PCORE_VER(10, 0, 'a');
+
 /* Match table for of_platform binding */
 static const struct of_device_id adi_axi_adc_of_match[] = {
 	{ .compatible = "adi,axi-adc-10.0.a", .data = &adi_axi_adc_10_0_a_info },
@@ -448,3 +251,4 @@ MODULE_AUTHOR("Michael Hennerich <michael.hennerich@analog.com>");
 MODULE_DESCRIPTION("Analog Devices Generic AXI ADC IP core driver");
 MODULE_LICENSE("GPL v2");
 MODULE_IMPORT_NS(IIO_DMAENGINE_BUFFER);
+MODULE_IMPORT_NS(IIO_BACKEND);
diff --git a/include/linux/iio/adc/adi-axi-adc.h b/include/linux/iio/adc/adi-axi-adc.h
deleted file mode 100644
index b7904992d561..000000000000
--- a/include/linux/iio/adc/adi-axi-adc.h
+++ /dev/null
@@ -1,68 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-/*
- * Analog Devices Generic AXI ADC IP core driver/library
- * Link: https://wiki.analog.com/resources/fpga/docs/axi_adc_ip
- *
- * Copyright 2012-2020 Analog Devices Inc.
- */
-#ifndef __ADI_AXI_ADC_H__
-#define __ADI_AXI_ADC_H__
-
-struct device;
-struct iio_chan_spec;
-
-/**
- * struct adi_axi_adc_chip_info - Chip specific information
- * @name		Chip name
- * @id			Chip ID (usually product ID)
- * @channels		Channel specifications of type @struct iio_chan_spec
- * @num_channels	Number of @channels
- * @scale_table		Supported scales by the chip; tuples of 2 ints
- * @num_scales		Number of scales in the table
- * @max_rate		Maximum sampling rate supported by the device
- */
-struct adi_axi_adc_chip_info {
-	const char			*name;
-	unsigned int			id;
-
-	const struct iio_chan_spec	*channels;
-	unsigned int			num_channels;
-
-	const unsigned int		(*scale_table)[2];
-	int				num_scales;
-
-	unsigned long			max_rate;
-};
-
-/**
- * struct adi_axi_adc_conv - data of the ADC attached to the AXI ADC
- * @chip_info		chip info details for the client ADC
- * @preenable_setup	op to run in the client before enabling the AXI ADC
- * @reg_access		IIO debugfs_reg_access hook for the client ADC
- * @read_raw		IIO read_raw hook for the client ADC
- * @write_raw		IIO write_raw hook for the client ADC
- * @read_avail		IIO read_avail hook for the client ADC
- */
-struct adi_axi_adc_conv {
-	const struct adi_axi_adc_chip_info		*chip_info;
-
-	int (*preenable_setup)(struct adi_axi_adc_conv *conv);
-	int (*reg_access)(struct adi_axi_adc_conv *conv, unsigned int reg,
-			  unsigned int writeval, unsigned int *readval);
-	int (*read_raw)(struct adi_axi_adc_conv *conv,
-			struct iio_chan_spec const *chan,
-			int *val, int *val2, long mask);
-	int (*write_raw)(struct adi_axi_adc_conv *conv,
-			 struct iio_chan_spec const *chan,
-			 int val, int val2, long mask);
-	int (*read_avail)(struct adi_axi_adc_conv *conv,
-			  struct iio_chan_spec const *chan,
-			  const int **val, int *type, int *length, long mask);
-};
-
-struct adi_axi_adc_conv *devm_adi_axi_adc_conv_register(struct device *dev,
-							size_t sizeof_priv);
-
-void *adi_axi_adc_conv_priv(struct adi_axi_adc_conv *conv);
-
-#endif

-- 
2.43.0

Re: [PATCH v4 1/8] dt-bindings: adc: ad9467: add new io-backend property

[Rob Herring]

On Wed, 20 Dec 2023 16:34:04 +0100, Nuno Sa wrote:
> The ad9467 will make use of the new IIO backend framework which is a
> provider - consumer interface where IIO backends provide services to
> consumers. As such, and being this device a consumer,  add the new
> generic io-backend property to the bindings.
> 
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> ---
>  Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
> 

My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
on your patch (DT_CHECKER_FLAGS is new in v5.13):

yamllint warnings/errors:

dtschema/dtc warnings/errors:
/builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml: io-backends: missing type definition

doc reference errors (make refcheckdocs):

See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20231220-iio-backend-v4-1-998e9148b692@analog.com

The base for the series is generally the latest rc1. A different dependency
should be noted in *this* patch.

If you already ran 'make dt_binding_check' and didn't see the above
error(s), then make sure 'yamllint' is installed and dt-schema is up to
date:

pip3 install dtschema --upgrade

Please check and re-submit after running the above command yourself. Note
that DT_SCHEMA_FILES can be set to your schema file to speed up checking
your schema. However, it must be unset to test all examples with your schema.

Re: [PATCH v4 1/8] dt-bindings: adc: ad9467: add new io-backend property

[Jonathan Cameron]

On Wed, 20 Dec 2023 10:56:24 -0600
Rob Herring <robh@kernel.org> wrote:

> On Wed, 20 Dec 2023 16:34:04 +0100, Nuno Sa wrote:
> > The ad9467 will make use of the new IIO backend framework which is a
> > provider - consumer interface where IIO backends provide services to
> > consumers. As such, and being this device a consumer,  add the new
> > generic io-backend property to the bindings.
> > 
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > ---
> >  Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml | 4 ++++
> >  1 file changed, 4 insertions(+)
> >   
> 
> My bot found errors running 'make DT_CHECKER_FLAGS=-m dt_binding_check'
> on your patch (DT_CHECKER_FLAGS is new in v5.13):
> 
> yamllint warnings/errors:
> 
> dtschema/dtc warnings/errors:
> /builds/robherring/dt-review-ci/linux/Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml: io-backends: missing type definition

For reference this is expected as if this goes ahead that will be a dtschema addition.

> 
> doc reference errors (make refcheckdocs):
> 
> See https://patchwork.ozlabs.org/project/devicetree-bindings/patch/20231220-iio-backend-v4-1-998e9148b692@analog.com
> 
> The base for the series is generally the latest rc1. A different dependency
> should be noted in *this* patch.
> 
> If you already ran 'make dt_binding_check' and didn't see the above
> error(s), then make sure 'yamllint' is installed and dt-schema is up to
> date:
> 
> pip3 install dtschema --upgrade
> 
> Please check and re-submit after running the above command yourself. Note
> that DT_SCHEMA_FILES can be set to your schema file to speed up checking
> your schema. However, it must be unset to test all examples with your schema.
> 

Re: [PATCH v4 2/8] dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'

[Jonathan Cameron]

On Wed, 20 Dec 2023 16:34:05 +0100
Nuno Sa <nuno.sa@analog.com> wrote:

> 'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
> also remove it from being required.

With my 'specifications language' brain engaged (also know as pedantic)
I think this is a 'should' not a 'must' case. You aren't breaking
backwards compatibility just advising moving to the newer / better interface.


> 
> The reason why it's being deprecated is because the axi-adc CORE is now
> an IIO service provider hardware (IIO backends) for consumers to make use
> of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
> of consumer referencing other nodes/devices) and that proved to be wrong
> and to not scale.
> 
> Now, IIO consumers of this hardware are expected to reference it using the
> io-backends property.
> 
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> ---
>  Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> index 9996dd93f84b..835b40063343 100644
> --- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> +++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> @@ -39,12 +39,12 @@ properties:
>      $ref: /schemas/types.yaml#/definitions/phandle
>      description:
>        A reference to a the actual ADC to which this FPGA ADC interfaces to.
> +    deprecated: true
>  
>  required:
>    - compatible
>    - dmas
>    - reg
> -  - adi,adc-dev

Dropping it from required is fine, but do we have a new condition where one or the other
should be required?  If so good to add the dt-binding magic to enforce that. Look
for a oneOf combined with required. There are a few IIO examples of this either or
type required. You may want to then enforce that both are not provided though I
guess we perhaps don't care - the driver will just prioritise one approach over the other.

Jonathan


>  
>  additionalProperties: false
>  
> @@ -55,7 +55,5 @@ examples:
>          reg = <0x44a00000 0x10000>;
>          dmas = <&rx_dma 0>;
>          dma-names = "rx";
> -
> -        adi,adc-dev = <&spi_adc>;
>      };
>  ...
> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Jonathan Cameron]

On Wed, 20 Dec 2023 16:34:09 +0100
Nuno Sa <nuno.sa@analog.com> wrote:

> This is a Framework to handle complex IIO aggregate devices.
> 
> The typical architecture is to have one device as the frontend device which
> can be "linked" against one or multiple backend devices. All the IIO and
> userspace interface is expected to be registers/managed by the frontend
> device which will callback into the backends when needed (to get/set
> some configuration that it does not directly control).
> 
> The basic framework interface is pretty simple:
>  - Backends should register themselves with @devm_iio_backend_register()
>  - Frontend devices should get backends with @devm_iio_backend_get()
> 
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>

A few minor comments, but seems good to me otherwise.

Jonathan

> ---
>  MAINTAINERS                        |   8 +
>  drivers/iio/Kconfig                |   5 +
>  drivers/iio/Makefile               |   1 +
>  drivers/iio/industrialio-backend.c | 456 +++++++++++++++++++++++++++++++++++++
>  include/linux/iio/backend.h        |  75 ++++++
>  5 files changed, 545 insertions(+)
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 3029841e92a8..df5f5b988926 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -10334,6 +10334,14 @@ L:	linux-media@vger.kernel.org
>  S:	Maintained
>  F:	drivers/media/rc/iguanair.c
>  
> +IIO BACKEND FRAMEWORK
> +M:	Nuno Sa <nuno.sa@analog.com>
> +R:	Olivier Moysan <olivier.moysan@foss.st.com>
> +L:	linux-iio@vger.kernel.org
> +S:	Maintained
> +F:	drivers/iio/industrialio-backend.c
> +F:	include/linux/iio/backend.h
> +
>  IIO DIGITAL POTENTIOMETER DAC
>  M:	Peter Rosin <peda@axentia.se>
>  L:	linux-iio@vger.kernel.org
> diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> index 52eb46ef84c1..451671112f73 100644
> --- a/drivers/iio/Kconfig
> +++ b/drivers/iio/Kconfig
> @@ -71,6 +71,11 @@ config IIO_TRIGGERED_EVENT
>  	help
>  	  Provides helper functions for setting up triggered events.
>  
> +config IIO_BACKEND
> +	tristate
> +	help
> +	  Framework to handle complex IIO aggregate devices.

Add some more description here. Not sure the current text will help
anyone understand it :)

> +
>  source "drivers/iio/accel/Kconfig"
>  source "drivers/iio/adc/Kconfig"
>  source "drivers/iio/addac/Kconfig"
> diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> index 9622347a1c1b..0ba0e1521ba4 100644
> --- a/drivers/iio/Makefile
> +++ b/drivers/iio/Makefile
> @@ -13,6 +13,7 @@ obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o
>  obj-$(CONFIG_IIO_SW_DEVICE) += industrialio-sw-device.o
>  obj-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
>  obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
> +obj-$(CONFIG_IIO_BACKEND) += industrialio-backend.o
>  
>  obj-y += accel/
>  obj-y += adc/
> diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-backend.c
> new file mode 100644
> index 000000000000..75a0a66003e1
> --- /dev/null
> +++ b/drivers/iio/industrialio-backend.c
> @@ -0,0 +1,456 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Framework to handle complex IIO aggregate devices.
> + *
> + * The typical architecture is to have one device as the frontend device which
> + * can be "linked" against one or multiple backend devices. All the IIO and
> + * userspace interface is expected to be registers/managed by the frontend
> + * device which will callback into the backends when needed (to get/set some
> + * configuration that it does not directly control).
> + *
> + * The framework interface is pretty simple:
> + *   - Backends should register themselves with @devm_iio_backend_register()
> + *   - Frontend devices should get backends with @devm_iio_backend_get()
> + *
> + * Also to note that the primary target for this framework are converters like
> + * ADC/DACs so @iio_backend_ops will have some operations typical of converter
> + * devices. On top of that, this is "generic" for all IIO which means any kind
> + * of device can make use of the framework. That said, If the @iio_backend_ops
> + * struct begins to grow out of control, we can always refactor things so that
> + * the industrialio-backend.c is only left with the really generic stuff. Then,
> + * we can build on top of it depending on the needs.
> + *
> + * Copyright (C) 2023 Analog Devices Inc.
> + */
> +#define pr_fmt(fmt) "iio-backend: " fmt
> +
> +#include <linux/cleanup.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/list.h>
> +#include <linux/lockdep.h>
> +#include <linux/kref.h>
> +#include <linux/module.h>
> +#include <linux/mutex.h>
> +#include <linux/property.h>
> +#include <linux/slab.h>
> +
> +#include <linux/iio/backend.h>
> +
> +struct iio_backend {
> +	struct list_head entry;
> +	const struct iio_backend_ops *ops;
> +	struct device *dev;
> +	struct module *owner;
> +	void *priv;
> +	/*
> +	 * mutex used to synchronize backend callback access with concurrent
> +	 * calls to @iio_backend_unregister. The lock makes sure a device is
> +	 * not unregistered while a callback is being run.
> +	 */
> +	struct mutex lock;
> +	struct kref ref;
> +};
> +

...

> +
> +static void iio_backend_release(void *arg)
> +{
> +	struct iio_backend *back = arg;
> +
> +	module_put(back->owner);
> +	kref_put(&back->ref, iio_backend_free);
> +}
> +
> +static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
> +{
> +	struct device_link *link;
> +	int ret;
> +
> +	kref_get(&back->ref);
> +	if (!try_module_get(back->owner)) {
> +		pr_err("%s: Cannot get module reference\n", dev_name(dev));

Why do you need the reference?  Good to add a comment on that here.

> +		return -ENODEV;
> +	}
> +
> +	ret = devm_add_action_or_reset(dev, iio_backend_release, back);
> +	if (ret)
> +		return ret;
> +
> +	link = device_link_add(dev, back->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> +	if (!link)
> +		pr_warn("%s: Could not link to supplier(%s)\n", dev_name(dev),
> +			dev_name(back->dev));

Why is that not an error and we try to carry on?

> +
> +	pr_debug("%s: Found backend(%s) device\n", dev_name(dev),
> +		 dev_name(back->dev));
> +	return 0;
> +}
> +
> +/**
> + * devm_iio_backend_get - Get a backend device
> + * @dev:	Device where to look for the backend.
> + * @name:	Backend name.
> + *
> + * Get's the backend associated with @dev.
> + *
> + * RETURNS:
> + * A backend pointer, negative error pointer otherwise.
> + */
> +struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
> +{
> +	struct fwnode_handle *fwnode;
> +	struct iio_backend *back;
> +	int index = 0, ret;
> +
> +	if (name) {
> +		index = device_property_match_string(dev, "io-backends-names",
> +						     name);
> +		if (index < 0)
> +			return ERR_PTR(index);
> +	}
> +
> +	fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> +	if (IS_ERR(fwnode)) {
> +		/* not an error if optional */
> +		pr_debug("%s: Cannot get Firmware reference\n", dev_name(dev));
> +		return ERR_CAST(fwnode);
> +	}
> +
> +	guard(mutex)(&iio_back_lock);
> +	list_for_each_entry(back, &iio_back_list, entry) {
> +		if (!device_match_fwnode(back->dev, fwnode))
> +			continue;
> +
> +		fwnode_handle_put(fwnode);
> +		ret = __devm_iio_backend_get(dev, back);
> +		if (ret)
> +			return ERR_PTR(ret);
> +
> +		return back;
> +	}
> +
> +	fwnode_handle_put(fwnode);

FYI. I have a series doing auto cleanup of fwnode_handles in progress.
Should get some time over the weekend to snd that out.  Aim is to avoid need
to dance around manually freeing them (similar to the DT __free(device_node)
series I posted the other day).

> +	return ERR_PTR(-EPROBE_DEFER);
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, IIO_BACKEND);
> +
> +/**
> + * devm_iio_backend_get_optional - Get optional backend device
> + * @dev:	Device where to look for the backend.
> + * @name:	Backend name.
> + *
> + * Same as @devm_iio_backend_get() but return NULL if backend not found.
> + *
> + * RETURNS:
> + * A backend pointer, negative error pointer otherwise or NULL if not found.
> + */
> +struct iio_backend *devm_iio_backend_get_optional(struct device *dev,
> +						  const char *name)
> +{
> +	struct iio_backend *back;
> +
> +	back = devm_iio_backend_get(dev, name);
> +	if (IS_ERR(back) && PTR_ERR(back) == -ENOENT)
> +		return NULL;
> +
> +	return back;
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_optional, IIO_BACKEND);

I'm not convinced the optional variant is worth while.  Could just choose
a particular return value to mean that e.g. ERR_PTR(-ENOENT) and document
it for the normal get.  Then have special handling in the drivers where
you need backwards compatibility with a previous approach.

I'd rather pay the complexity price in a couple of drivers than have
to explain backends aren't typically optional for years to come.


> +
> +/**
> + * devm_iio_backend_get_from_fwnode_lookup
> + * @dev:	Device where to bind the backend lifetime.
> + * @fwnode:	Firmware node of the backend device.
> + *
> + * It directly looks the backend device list for a device matching @fwnode.

I would word this:
Search the backend list for a device matchign &fwnode.

> + * This API should not be used and it's only present for preventing the first
> + * user of this framework to break it's DT ABI.

You could stick a __ in front of the name to hopefully scare people away :)
+ highlight something odd is going on to reviewers seeing this called in
some future driver.
Also I can we might convert other drivers that are doing similar things
(dfsdm for example) and maybe this will be useful
so __devm_iio_backend_get_from_fwnode_lookup() and
"preventing breakage of old DT bindings".

> + *
> + * RETURNS:
> + * A backend pointer, negative error pointer otherwise.
> + */
> +struct iio_backend *
> +devm_iio_backend_get_from_fwnode_lookup(struct device *dev,
> +					struct fwnode_handle *fwnode)
> +{
> +	struct iio_backend *back;
> +	int ret;
> +
> +	guard(mutex)(&iio_back_lock);
> +	list_for_each_entry(back, &iio_back_list, entry) {
> +		if (!device_match_fwnode(back->dev, fwnode))
> +			continue;
> +
> +		ret = __devm_iio_backend_get(dev, back);
> +		if (ret)
> +			return ERR_PTR(ret);
> +
> +		return back;
> +	}
> +
> +	return ERR_PTR(-EPROBE_DEFER);
> +}
> +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_from_fwnode_lookup, IIO_BACKEND);

Re: [PATCH v4 7/8] iio: adc: ad9467: convert to backend framework

[Jonathan Cameron]

On Wed, 20 Dec 2023 16:34:10 +0100
Nuno Sa <nuno.sa@analog.com> wrote:

> Convert the driver to use the new IIO backend framework. The device
> functionality is expected to be the same (meaning no added or removed
> features).
> 
> Also note this patch effectively breaks ABI and that's needed so we can
> properly support this device and add needed features making use of the
> new IIO framework.
> 
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>

A few minor comments. Looks good to me.

Jonathan

> +static int ad9467_update_scan_mode(struct iio_dev *indio_dev,
> +				   const unsigned long *scan_mask)
> +{
> +	struct ad9467_state *st = iio_priv(indio_dev);
> +	unsigned int c;
> +	int ret;
> +
> +	for (c = 0; c < st->info->num_channels; c++) {
> +		if (test_bit(c, scan_mask))
> +			ret = iio_backend_chan_enable(st->back, c);
> +		else
> +			ret = iio_backend_chan_disable(st->back, c);
> +
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}

>  static int ad9467_reset(struct device *dev)
> @@ -443,25 +475,63 @@ static int ad9467_reset(struct device *dev)
>  	return 0;
>  }
>  
> +static int ad9467_iio_backend_get(struct ad9467_state *st)
> +{
> +	struct device *dev = &st->spi->dev;
> +	struct device_node *__back;
> +
> +	st->back = devm_iio_backend_get_optional(&st->spi->dev, NULL);
> +	if (IS_ERR(st->back))
> +		return PTR_ERR(st->back);

As per the comment on previous patch I'd just get it using the normal
function and handle PTR_ERR(-ENOENT) here as meaning we need to
try the old way.

> +	if (st->back)
> +		return 0;
> +	/*
> +	 * if we don't get the backend using the normal API's, use the legacy
> +	 * 'adi,adc-dev' property. So we get all nodes with that property, and
> +	 * look for the one pointing at us. Then we directly lookup that fwnode
> +	 * on the backend list of registered devices. This is done so we don't
> +	 * make io-backends mandatory which would break DT ABI.
> +	 */
> +	for_each_node_with_property(__back, "adi,adc-dev") {
> +		struct device_node *__me;
> +
> +		__me = of_parse_phandle(__back, "adi,adc-dev", 0);
> +		if (!__me)
> +			continue;
> +
> +		if (!device_match_of_node(dev, __me)) {
> +			of_node_put(__me);
> +			continue;
> +		}
> +
> +		of_node_put(__me);
> +		st->back = devm_iio_backend_get_from_fwnode_lookup(dev,
> +								   of_fwnode_handle(__back));
> +		of_node_put(__back);

If it lands first the patch
RFC PATCH 1/4] of: Add cleanup.h based autorelease via __free(device_node) markings.
will get rid of this manual handling for you for both the continue and return.
This will make a very nice example for that :)

> +		return PTR_ERR_OR_ZERO(st->back);
> +	}
> +
> +	return -ENODEV;
> +}

Re: [PATCH v4 1/8] dt-bindings: adc: ad9467: add new io-backend property

[Rob Herring]

On Wed, 20 Dec 2023 16:34:04 +0100, Nuno Sa wrote:
> The ad9467 will make use of the new IIO backend framework which is a
> provider - consumer interface where IIO backends provide services to
> consumers. As such, and being this device a consumer,  add the new
> generic io-backend property to the bindings.
> 
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> ---
>  Documentation/devicetree/bindings/iio/adc/adi,ad9467.yaml | 4 ++++
>  1 file changed, 4 insertions(+)
> 

Reviewed-by: Rob Herring <robh@kernel.org>

Re: [PATCH v4 4/8] of: property: add device link support for io-backends

[Rob Herring]

On Wed, 20 Dec 2023 16:34:07 +0100, Nuno Sa wrote:
> From: Olivier Moysan <olivier.moysan@foss.st.com>
> 
> Add support for creating device links out of more DT properties.
> 
> Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> ---
>  drivers/of/property.c | 2 ++
>  1 file changed, 2 insertions(+)
> 

Acked-by: Rob Herring <robh@kernel.org>

Re: [PATCH v4 2/8] dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'

[Nuno Sá]

On Thu, 2023-12-21 at 17:25 +0000, Jonathan Cameron wrote:
> On Wed, 20 Dec 2023 16:34:05 +0100
> Nuno Sa <nuno.sa@analog.com> wrote:
> 
> > 'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
> > also remove it from being required.
> 
> With my 'specifications language' brain engaged (also know as pedantic)
> I think this is a 'should' not a 'must' case. You aren't breaking
> backwards compatibility just advising moving to the newer / better interface.
> 

Well, you surely know better than me as a native speaker :)

> 
> > 
> > The reason why it's being deprecated is because the axi-adc CORE is now
> > an IIO service provider hardware (IIO backends) for consumers to make use
> > of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
> > of consumer referencing other nodes/devices) and that proved to be wrong
> > and to not scale.
> > 
> > Now, IIO consumers of this hardware are expected to reference it using the
> > io-backends property.
> > 
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > ---
> >  Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 4 +---
> >  1 file changed, 1 insertion(+), 3 deletions(-)
> > 
> > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > index 9996dd93f84b..835b40063343 100644
> > --- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > +++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > @@ -39,12 +39,12 @@ properties:
> >      $ref: /schemas/types.yaml#/definitions/phandle
> >      description:
> >        A reference to a the actual ADC to which this FPGA ADC interfaces to.
> > +    deprecated: true
> >  
> >  required:
> >    - compatible
> >    - dmas
> >    - reg
> > -  - adi,adc-dev
> 
> Dropping it from required is fine, but do we have a new condition where one or the
> other
> should be required?  If so good to add the dt-binding magic to enforce that. Look
> for a oneOf combined with required. There are a few IIO examples of this either or
> type required. You may want to then enforce that both are not provided though I
> guess we perhaps don't care - the driver will just prioritise one approach over the
> other.
> 

Hmm, the thing is that io-backends is applied in the frontend device (so other
binding) and in here we should only have the adi,adc-dev which is now deprecated so
I'm not sure how that would look like?

I think new users of the deprecated property are very unlikely unless they choose to
ignore the deprecated warning. As for old users (if they add the new one and don't
remove this one, the new one will have priority). But I'm still confident there are
no users of this out there :)


- Nuno Sá

Re: [PATCH v4 7/8] iio: adc: ad9467: convert to backend framework

[Nuno Sá]

On Thu, 2023-12-21 at 17:52 +0000, Jonathan Cameron wrote:
> On Wed, 20 Dec 2023 16:34:10 +0100
> Nuno Sa <nuno.sa@analog.com> wrote:
> 
> > Convert the driver to use the new IIO backend framework. The device
> > functionality is expected to be the same (meaning no added or removed
> > features).
> > 
> > Also note this patch effectively breaks ABI and that's needed so we can
> > properly support this device and add needed features making use of the
> > new IIO framework.
> > 
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> A few minor comments. Looks good to me.
> 
> Jonathan
> 
> > +static int ad9467_update_scan_mode(struct iio_dev *indio_dev,
> > +                                  const unsigned long *scan_mask)
> > +{
> > +       struct ad9467_state *st = iio_priv(indio_dev);
> > +       unsigned int c;
> > +       int ret;
> > +
> > +       for (c = 0; c < st->info->num_channels; c++) {
> > +               if (test_bit(c, scan_mask))
> > +                       ret = iio_backend_chan_enable(st->back, c);
> > +               else
> > +                       ret = iio_backend_chan_disable(st->back, c);
> > +
> > +               if (ret)
> > +                       return ret;
> > +       }
> > +
> > +       return 0;
> > +}
> 
> >  static int ad9467_reset(struct device *dev)
> > @@ -443,25 +475,63 @@ static int ad9467_reset(struct device *dev)
> >         return 0;
> >  }
> >  
> > +static int ad9467_iio_backend_get(struct ad9467_state *st)
> > +{
> > +       struct device *dev = &st->spi->dev;
> > +       struct device_node *__back;
> > +
> > +       st->back = devm_iio_backend_get_optional(&st->spi->dev, NULL);
> > +       if (IS_ERR(st->back))
> > +               return PTR_ERR(st->back);
> 
> As per the comment on previous patch I'd just get it using the normal
> function and handle PTR_ERR(-ENOENT) here as meaning we need to
> try the old way.

That makes sense. So we can add a devm_iio_backend_get_optional() API when/if we
really need one and not just for handling legacy code.

> 
> > +       if (st->back)
> > +               return 0;
> > +       /*
> > +        * if we don't get the backend using the normal API's, use the legacy
> > +        * 'adi,adc-dev' property. So we get all nodes with that property, and
> > +        * look for the one pointing at us. Then we directly lookup that fwnode
> > +        * on the backend list of registered devices. This is done so we don't
> > +        * make io-backends mandatory which would break DT ABI.
> > +        */
> > +       for_each_node_with_property(__back, "adi,adc-dev") {
> > +               struct device_node *__me;
> > +
> > +               __me = of_parse_phandle(__back, "adi,adc-dev", 0);
> > +               if (!__me)
> > +                       continue;
> > +
> > +               if (!device_match_of_node(dev, __me)) {
> > +                       of_node_put(__me);
> > +                       continue;
> > +               }
> > +
> > +               of_node_put(__me);
> > +               st->back = devm_iio_backend_get_from_fwnode_lookup(dev,
> > +                                                                 
> > of_fwnode_handle(__back));
> > +               of_node_put(__back);
> 
> If it lands first the patch
> RFC PATCH 1/4] of: Add cleanup.h based autorelease via __free(device_node)
> markings.
> will get rid of this manual handling for you for both the continue and return.
> This will make a very nice example for that :)

Yeah, and I'll happily rebase on that...

- Nuno Sá
> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Nuno Sá]

On Thu, 2023-12-21 at 17:44 +0000, Jonathan Cameron wrote:
> On Wed, 20 Dec 2023 16:34:09 +0100
> Nuno Sa <nuno.sa@analog.com> wrote:
> 
> > This is a Framework to handle complex IIO aggregate devices.
> > 
> > The typical architecture is to have one device as the frontend device which
> > can be "linked" against one or multiple backend devices. All the IIO and
> > userspace interface is expected to be registers/managed by the frontend
> > device which will callback into the backends when needed (to get/set
> > some configuration that it does not directly control).
> > 
> > The basic framework interface is pretty simple:
> >  - Backends should register themselves with @devm_iio_backend_register()
> >  - Frontend devices should get backends with @devm_iio_backend_get()
> > 
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> 
> A few minor comments, but seems good to me otherwise.
> 
> Jonathan
> 
> > ---
> >  MAINTAINERS                        |   8 +
> >  drivers/iio/Kconfig                |   5 +
> >  drivers/iio/Makefile               |   1 +
> >  drivers/iio/industrialio-backend.c | 456 +++++++++++++++++++++++++++++++++++++
> >  include/linux/iio/backend.h        |  75 ++++++
> >  5 files changed, 545 insertions(+)
> > 
> > diff --git a/MAINTAINERS b/MAINTAINERS
> > index 3029841e92a8..df5f5b988926 100644
> > --- a/MAINTAINERS
> > +++ b/MAINTAINERS
> > @@ -10334,6 +10334,14 @@ L:     linux-media@vger.kernel.org
> >  S:     Maintained
> >  F:     drivers/media/rc/iguanair.c
> >  
> > +IIO BACKEND FRAMEWORK
> > +M:     Nuno Sa <nuno.sa@analog.com>
> > +R:     Olivier Moysan <olivier.moysan@foss.st.com>
> > +L:     linux-iio@vger.kernel.org
> > +S:     Maintained
> > +F:     drivers/iio/industrialio-backend.c
> > +F:     include/linux/iio/backend.h
> > +
> >  IIO DIGITAL POTENTIOMETER DAC
> >  M:     Peter Rosin <peda@axentia.se>
> >  L:     linux-iio@vger.kernel.org
> > diff --git a/drivers/iio/Kconfig b/drivers/iio/Kconfig
> > index 52eb46ef84c1..451671112f73 100644
> > --- a/drivers/iio/Kconfig
> > +++ b/drivers/iio/Kconfig
> > @@ -71,6 +71,11 @@ config IIO_TRIGGERED_EVENT
> >         help
> >           Provides helper functions for setting up triggered events.
> >  
> > +config IIO_BACKEND
> > +       tristate
> > +       help
> > +         Framework to handle complex IIO aggregate devices.
> 
> Add some more description here. Not sure the current text will help
> anyone understand it :)
> 

Alright...

> > +
> >  source "drivers/iio/accel/Kconfig"
> >  source "drivers/iio/adc/Kconfig"
> >  source "drivers/iio/addac/Kconfig"
> > diff --git a/drivers/iio/Makefile b/drivers/iio/Makefile
> > index 9622347a1c1b..0ba0e1521ba4 100644
> > --- a/drivers/iio/Makefile
> > +++ b/drivers/iio/Makefile
> > @@ -13,6 +13,7 @@ obj-$(CONFIG_IIO_GTS_HELPER) += industrialio-gts-helper.o
> >  obj-$(CONFIG_IIO_SW_DEVICE) += industrialio-sw-device.o
> >  obj-$(CONFIG_IIO_SW_TRIGGER) += industrialio-sw-trigger.o
> >  obj-$(CONFIG_IIO_TRIGGERED_EVENT) += industrialio-triggered-event.o
> > +obj-$(CONFIG_IIO_BACKEND) += industrialio-backend.o
> >  
> >  obj-y += accel/
> >  obj-y += adc/
> > diff --git a/drivers/iio/industrialio-backend.c b/drivers/iio/industrialio-
> > backend.c
> > new file mode 100644
> > index 000000000000..75a0a66003e1
> > --- /dev/null
> > +++ b/drivers/iio/industrialio-backend.c
> > @@ -0,0 +1,456 @@
> > +// SPDX-License-Identifier: GPL-2.0-only
> > +/*
> > + * Framework to handle complex IIO aggregate devices.
> > + *
> > + * The typical architecture is to have one device as the frontend device which
> > + * can be "linked" against one or multiple backend devices. All the IIO and
> > + * userspace interface is expected to be registers/managed by the frontend
> > + * device which will callback into the backends when needed (to get/set some
> > + * configuration that it does not directly control).
> > + *
> > + * The framework interface is pretty simple:
> > + *   - Backends should register themselves with @devm_iio_backend_register()
> > + *   - Frontend devices should get backends with @devm_iio_backend_get()
> > + *
> > + * Also to note that the primary target for this framework are converters like
> > + * ADC/DACs so @iio_backend_ops will have some operations typical of converter
> > + * devices. On top of that, this is "generic" for all IIO which means any kind
> > + * of device can make use of the framework. That said, If the @iio_backend_ops
> > + * struct begins to grow out of control, we can always refactor things so that
> > + * the industrialio-backend.c is only left with the really generic stuff. Then,
> > + * we can build on top of it depending on the needs.
> > + *
> > + * Copyright (C) 2023 Analog Devices Inc.
> > + */
> > +#define pr_fmt(fmt) "iio-backend: " fmt
> > +
> > +#include <linux/cleanup.h>
> > +#include <linux/device.h>
> > +#include <linux/err.h>
> > +#include <linux/list.h>
> > +#include <linux/lockdep.h>
> > +#include <linux/kref.h>
> > +#include <linux/module.h>
> > +#include <linux/mutex.h>
> > +#include <linux/property.h>
> > +#include <linux/slab.h>
> > +
> > +#include <linux/iio/backend.h>
> > +
> > +struct iio_backend {
> > +       struct list_head entry;
> > +       const struct iio_backend_ops *ops;
> > +       struct device *dev;
> > +       struct module *owner;
> > +       void *priv;
> > +       /*
> > +        * mutex used to synchronize backend callback access with concurrent
> > +        * calls to @iio_backend_unregister. The lock makes sure a device is
> > +        * not unregistered while a callback is being run.
> > +        */
> > +       struct mutex lock;
> > +       struct kref ref;
> > +};
> > +
> 
> ...
> 
> > +
> > +static void iio_backend_release(void *arg)
> > +{
> > +       struct iio_backend *back = arg;
> > +
> > +       module_put(back->owner);
> > +       kref_put(&back->ref, iio_backend_free);
> > +}
> > +
> > +static int __devm_iio_backend_get(struct device *dev, struct iio_backend *back)
> > +{
> > +       struct device_link *link;
> > +       int ret;
> > +
> > +       kref_get(&back->ref);
> > +       if (!try_module_get(back->owner)) {
> > +               pr_err("%s: Cannot get module reference\n", dev_name(dev));
> 
> Why do you need the reference?  Good to add a comment on that here.

Yeah, typical stuff when it's a module and we don't want for it to go away. Even
though we handle that case with pointer stuff. I'll comment it.

> 
> > +               return -ENODEV;
> > +       }
> > +
> > +       ret = devm_add_action_or_reset(dev, iio_backend_release, back);
> > +       if (ret)
> > +               return ret;
> > +
> > +       link = device_link_add(dev, back->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > +       if (!link)
> > +               pr_warn("%s: Could not link to supplier(%s)\n", dev_name(dev),
> > +                       dev_name(back->dev));
> 
> Why is that not an error and we try to carry on?

I guess having the links are not really mandatory for the whole thing to work (more
like a nice to have). That's also how this is handled in another subsystems so I
figured it would be fine.

But since you are speaking about this... After you pointing me to Bartosz's talk and
sawing it (as stuff like this is mentioned), I started to question this. The goal
with the above comment is that if you remove the backend, all the consumers are
automatically removed (unbound). Just not sure if that's what we always want (and we
are already handling the situation where a backend goes away with -ENODEV) as some
frontends could still be useful without the backend (I guess that could be
plausible). I think for now we don't really have such usecases so the links can make
sense (and we can figure something like optionally creating these links if we ever
need too) but having your inputs on this will definitely be valuable.

> > +
> > +       pr_debug("%s: Found backend(%s) device\n", dev_name(dev),
> > +                dev_name(back->dev));
> > +       return 0;
> > +}
> > +
> > +/**
> > + * devm_iio_backend_get - Get a backend device
> > + * @dev:       Device where to look for the backend.
> > + * @name:      Backend name.
> > + *
> > + * Get's the backend associated with @dev.
> > + *
> > + * RETURNS:
> > + * A backend pointer, negative error pointer otherwise.
> > + */
> > +struct iio_backend *devm_iio_backend_get(struct device *dev, const char *name)
> > +{
> > +       struct fwnode_handle *fwnode;
> > +       struct iio_backend *back;
> > +       int index = 0, ret;
> > +
> > +       if (name) {
> > +               index = device_property_match_string(dev, "io-backends-names",
> > +                                                    name);
> > +               if (index < 0)
> > +                       return ERR_PTR(index);
> > +       }
> > +
> > +       fwnode = fwnode_find_reference(dev_fwnode(dev), "io-backends", index);
> > +       if (IS_ERR(fwnode)) {
> > +               /* not an error if optional */
> > +               pr_debug("%s: Cannot get Firmware reference\n", dev_name(dev));
> > +               return ERR_CAST(fwnode);
> > +       }
> > +
> > +       guard(mutex)(&iio_back_lock);
> > +       list_for_each_entry(back, &iio_back_list, entry) {
> > +               if (!device_match_fwnode(back->dev, fwnode))
> > +                       continue;
> > +
> > +               fwnode_handle_put(fwnode);
> > +               ret = __devm_iio_backend_get(dev, back);
> > +               if (ret)
> > +                       return ERR_PTR(ret);
> > +
> > +               return back;
> > +       }
> > +
> > +       fwnode_handle_put(fwnode);
> 
> FYI. I have a series doing auto cleanup of fwnode_handles in progress.
> Should get some time over the weekend to snd that out.  Aim is to avoid need
> to dance around manually freeing them (similar to the DT __free(device_node)
> series I posted the other day).

Cool! This will surely be an user of that.

> 
> > +       return ERR_PTR(-EPROBE_DEFER);
> > +}
> > +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get, IIO_BACKEND);
> > +
> > +/**
> > + * devm_iio_backend_get_optional - Get optional backend device
> > + * @dev:       Device where to look for the backend.
> > + * @name:      Backend name.
> > + *
> > + * Same as @devm_iio_backend_get() but return NULL if backend not found.
> > + *
> > + * RETURNS:
> > + * A backend pointer, negative error pointer otherwise or NULL if not found.
> > + */
> > +struct iio_backend *devm_iio_backend_get_optional(struct device *dev,
> > +                                                 const char *name)
> > +{
> > +       struct iio_backend *back;
> > +
> > +       back = devm_iio_backend_get(dev, name);
> > +       if (IS_ERR(back) && PTR_ERR(back) == -ENOENT)
> > +               return NULL;
> > +
> > +       return back;
> > +}
> > +EXPORT_SYMBOL_NS_GPL(devm_iio_backend_get_optional, IIO_BACKEND);
> 
> I'm not convinced the optional variant is worth while.  Could just choose
> a particular return value to mean that e.g. ERR_PTR(-ENOENT) and document
> it for the normal get.  Then have special handling in the drivers where
> you need backwards compatibility with a previous approach.
> 
> I'd rather pay the complexity price in a couple of drivers than have
> to explain backends aren't typically optional for years to come.

Alright. For now I'm not seeing any usecase where backends are optional. For the case
we need the backward compatibility I'll do as you suggest. If we ever have a real
'optional' usecase we can easily add this one again.

> 
> 
> > +
> > +/**
> > + * devm_iio_backend_get_from_fwnode_lookup
> > + * @dev:       Device where to bind the backend lifetime.
> > + * @fwnode:    Firmware node of the backend device.
> > + *
> > + * It directly looks the backend device list for a device matching @fwnode.
> 
> I would word this:
> Search the backend list for a device matchign &fwnode.

ack

> 
> > + * This API should not be used and it's only present for preventing the first
> > + * user of this framework to break it's DT ABI.
> 
> You could stick a __ in front of the name to hopefully scare people away :)
> + highlight something odd is going on to reviewers seeing this called in
> some future driver.
> Also I can we might convert other drivers that are doing similar things
> (dfsdm for example) and maybe this will be useful
> so __devm_iio_backend_get_from_fwnode_lookup() and
> "preventing breakage of old DT bindings".

Will do!

Thanks for the inputs!
- Nuno Sá

Re: [PATCH v4 2/8] dt-bindings: adc: axi-adc: deprecate 'adi,adc-dev'

[Jonathan Cameron]

On Fri, 22 Dec 2023 10:07:34 +0100
Nuno Sá <noname.nuno@gmail.com> wrote:

> On Thu, 2023-12-21 at 17:25 +0000, Jonathan Cameron wrote:
> > On Wed, 20 Dec 2023 16:34:05 +0100
> > Nuno Sa <nuno.sa@analog.com> wrote:
> >   
> > > 'adi,adc-dev' is now deprecated and must not be used anymore. Hence,
> > > also remove it from being required.  
> > 
> > With my 'specifications language' brain engaged (also know as pedantic)
> > I think this is a 'should' not a 'must' case. You aren't breaking
> > backwards compatibility just advising moving to the newer / better interface.
> >   
> 
> Well, you surely know better than me as a native speaker :)
> 
> >   
> > > 
> > > The reason why it's being deprecated is because the axi-adc CORE is now
> > > an IIO service provider hardware (IIO backends) for consumers to make use
> > > of. Before, the logic with 'adi,adc-dev' was the opposite (it was kind
> > > of consumer referencing other nodes/devices) and that proved to be wrong
> > > and to not scale.
> > > 
> > > Now, IIO consumers of this hardware are expected to reference it using the
> > > io-backends property.
> > > 
> > > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > > ---
> > >  Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml | 4 +---
> > >  1 file changed, 1 insertion(+), 3 deletions(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > > b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > > index 9996dd93f84b..835b40063343 100644
> > > --- a/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > > +++ b/Documentation/devicetree/bindings/iio/adc/adi,axi-adc.yaml
> > > @@ -39,12 +39,12 @@ properties:
> > >      $ref: /schemas/types.yaml#/definitions/phandle
> > >      description:
> > >        A reference to a the actual ADC to which this FPGA ADC interfaces to.
> > > +    deprecated: true
> > >  
> > >  required:
> > >    - compatible
> > >    - dmas
> > >    - reg
> > > -  - adi,adc-dev  
> > 
> > Dropping it from required is fine, but do we have a new condition where one or the
> > other
> > should be required?  If so good to add the dt-binding magic to enforce that. Look
> > for a oneOf combined with required. There are a few IIO examples of this either or
> > type required. You may want to then enforce that both are not provided though I
> > guess we perhaps don't care - the driver will just prioritise one approach over the
> > other.
> >   
> 
> Hmm, the thing is that io-backends is applied in the frontend device (so other
> binding) and in here we should only have the adi,adc-dev which is now deprecated so
> I'm not sure how that would look like?

Ah. I'd somehow failed to register the property is now in the other device. 
Not much we can do then :(

> 
> I think new users of the deprecated property are very unlikely unless they choose to
> ignore the deprecated warning. As for old users (if they add the new one and don't
> remove this one, the new one will have priority). But I'm still confident there are
> no users of this out there :(

Sometimes it's easier to cater for non existent users than get into too much
debate on whether they exist :)

Jonathan

> 
> 
> - Nuno Sá
> 
> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Jonathan Cameron]

> > > +
> > > +       ret = devm_add_action_or_reset(dev, iio_backend_release, back);
> > > +       if (ret)
> > > +               return ret;
> > > +
> > > +       link = device_link_add(dev, back->dev, DL_FLAG_AUTOREMOVE_CONSUMER);
> > > +       if (!link)
> > > +               pr_warn("%s: Could not link to supplier(%s)\n", dev_name(dev),
> > > +                       dev_name(back->dev));  
> > 
> > Why is that not an error and we try to carry on?  
> 
> I guess having the links are not really mandatory for the whole thing to work (more
> like a nice to have). That's also how this is handled in another subsystems so I
> figured it would be fine.
> 
> But since you are speaking about this... After you pointing me to Bartosz's talk and
> sawing it (as stuff like this is mentioned), I started to question this. The goal
> with the above comment is that if you remove the backend, all the consumers are
> automatically removed (unbound). Just not sure if that's what we always want (and we
> are already handling the situation where a backend goes away with -ENODEV) as some
> frontends could still be useful without the backend (I guess that could be
> plausible). I think for now we don't really have such usecases so the links can make
> sense (and we can figure something like optionally creating these links if we ever
> need too) but having your inputs on this will definitely be valuable.

I'm not keen on both trying to make everything tear down cleanly AND making sure
it all works even if we don't. That just adds two code paths to test when either
should be sufficient on its own.  I don't really mind which.  Bartosz's stuff
is nice, but it may not be the right solution here. 

> 
> > > +
> > > +       pr_debug("%s: Found backend(%s) device\n", dev_name(dev),
> > > +                dev_name(back->dev));
> > > +       return 0;
> > > +}
> > > +

Jonathan

Re: [PATCH v4 4/8] of: property: add device link support for io-backends

[David Lechner]

On Wed, Dec 20, 2023 at 9:32 AM Nuno Sa <nuno.sa@analog.com> wrote:
>
> From: Olivier Moysan <olivier.moysan@foss.st.com>
>
> Add support for creating device links out of more DT properties.
>
> Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
> Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> ---
>  drivers/of/property.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/drivers/of/property.c b/drivers/of/property.c
> index afdaefbd03f6..a4835447759f 100644
> --- a/drivers/of/property.c
> +++ b/drivers/of/property.c
> @@ -1244,6 +1244,7 @@ DEFINE_SIMPLE_PROP(interconnects, "interconnects", "#interconnect-cells")
>  DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
>  DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
>  DEFINE_SIMPLE_PROP(io_channels, "io-channel", "#io-channel-cells")
> +DEFINE_SIMPLE_PROP(io_backends, "io-backends", NULL)

In v3 it was agreed that adding #io-backend-cells right way seemed
like a good idea. Do we need to include that here?

>  DEFINE_SIMPLE_PROP(interrupt_parent, "interrupt-parent", NULL)
>  DEFINE_SIMPLE_PROP(dmas, "dmas", "#dma-cells")
>  DEFINE_SIMPLE_PROP(power_domains, "power-domains", "#power-domain-cells")
> @@ -1334,6 +1335,7 @@ static const struct supplier_bindings of_supplier_bindings[] = {
>         { .parse_prop = parse_iommu_maps, .optional = true, },
>         { .parse_prop = parse_mboxes, },
>         { .parse_prop = parse_io_channels, },
> +       { .parse_prop = parse_io_backends, },
>         { .parse_prop = parse_interrupt_parent, },
>         { .parse_prop = parse_dmas, .optional = true, },
>         { .parse_prop = parse_power_domains, },
>
> --
> 2.43.0
>
>

Re: [PATCH v4 4/8] of: property: add device link support for io-backends

[Nuno Sá]

On Wed, 2024-01-03 at 15:39 -0600, David Lechner wrote:
> On Wed, Dec 20, 2023 at 9:32 AM Nuno Sa <nuno.sa@analog.com> wrote:
> > 
> > From: Olivier Moysan <olivier.moysan@foss.st.com>
> > 
> > Add support for creating device links out of more DT properties.
> > 
> > Signed-off-by: Olivier Moysan <olivier.moysan@foss.st.com>
> > Signed-off-by: Nuno Sa <nuno.sa@analog.com>
> > ---
> >  drivers/of/property.c | 2 ++
> >  1 file changed, 2 insertions(+)
> > 
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index afdaefbd03f6..a4835447759f 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1244,6 +1244,7 @@ DEFINE_SIMPLE_PROP(interconnects, "interconnects",
> > "#interconnect-cells")
> >  DEFINE_SIMPLE_PROP(iommus, "iommus", "#iommu-cells")
> >  DEFINE_SIMPLE_PROP(mboxes, "mboxes", "#mbox-cells")
> >  DEFINE_SIMPLE_PROP(io_channels, "io-channel", "#io-channel-cells")
> > +DEFINE_SIMPLE_PROP(io_backends, "io-backends", NULL)
> 
> In v3 it was agreed that adding #io-backend-cells right way seemed
> like a good idea. Do we need to include that here?
> 

Yeah that's something I forgot and should do in v5. Should also update the core
code and the backend bindings (axi-adc) to have it (one of Rob's points in
having the #cells was to easily identify backends - providers).

Thanks for spotting this!
- Nuno Sá

> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Nuno Sá]

On Tue, 2023-12-26 at 15:59 +0000, Jonathan Cameron wrote:
> 
> > > > +
> > > > +       ret = devm_add_action_or_reset(dev, iio_backend_release, back);
> > > > +       if (ret)
> > > > +               return ret;
> > > > +
> > > > +       link = device_link_add(dev, back->dev,
> > > > DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > +       if (!link)
> > > > +               pr_warn("%s: Could not link to supplier(%s)\n",
> > > > dev_name(dev),
> > > > +                       dev_name(back->dev));  
> > > 
> > > Why is that not an error and we try to carry on?  
> > 
> > I guess having the links are not really mandatory for the whole thing to
> > work (more
> > like a nice to have). That's also how this is handled in another subsystems
> > so I
> > figured it would be fine.
> > 
> > But since you are speaking about this... After you pointing me to Bartosz's
> > talk and
> > sawing it (as stuff like this is mentioned), I started to question this. The
> > goal
> > with the above comment is that if you remove the backend, all the consumers
> > are
> > automatically removed (unbound). Just not sure if that's what we always want
> > (and we
> > are already handling the situation where a backend goes away with -ENODEV)
> > as some
> > frontends could still be useful without the backend (I guess that could be
> > plausible). I think for now we don't really have such usecases so the links
> > can make
> > sense (and we can figure something like optionally creating these links if
> > we ever
> > need too) but having your inputs on this will definitely be valuable.
> 
> I'm not keen on both trying to make everything tear down cleanly AND making
> sure
> it all works even if we don't. That just adds two code paths to test when
> either
> should be sufficient on its own.  I don't really mind which.  Bartosz's stuff

Agreed...

> is nice, but it may not be the right solution here. 

There's pros and cons on both options... 

For the device links the cons I see is that it depends on patch 3 for it to work
(or some other approach if the one in that patch is not good) - not really a
real con though :). The biggest concern is (possible) future uses where we end
up with cases where removing a backend is not really a "deal breaker". I could
think of frontends that have multiple backends (one per data path) and removing
one backend would not tear the whole thing down (we would just have one non
functional data paths/port where the others are still ok).

Olivier, for STM usecases, do we always need the backend? I mean, does it make
sense to always remove/unbind the frontend in case the backend is unbound?

Maybe some of your usecases already "forces" us with a decision. 

The biggest pro I see is code simplicity. If we can assume the frontend can
never exist in case one of the backends is gone, we can:

 * get rid of the sync mutex;
 * get rid of the kref and bind the backend object lifetime to the backend
device (using devm_kzalloc() instead of kzalloc + refcount.

Basically, we would not need to care about syncing the backend existence with
accessing it...
To sum up, the device_links approach tends to be similar (not identical) to the
previous approach using the component API.

The biggest pro I see in Bartosz's stuff is flexibility. So it should just work
in whatever future usecases we might have. I fear that going the device_links
road we might end up needing this stuff anyways.

Obviously, the biggest con is code complexity (not that bad though) as we always
need to properly sync any backend callback.

- Nuno Sá
> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Jonathan Cameron]

On Tue, 09 Jan 2024 13:15:54 +0100
Nuno Sá <noname.nuno@gmail.com> wrote:

> On Tue, 2023-12-26 at 15:59 +0000, Jonathan Cameron wrote:
> >   
> > > > > +
> > > > > +       ret = devm_add_action_or_reset(dev, iio_backend_release, back);
> > > > > +       if (ret)
> > > > > +               return ret;
> > > > > +
> > > > > +       link = device_link_add(dev, back->dev,
> > > > > DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > > +       if (!link)
> > > > > +               pr_warn("%s: Could not link to supplier(%s)\n",
> > > > > dev_name(dev),
> > > > > +                       dev_name(back->dev));    
> > > > 
> > > > Why is that not an error and we try to carry on?    
> > > 
> > > I guess having the links are not really mandatory for the whole thing to
> > > work (more
> > > like a nice to have). That's also how this is handled in another subsystems
> > > so I
> > > figured it would be fine.
> > > 
> > > But since you are speaking about this... After you pointing me to Bartosz's
> > > talk and
> > > sawing it (as stuff like this is mentioned), I started to question this. The
> > > goal
> > > with the above comment is that if you remove the backend, all the consumers
> > > are
> > > automatically removed (unbound). Just not sure if that's what we always want
> > > (and we
> > > are already handling the situation where a backend goes away with -ENODEV)
> > > as some
> > > frontends could still be useful without the backend (I guess that could be
> > > plausible). I think for now we don't really have such usecases so the links
> > > can make
> > > sense (and we can figure something like optionally creating these links if
> > > we ever
> > > need too) but having your inputs on this will definitely be valuable.  
> > 
> > I'm not keen on both trying to make everything tear down cleanly AND making
> > sure
> > it all works even if we don't. That just adds two code paths to test when
> > either
> > should be sufficient on its own.  I don't really mind which.  Bartosz's stuff  
> 
> Agreed...
> 
> > is nice, but it may not be the right solution here.   
> 
> There's pros and cons on both options... 
> 
> For the device links the cons I see is that it depends on patch 3 for it to work
> (or some other approach if the one in that patch is not good) - not really a
> real con though :). The biggest concern is (possible) future uses where we end
> up with cases where removing a backend is not really a "deal breaker". I could
> think of frontends that have multiple backends (one per data path) and removing
> one backend would not tear the whole thing down (we would just have one non
> functional data paths/port where the others are still ok).

I wouldn't waste time catering to such set ups.  If the whole thing gets
torn down because one element went away that should be fine.
To do anything else I'd want to see a real world use case.

> 
> Olivier, for STM usecases, do we always need the backend? I mean, does it make
> sense to always remove/unbind the frontend in case the backend is unbound?
> 
> Maybe some of your usecases already "forces" us with a decision. 
> 
> The biggest pro I see is code simplicity. If we can assume the frontend can
> never exist in case one of the backends is gone, we can:
> 
>  * get rid of the sync mutex;
>  * get rid of the kref and bind the backend object lifetime to the backend
> device (using devm_kzalloc() instead of kzalloc + refcount.
> 
> Basically, we would not need to care about syncing the backend existence with
> accessing it...
> To sum up, the device_links approach tends to be similar (not identical) to the
> previous approach using the component API.
> 
> The biggest pro I see in Bartosz's stuff is flexibility. So it should just work
> in whatever future usecases we might have. I fear that going the device_links
> road we might end up needing this stuff anyways.

I'm keen on it if it simplifies code or becomes the dominant paradigm for such
things in the kernel (so becomes what people expect).  That isn't true yet
and I doubt it will be particularly soon.  If things head that way we can
revisit as it would enable things that currently we don't support - nothing
should break.

Jonathan


> 
> Obviously, the biggest con is code complexity (not that bad though) as we always
> need to properly sync any backend callback.
> 
> - Nuno Sá
> >   
> 

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Nuno Sá]

On Wed, 2024-01-10 at 09:16 +0000, Jonathan Cameron wrote:
> On Tue, 09 Jan 2024 13:15:54 +0100
> Nuno Sá <noname.nuno@gmail.com> wrote:
> 
> > On Tue, 2023-12-26 at 15:59 +0000, Jonathan Cameron wrote:
> > >   
> > > > > > +
> > > > > > +       ret = devm_add_action_or_reset(dev, iio_backend_release,
> > > > > > back);
> > > > > > +       if (ret)
> > > > > > +               return ret;
> > > > > > +
> > > > > > +       link = device_link_add(dev, back->dev,
> > > > > > DL_FLAG_AUTOREMOVE_CONSUMER);
> > > > > > +       if (!link)
> > > > > > +               pr_warn("%s: Could not link to supplier(%s)\n",
> > > > > > dev_name(dev),
> > > > > > +                       dev_name(back->dev));    
> > > > > 
> > > > > Why is that not an error and we try to carry on?    
> > > > 
> > > > I guess having the links are not really mandatory for the whole thing to
> > > > work (more
> > > > like a nice to have). That's also how this is handled in another
> > > > subsystems
> > > > so I
> > > > figured it would be fine.
> > > > 
> > > > But since you are speaking about this... After you pointing me to
> > > > Bartosz's
> > > > talk and
> > > > sawing it (as stuff like this is mentioned), I started to question this.
> > > > The
> > > > goal
> > > > with the above comment is that if you remove the backend, all the
> > > > consumers
> > > > are
> > > > automatically removed (unbound). Just not sure if that's what we always
> > > > want
> > > > (and we
> > > > are already handling the situation where a backend goes away with -
> > > > ENODEV)
> > > > as some
> > > > frontends could still be useful without the backend (I guess that could
> > > > be
> > > > plausible). I think for now we don't really have such usecases so the
> > > > links
> > > > can make
> > > > sense (and we can figure something like optionally creating these links
> > > > if
> > > > we ever
> > > > need too) but having your inputs on this will definitely be valuable.  
> > > 
> > > I'm not keen on both trying to make everything tear down cleanly AND
> > > making
> > > sure
> > > it all works even if we don't. That just adds two code paths to test when
> > > either
> > > should be sufficient on its own.  I don't really mind which.  Bartosz's
> > > stuff  
> > 
> > Agreed...
> > 
> > > is nice, but it may not be the right solution here.   
> > 
> > There's pros and cons on both options... 
> > 
> > For the device links the cons I see is that it depends on patch 3 for it to
> > work
> > (or some other approach if the one in that patch is not good) - not really a
> > real con though :). The biggest concern is (possible) future uses where we
> > end
> > up with cases where removing a backend is not really a "deal breaker". I
> > could
> > think of frontends that have multiple backends (one per data path) and
> > removing
> > one backend would not tear the whole thing down (we would just have one non
> > functional data paths/port where the others are still ok).
> 
> I wouldn't waste time catering to such set ups.  If the whole thing gets
> torn down because one element went away that should be fine.
> To do anything else I'd want to see a real world use case.

Fair enough...

> 
> > 
> > Olivier, for STM usecases, do we always need the backend? I mean, does it
> > make
> > sense to always remove/unbind the frontend in case the backend is unbound?
> > 
> > Maybe some of your usecases already "forces" us with a decision. 
> > 
> > The biggest pro I see is code simplicity. If we can assume the frontend can
> > never exist in case one of the backends is gone, we can:
> > 
> >  * get rid of the sync mutex;
> >  * get rid of the kref and bind the backend object lifetime to the backend
> > device (using devm_kzalloc() instead of kzalloc + refcount.
> > 
> > Basically, we would not need to care about syncing the backend existence
> > with
> > accessing it...
> > To sum up, the device_links approach tends to be similar (not identical) to
> > the
> > previous approach using the component API.
> > 
> > The biggest pro I see in Bartosz's stuff is flexibility. So it should just
> > work
> > in whatever future usecases we might have. I fear that going the
> > device_links
> > road we might end up needing this stuff anyways.
> 
> I'm keen on it if it simplifies code or becomes the dominant paradigm for such
> things in the kernel (so becomes what people expect).  That isn't true yet
> and I doubt it will be particularly soon.  If things head that way we can
> revisit as it would enable things that currently we don't support - nothing
> should break.
> 

Well, If I'm not missing anything, simpler code would be with device_links so I
guess that's your preferred approach for now :). Also fine by me as this is an
in kernel interface so we easily revisit it.

I'll just wait a bit more (before sending v5) to see if Olivier has any
foreseeable usecase where device_links would be an issue.

- Nuno Sá

Re: [PATCH v4 6/8] iio: add the IIO backend framework

[Olivier MOYSAN]

Hi Nuno,

On 1/9/24 13:15, Nuno Sá wrote:
> On Tue, 2023-12-26 at 15:59 +0000, Jonathan Cameron wrote:
>>
>>>>> +
>>>>> +       ret = devm_add_action_or_reset(dev, iio_backend_release, back);
>>>>> +       if (ret)
>>>>> +               return ret;
>>>>> +
>>>>> +       link = device_link_add(dev, back->dev,
>>>>> DL_FLAG_AUTOREMOVE_CONSUMER);
>>>>> +       if (!link)
>>>>> +               pr_warn("%s: Could not link to supplier(%s)\n",
>>>>> dev_name(dev),
>>>>> +                       dev_name(back->dev));
>>>>
>>>> Why is that not an error and we try to carry on?
>>>
>>> I guess having the links are not really mandatory for the whole thing to
>>> work (more
>>> like a nice to have). That's also how this is handled in another subsystems
>>> so I
>>> figured it would be fine.
>>>
>>> But since you are speaking about this... After you pointing me to Bartosz's
>>> talk and
>>> sawing it (as stuff like this is mentioned), I started to question this. The
>>> goal
>>> with the above comment is that if you remove the backend, all the consumers
>>> are
>>> automatically removed (unbound). Just not sure if that's what we always want
>>> (and we
>>> are already handling the situation where a backend goes away with -ENODEV)
>>> as some
>>> frontends could still be useful without the backend (I guess that could be
>>> plausible). I think for now we don't really have such usecases so the links
>>> can make
>>> sense (and we can figure something like optionally creating these links if
>>> we ever
>>> need too) but having your inputs on this will definitely be valuable.
>>
>> I'm not keen on both trying to make everything tear down cleanly AND making
>> sure
>> it all works even if we don't. That just adds two code paths to test when
>> either
>> should be sufficient on its own.  I don't really mind which.  Bartosz's stuff
> 
> Agreed...
> 
>> is nice, but it may not be the right solution here.
> 
> There's pros and cons on both options...
> 
> For the device links the cons I see is that it depends on patch 3 for it to work
> (or some other approach if the one in that patch is not good) - not really a
> real con though :). The biggest concern is (possible) future uses where we end
> up with cases where removing a backend is not really a "deal breaker". I could
> think of frontends that have multiple backends (one per data path) and removing
> one backend would not tear the whole thing down (we would just have one non
> functional data paths/port where the others are still ok).
> 
> Olivier, for STM usecases, do we always need the backend? I mean, does it make
> sense to always remove/unbind the frontend in case the backend is unbound?
> 

In STM usecases we may have severals backends linked to a frontend. But 
I cannot find a usecase where it may be necessary to remove a backend 
while keeping the others alive. So from my side it is acceptable to tear 
everythings down if a backend if removed.

Olivier

> Maybe some of your usecases already "forces" us with a decision.
> 
> The biggest pro I see is code simplicity. If we can assume the frontend can
> never exist in case one of the backends is gone, we can:
> 
>   * get rid of the sync mutex;
>   * get rid of the kref and bind the backend object lifetime to the backend
> device (using devm_kzalloc() instead of kzalloc + refcount.
> 
> Basically, we would not need to care about syncing the backend existence with
> accessing it...
> To sum up, the device_links approach tends to be similar (not identical) to the
> previous approach using the component API.
> 
> The biggest pro I see in Bartosz's stuff is flexibility. So it should just work
> in whatever future usecases we might have. I fear that going the device_links
> road we might end up needing this stuff anyways.
> 
> Obviously, the biggest con is code complexity (not that bad though) as we always
> need to properly sync any backend callback.
> 
> - Nuno Sá
>>