[PATCH v5 0/2] hwmon: (nct6775) Add i2c driver

[PATCH v5 0/2] hwmon: (nct6775) Add i2c driver

[Zev Weiss]

Hello,

This series contains the remaining two outstanding patches adding i2c
support to the nct6775 hwmon driver.

Changes since v4 [0]:
 - Added missing type $ref to nuvoton,tsi-channel-mask property in DT
   binding [Krzysztof, Rob's bot]
 - Added 'F:' line for nuvoton,nct6775.yaml DT binding file to
   MAINTAINERS

The first patch adds a DT binding for the Nuvoton Super I/O chips
supported by the nct6775 driver; the second adds an i2c hwmon driver
wrapped around the new nct6775-core module.

(Since the preparatory work for this that comprised the bulk of the
previous iterations of the series is now in Guenter's hwmon-next tree
this is a somewhat abridged cover letter; see [0] for additional
background info if needed.)

[0] https://lore.kernel.org/linux-hwmon/20220427010154.29749-1-zev@bewilderbeest.net/

Zev Weiss (2):
  dt-bindings: hwmon: Add nuvoton,nct6775
  hwmon: (nct6775) Add i2c driver

 .../bindings/hwmon/nuvoton,nct6775.yaml       |  57 +++++
 MAINTAINERS                                   |   7 +
 drivers/hwmon/Kconfig                         |  17 ++
 drivers/hwmon/Makefile                        |   1 +
 drivers/hwmon/nct6775-i2c.c                   | 195 ++++++++++++++++++
 5 files changed, 277 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
 create mode 100644 drivers/hwmon/nct6775-i2c.c

-- 
2.36.0

[PATCH v5 1/2] dt-bindings: hwmon: Add nuvoton,nct6775

[Zev Weiss]

These Super I/O chips have an i2c interface that some systems expose
to a BMC; the BMC's device tree can now describe that via this
binding.

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
---
 .../bindings/hwmon/nuvoton,nct6775.yaml       | 57 +++++++++++++++++++
 1 file changed, 57 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml

diff --git a/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml b/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
new file mode 100644
index 000000000000..358b262431fc
--- /dev/null
+++ b/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
+%YAML 1.2
+---
+
+$id: http://devicetree.org/schemas/hwmon/nuvoton,nct6775.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: Nuvoton NCT6775 and compatible Super I/O chips
+
+maintainers:
+  - Zev Weiss <zev@bewilderbeest.net>
+
+properties:
+  compatible:
+    enum:
+      - nuvoton,nct6106
+      - nuvoton,nct6116
+      - nuvoton,nct6775
+      - nuvoton,nct6776
+      - nuvoton,nct6779
+      - nuvoton,nct6791
+      - nuvoton,nct6792
+      - nuvoton,nct6793
+      - nuvoton,nct6795
+      - nuvoton,nct6796
+      - nuvoton,nct6797
+      - nuvoton,nct6798
+
+  reg:
+    maxItems: 1
+
+  nuvoton,tsi-channel-mask:
+    description:
+      Bitmask indicating which TSI temperature sensor channels are
+      active.  LSB is TSI0, bit 1 is TSI1, etc.
+    $ref: /schemas/types.yaml#/definitions/uint32
+    maximum: 0xff
+    default: 0
+
+required:
+  - compatible
+  - reg
+
+additionalProperties: false
+
+examples:
+  - |
+    i2c {
+        #address-cells = <1>;
+        #size-cells = <0>;
+
+        superio@4d {
+            compatible = "nuvoton,nct6779";
+            reg = <0x4d>;
+            nuvoton,tsi-channel-mask = <0x03>;
+        };
+    };
-- 
2.36.0

[PATCH v5 2/2] hwmon: (nct6775) Add i2c driver

[Zev Weiss]

This driver provides an i2c I/O mechanism for the core nct6775 driver,
as might be used by a BMC.  Because the Super I/O chip is shared with
the host CPU in such a scenario (and the host should ultimately be in
control of it), the i2c driver is strictly read-only to avoid
interfering with any usage by the host (aside from the bank-select
register, which seems to be replicated for the i2c interface).

Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
Tested-by: Renze Nicolai <renze@rnplus.nl>
---
 MAINTAINERS                 |   7 ++
 drivers/hwmon/Kconfig       |  17 ++++
 drivers/hwmon/Makefile      |   1 +
 drivers/hwmon/nct6775-i2c.c | 195 ++++++++++++++++++++++++++++++++++++
 4 files changed, 220 insertions(+)
 create mode 100644 drivers/hwmon/nct6775-i2c.c

diff --git a/MAINTAINERS b/MAINTAINERS
index 88fdb7cb3197..aac1a184a4c9 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -13538,6 +13538,13 @@ F:	drivers/hwmon/nct6775-core.c
 F:	drivers/hwmon/nct6775-platform.c
 F:	drivers/hwmon/nct6775.h
 
+NCT6775 HARDWARE MONITOR DRIVER - I2C DRIVER
+M:	Zev Weiss <zev@bewilderbeest.net>
+L:	linux-hwmon@vger.kernel.org
+S:	Maintained
+F:	Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
+F:	drivers/hwmon/nct6775-i2c.c
+
 NETDEVSIM
 M:	Jakub Kicinski <kuba@kernel.org>
 S:	Maintained
diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
index 85c22bba439b..a1dac1aa4e3a 100644
--- a/drivers/hwmon/Kconfig
+++ b/drivers/hwmon/Kconfig
@@ -1489,6 +1489,23 @@ config SENSORS_NCT6775
 	  This driver can also be built as a module. If so, the module
 	  will be called nct6775.
 
+config SENSORS_NCT6775_I2C
+	tristate "I2C driver for Nuvoton NCT6775F and compatibles"
+	depends on I2C
+	select REGMAP_I2C
+	select SENSORS_NCT6775
+	help
+	  If you say yes here you get support for the hardware monitoring
+	  functionality of the Nuvoton NCT6106D, NCT6775F, NCT6776F, NCT6779D,
+	  NCT6791D, NCT6792D, NCT6793D, NCT6795D, NCT6796D, and compatible
+	  Super-I/O chips via their I2C interface.
+
+	  If you're not building a kernel for a BMC, this is probably
+	  not the driver you want (see CONFIG_SENSORS_NCT6775_PLATFORM).
+
+	  This driver can also be built as a module. If so, the module
+	  will be called nct6775-i2c.
+
 config SENSORS_NCT7802
 	tristate "Nuvoton NCT7802Y"
 	depends on I2C
diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
index 93f2b774cc5e..004ab87c9b80 100644
--- a/drivers/hwmon/Makefile
+++ b/drivers/hwmon/Makefile
@@ -157,6 +157,7 @@ obj-$(CONFIG_SENSORS_NCT6683)	+= nct6683.o
 obj-$(CONFIG_SENSORS_NCT6775_CORE) += nct6775-core.o
 nct6775-objs			:= nct6775-platform.o
 obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
+obj-$(CONFIG_SENSORS_NCT6775_I2C) += nct6775-i2c.o
 obj-$(CONFIG_SENSORS_NCT7802)	+= nct7802.o
 obj-$(CONFIG_SENSORS_NCT7904)	+= nct7904.o
 obj-$(CONFIG_SENSORS_NPCM7XX)	+= npcm750-pwm-fan.o
diff --git a/drivers/hwmon/nct6775-i2c.c b/drivers/hwmon/nct6775-i2c.c
new file mode 100644
index 000000000000..e1bcd1146191
--- /dev/null
+++ b/drivers/hwmon/nct6775-i2c.c
@@ -0,0 +1,195 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * nct6775-i2c - I2C driver for the hardware monitoring functionality of
+ *	         Nuvoton NCT677x Super-I/O chips
+ *
+ * Copyright (C) 2022 Zev Weiss <zev@bewilderbeest.net>
+ *
+ * This driver interacts with the chip via it's "back door" i2c interface, as
+ * is often exposed to a BMC.  Because the host may still be operating the
+ * chip via the ("front door") LPC interface, this driver cannot assume that
+ * it actually has full control of the chip, and in particular must avoid
+ * making any changes that could confuse the host's LPC usage of it.  It thus
+ * operates in a strictly read-only fashion, with the only exception being the
+ * bank-select register (which seems, thankfully, to be replicated for the i2c
+ * interface so it doesn't affect the LPC interface).
+ */
+
+#include <linux/module.h>
+#include <linux/init.h>
+#include <linux/i2c.h>
+#include <linux/hwmon.h>
+#include <linux/hwmon-sysfs.h>
+#include <linux/err.h>
+#include <linux/of_device.h>
+#include <linux/regmap.h>
+#include "nct6775.h"
+
+static int nct6775_i2c_read(void *ctx, unsigned int reg, unsigned int *val)
+{
+	int ret;
+	u32 tmp;
+	u8 bank = reg >> 8;
+	struct nct6775_data *data = ctx;
+	struct i2c_client *client = data->driver_data;
+
+	if (bank != data->bank) {
+		ret = i2c_smbus_write_byte_data(client, NCT6775_REG_BANK, bank);
+		if (ret)
+			return ret;
+		data->bank = bank;
+	}
+
+	ret = i2c_smbus_read_byte_data(client, reg & 0xff);
+	if (ret < 0)
+		return ret;
+	tmp = ret;
+
+	if (nct6775_reg_is_word_sized(data, reg)) {
+		ret = i2c_smbus_read_byte_data(client, (reg & 0xff) + 1);
+		if (ret < 0)
+			return ret;
+		tmp = (tmp << 8) | ret;
+	}
+
+	*val = tmp;
+	return 0;
+}
+
+/*
+ * The write operation is a dummy so as not to disturb anything being done
+ * with the chip via LPC.
+ */
+static int nct6775_i2c_write(void *ctx, unsigned int reg, unsigned int value)
+{
+	struct nct6775_data *data = ctx;
+	struct i2c_client *client = data->driver_data;
+
+	dev_dbg(&client->dev, "skipping attempted write: %02x -> %03x\n", value, reg);
+
+	/*
+	 * This is a lie, but writing anything but the bank-select register is
+	 * something this driver shouldn't be doing.
+	 */
+	return 0;
+}
+
+static const struct of_device_id __maybe_unused nct6775_i2c_of_match[] = {
+	{ .compatible = "nuvoton,nct6106", .data = (void *)nct6106, },
+	{ .compatible = "nuvoton,nct6116", .data = (void *)nct6116, },
+	{ .compatible = "nuvoton,nct6775", .data = (void *)nct6775, },
+	{ .compatible = "nuvoton,nct6776", .data = (void *)nct6776, },
+	{ .compatible = "nuvoton,nct6779", .data = (void *)nct6779, },
+	{ .compatible = "nuvoton,nct6791", .data = (void *)nct6791, },
+	{ .compatible = "nuvoton,nct6792", .data = (void *)nct6792, },
+	{ .compatible = "nuvoton,nct6793", .data = (void *)nct6793, },
+	{ .compatible = "nuvoton,nct6795", .data = (void *)nct6795, },
+	{ .compatible = "nuvoton,nct6796", .data = (void *)nct6796, },
+	{ .compatible = "nuvoton,nct6797", .data = (void *)nct6797, },
+	{ .compatible = "nuvoton,nct6798", .data = (void *)nct6798, },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, nct6775_i2c_of_match);
+
+static const struct i2c_device_id nct6775_i2c_id[] = {
+	{ "nct6106", nct6106 },
+	{ "nct6116", nct6116 },
+	{ "nct6775", nct6775 },
+	{ "nct6776", nct6776 },
+	{ "nct6779", nct6779 },
+	{ "nct6791", nct6791 },
+	{ "nct6792", nct6792 },
+	{ "nct6793", nct6793 },
+	{ "nct6795", nct6795 },
+	{ "nct6796", nct6796 },
+	{ "nct6797", nct6797 },
+	{ "nct6798", nct6798 },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, nct6775_i2c_id);
+
+static int nct6775_i2c_probe_init(struct nct6775_data *data)
+{
+	u32 tsi_channel_mask;
+	struct i2c_client *client = data->driver_data;
+
+	/*
+	 * The i2c interface doesn't provide access to the control registers
+	 * needed to determine the presence of other fans, but fans 1 and 2
+	 * are (in principle) always there.
+	 *
+	 * In practice this is perhaps a little silly, because the system
+	 * using this driver is mostly likely a BMC, and hence probably has
+	 * totally separate fan tachs & pwms of its own that are actually
+	 * controlling/monitoring the fans -- these are thus unlikely to be
+	 * doing anything actually useful.
+	 */
+	data->has_fan = 0x03;
+	data->has_fan_min = 0x03;
+	data->has_pwm = 0x03;
+
+	/*
+	 * Because on a BMC this driver may be bound very shortly after power
+	 * is first applied to the device, the automatic TSI channel detection
+	 * in nct6775_probe() (which has already been run at this point) may
+	 * not find anything if a channel hasn't yet produced a temperature
+	 * reading.  Augment whatever was found via autodetection (if
+	 * anything) with the channels DT says should be active.
+	 */
+	if (!of_property_read_u32(client->dev.of_node, "nuvoton,tsi-channel-mask",
+				  &tsi_channel_mask))
+		data->have_tsi_temp |= tsi_channel_mask & GENMASK(NUM_TSI_TEMP - 1, 0);
+
+	return 0;
+}
+
+static const struct regmap_config nct6775_i2c_regmap_config = {
+	.reg_bits = 16,
+	.val_bits = 16,
+	.reg_read = nct6775_i2c_read,
+	.reg_write = nct6775_i2c_write,
+};
+
+static int nct6775_i2c_probe(struct i2c_client *client)
+{
+	struct nct6775_data *data;
+	const struct of_device_id *of_id;
+	const struct i2c_device_id *i2c_id;
+	struct device *dev = &client->dev;
+
+	of_id = of_match_device(nct6775_i2c_of_match, dev);
+	i2c_id = i2c_match_id(nct6775_i2c_id, client);
+
+	if (of_id && (unsigned long)of_id->data != i2c_id->driver_data)
+		dev_notice(dev, "Device mismatch: %s in device tree, %s detected\n",
+			   of_id->name, i2c_id->name);
+
+	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->kind = i2c_id->driver_data;
+
+	data->read_only = true;
+	data->driver_data = client;
+	data->driver_init = nct6775_i2c_probe_init;
+
+	return nct6775_probe(dev, data, &nct6775_i2c_regmap_config);
+}
+
+static struct i2c_driver nct6775_i2c_driver = {
+	.class = I2C_CLASS_HWMON,
+	.driver = {
+		.name = "nct6775-i2c",
+		.of_match_table = of_match_ptr(nct6775_i2c_of_match),
+	},
+	.probe_new = nct6775_i2c_probe,
+	.id_table = nct6775_i2c_id,
+};
+
+module_i2c_driver(nct6775_i2c_driver);
+
+MODULE_AUTHOR("Zev Weiss <zev@bewilderbeest.net>");
+MODULE_DESCRIPTION("I2C driver for NCT6775F and compatible chips");
+MODULE_LICENSE("GPL");
+MODULE_IMPORT_NS(HWMON_NCT6775);
-- 
2.36.0

Re: [PATCH v5 1/2] dt-bindings: hwmon: Add nuvoton,nct6775

[Rob Herring]

On Wed, 27 Apr 2022 18:27:06 -0700, Zev Weiss wrote:
> These Super I/O chips have an i2c interface that some systems expose
> to a BMC; the BMC's device tree can now describe that via this
> binding.
> 
> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
> ---
>  .../bindings/hwmon/nuvoton,nct6775.yaml       | 57 +++++++++++++++++++
>  1 file changed, 57 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
> 

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

Re: [PATCH v5 1/2] dt-bindings: hwmon: Add nuvoton,nct6775

[Guenter Roeck]

On Wed, Apr 27, 2022 at 06:27:06PM -0700, Zev Weiss wrote:
> These Super I/O chips have an i2c interface that some systems expose
> to a BMC; the BMC's device tree can now describe that via this
> binding.
> 
> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
> Reviewed-by: Rob Herring <robh@kernel.org>

Applied.

Thanks,
Guenter

> ---
>  .../bindings/hwmon/nuvoton,nct6775.yaml       | 57 +++++++++++++++++++
>  1 file changed, 57 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
> 
> diff --git a/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml b/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
> new file mode 100644
> index 000000000000..358b262431fc
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
> @@ -0,0 +1,57 @@
> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
> +%YAML 1.2
> +---
> +
> +$id: http://devicetree.org/schemas/hwmon/nuvoton,nct6775.yaml#
> +$schema: http://devicetree.org/meta-schemas/core.yaml#
> +
> +title: Nuvoton NCT6775 and compatible Super I/O chips
> +
> +maintainers:
> +  - Zev Weiss <zev@bewilderbeest.net>
> +
> +properties:
> +  compatible:
> +    enum:
> +      - nuvoton,nct6106
> +      - nuvoton,nct6116
> +      - nuvoton,nct6775
> +      - nuvoton,nct6776
> +      - nuvoton,nct6779
> +      - nuvoton,nct6791
> +      - nuvoton,nct6792
> +      - nuvoton,nct6793
> +      - nuvoton,nct6795
> +      - nuvoton,nct6796
> +      - nuvoton,nct6797
> +      - nuvoton,nct6798
> +
> +  reg:
> +    maxItems: 1
> +
> +  nuvoton,tsi-channel-mask:
> +    description:
> +      Bitmask indicating which TSI temperature sensor channels are
> +      active.  LSB is TSI0, bit 1 is TSI1, etc.
> +    $ref: /schemas/types.yaml#/definitions/uint32
> +    maximum: 0xff
> +    default: 0
> +
> +required:
> +  - compatible
> +  - reg
> +
> +additionalProperties: false
> +
> +examples:
> +  - |
> +    i2c {
> +        #address-cells = <1>;
> +        #size-cells = <0>;
> +
> +        superio@4d {
> +            compatible = "nuvoton,nct6779";
> +            reg = <0x4d>;
> +            nuvoton,tsi-channel-mask = <0x03>;
> +        };
> +    };

Re: [PATCH v5 2/2] hwmon: (nct6775) Add i2c driver

[Guenter Roeck]

On Wed, Apr 27, 2022 at 06:27:07PM -0700, Zev Weiss wrote:
> This driver provides an i2c I/O mechanism for the core nct6775 driver,
> as might be used by a BMC.  Because the Super I/O chip is shared with
> the host CPU in such a scenario (and the host should ultimately be in
> control of it), the i2c driver is strictly read-only to avoid
> interfering with any usage by the host (aside from the bank-select
> register, which seems to be replicated for the i2c interface).
> 
> Signed-off-by: Zev Weiss <zev@bewilderbeest.net>
> Tested-by: Renze Nicolai <renze@rnplus.nl>

Applied.

Thanks,
Guenter

> ---
>  MAINTAINERS                 |   7 ++
>  drivers/hwmon/Kconfig       |  17 ++++
>  drivers/hwmon/Makefile      |   1 +
>  drivers/hwmon/nct6775-i2c.c | 195 ++++++++++++++++++++++++++++++++++++
>  4 files changed, 220 insertions(+)
>  create mode 100644 drivers/hwmon/nct6775-i2c.c
> 
> diff --git a/MAINTAINERS b/MAINTAINERS
> index 88fdb7cb3197..aac1a184a4c9 100644
> --- a/MAINTAINERS
> +++ b/MAINTAINERS
> @@ -13538,6 +13538,13 @@ F:	drivers/hwmon/nct6775-core.c
>  F:	drivers/hwmon/nct6775-platform.c
>  F:	drivers/hwmon/nct6775.h
>  
> +NCT6775 HARDWARE MONITOR DRIVER - I2C DRIVER
> +M:	Zev Weiss <zev@bewilderbeest.net>
> +L:	linux-hwmon@vger.kernel.org
> +S:	Maintained
> +F:	Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
> +F:	drivers/hwmon/nct6775-i2c.c
> +
>  NETDEVSIM
>  M:	Jakub Kicinski <kuba@kernel.org>
>  S:	Maintained
> diff --git a/drivers/hwmon/Kconfig b/drivers/hwmon/Kconfig
> index 85c22bba439b..a1dac1aa4e3a 100644
> --- a/drivers/hwmon/Kconfig
> +++ b/drivers/hwmon/Kconfig
> @@ -1489,6 +1489,23 @@ config SENSORS_NCT6775
>  	  This driver can also be built as a module. If so, the module
>  	  will be called nct6775.
>  
> +config SENSORS_NCT6775_I2C
> +	tristate "I2C driver for Nuvoton NCT6775F and compatibles"
> +	depends on I2C
> +	select REGMAP_I2C
> +	select SENSORS_NCT6775
> +	help
> +	  If you say yes here you get support for the hardware monitoring
> +	  functionality of the Nuvoton NCT6106D, NCT6775F, NCT6776F, NCT6779D,
> +	  NCT6791D, NCT6792D, NCT6793D, NCT6795D, NCT6796D, and compatible
> +	  Super-I/O chips via their I2C interface.
> +
> +	  If you're not building a kernel for a BMC, this is probably
> +	  not the driver you want (see CONFIG_SENSORS_NCT6775_PLATFORM).
> +
> +	  This driver can also be built as a module. If so, the module
> +	  will be called nct6775-i2c.
> +
>  config SENSORS_NCT7802
>  	tristate "Nuvoton NCT7802Y"
>  	depends on I2C
> diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> index 93f2b774cc5e..004ab87c9b80 100644
> --- a/drivers/hwmon/Makefile
> +++ b/drivers/hwmon/Makefile
> @@ -157,6 +157,7 @@ obj-$(CONFIG_SENSORS_NCT6683)	+= nct6683.o
>  obj-$(CONFIG_SENSORS_NCT6775_CORE) += nct6775-core.o
>  nct6775-objs			:= nct6775-platform.o
>  obj-$(CONFIG_SENSORS_NCT6775)	+= nct6775.o
> +obj-$(CONFIG_SENSORS_NCT6775_I2C) += nct6775-i2c.o
>  obj-$(CONFIG_SENSORS_NCT7802)	+= nct7802.o
>  obj-$(CONFIG_SENSORS_NCT7904)	+= nct7904.o
>  obj-$(CONFIG_SENSORS_NPCM7XX)	+= npcm750-pwm-fan.o
> diff --git a/drivers/hwmon/nct6775-i2c.c b/drivers/hwmon/nct6775-i2c.c
> new file mode 100644
> index 000000000000..e1bcd1146191
> --- /dev/null
> +++ b/drivers/hwmon/nct6775-i2c.c
> @@ -0,0 +1,195 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * nct6775-i2c - I2C driver for the hardware monitoring functionality of
> + *	         Nuvoton NCT677x Super-I/O chips
> + *
> + * Copyright (C) 2022 Zev Weiss <zev@bewilderbeest.net>
> + *
> + * This driver interacts with the chip via it's "back door" i2c interface, as
> + * is often exposed to a BMC.  Because the host may still be operating the
> + * chip via the ("front door") LPC interface, this driver cannot assume that
> + * it actually has full control of the chip, and in particular must avoid
> + * making any changes that could confuse the host's LPC usage of it.  It thus
> + * operates in a strictly read-only fashion, with the only exception being the
> + * bank-select register (which seems, thankfully, to be replicated for the i2c
> + * interface so it doesn't affect the LPC interface).
> + */
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/i2c.h>
> +#include <linux/hwmon.h>
> +#include <linux/hwmon-sysfs.h>
> +#include <linux/err.h>
> +#include <linux/of_device.h>
> +#include <linux/regmap.h>
> +#include "nct6775.h"
> +
> +static int nct6775_i2c_read(void *ctx, unsigned int reg, unsigned int *val)
> +{
> +	int ret;
> +	u32 tmp;
> +	u8 bank = reg >> 8;
> +	struct nct6775_data *data = ctx;
> +	struct i2c_client *client = data->driver_data;
> +
> +	if (bank != data->bank) {
> +		ret = i2c_smbus_write_byte_data(client, NCT6775_REG_BANK, bank);
> +		if (ret)
> +			return ret;
> +		data->bank = bank;
> +	}
> +
> +	ret = i2c_smbus_read_byte_data(client, reg & 0xff);
> +	if (ret < 0)
> +		return ret;
> +	tmp = ret;
> +
> +	if (nct6775_reg_is_word_sized(data, reg)) {
> +		ret = i2c_smbus_read_byte_data(client, (reg & 0xff) + 1);
> +		if (ret < 0)
> +			return ret;
> +		tmp = (tmp << 8) | ret;
> +	}
> +
> +	*val = tmp;
> +	return 0;
> +}
> +
> +/*
> + * The write operation is a dummy so as not to disturb anything being done
> + * with the chip via LPC.
> + */
> +static int nct6775_i2c_write(void *ctx, unsigned int reg, unsigned int value)
> +{
> +	struct nct6775_data *data = ctx;
> +	struct i2c_client *client = data->driver_data;
> +
> +	dev_dbg(&client->dev, "skipping attempted write: %02x -> %03x\n", value, reg);
> +
> +	/*
> +	 * This is a lie, but writing anything but the bank-select register is
> +	 * something this driver shouldn't be doing.
> +	 */
> +	return 0;
> +}
> +
> +static const struct of_device_id __maybe_unused nct6775_i2c_of_match[] = {
> +	{ .compatible = "nuvoton,nct6106", .data = (void *)nct6106, },
> +	{ .compatible = "nuvoton,nct6116", .data = (void *)nct6116, },
> +	{ .compatible = "nuvoton,nct6775", .data = (void *)nct6775, },
> +	{ .compatible = "nuvoton,nct6776", .data = (void *)nct6776, },
> +	{ .compatible = "nuvoton,nct6779", .data = (void *)nct6779, },
> +	{ .compatible = "nuvoton,nct6791", .data = (void *)nct6791, },
> +	{ .compatible = "nuvoton,nct6792", .data = (void *)nct6792, },
> +	{ .compatible = "nuvoton,nct6793", .data = (void *)nct6793, },
> +	{ .compatible = "nuvoton,nct6795", .data = (void *)nct6795, },
> +	{ .compatible = "nuvoton,nct6796", .data = (void *)nct6796, },
> +	{ .compatible = "nuvoton,nct6797", .data = (void *)nct6797, },
> +	{ .compatible = "nuvoton,nct6798", .data = (void *)nct6798, },
> +	{ },
> +};
> +MODULE_DEVICE_TABLE(of, nct6775_i2c_of_match);
> +
> +static const struct i2c_device_id nct6775_i2c_id[] = {
> +	{ "nct6106", nct6106 },
> +	{ "nct6116", nct6116 },
> +	{ "nct6775", nct6775 },
> +	{ "nct6776", nct6776 },
> +	{ "nct6779", nct6779 },
> +	{ "nct6791", nct6791 },
> +	{ "nct6792", nct6792 },
> +	{ "nct6793", nct6793 },
> +	{ "nct6795", nct6795 },
> +	{ "nct6796", nct6796 },
> +	{ "nct6797", nct6797 },
> +	{ "nct6798", nct6798 },
> +	{ }
> +};
> +MODULE_DEVICE_TABLE(i2c, nct6775_i2c_id);
> +
> +static int nct6775_i2c_probe_init(struct nct6775_data *data)
> +{
> +	u32 tsi_channel_mask;
> +	struct i2c_client *client = data->driver_data;
> +
> +	/*
> +	 * The i2c interface doesn't provide access to the control registers
> +	 * needed to determine the presence of other fans, but fans 1 and 2
> +	 * are (in principle) always there.
> +	 *
> +	 * In practice this is perhaps a little silly, because the system
> +	 * using this driver is mostly likely a BMC, and hence probably has
> +	 * totally separate fan tachs & pwms of its own that are actually
> +	 * controlling/monitoring the fans -- these are thus unlikely to be
> +	 * doing anything actually useful.
> +	 */
> +	data->has_fan = 0x03;
> +	data->has_fan_min = 0x03;
> +	data->has_pwm = 0x03;
> +
> +	/*
> +	 * Because on a BMC this driver may be bound very shortly after power
> +	 * is first applied to the device, the automatic TSI channel detection
> +	 * in nct6775_probe() (which has already been run at this point) may
> +	 * not find anything if a channel hasn't yet produced a temperature
> +	 * reading.  Augment whatever was found via autodetection (if
> +	 * anything) with the channels DT says should be active.
> +	 */
> +	if (!of_property_read_u32(client->dev.of_node, "nuvoton,tsi-channel-mask",
> +				  &tsi_channel_mask))
> +		data->have_tsi_temp |= tsi_channel_mask & GENMASK(NUM_TSI_TEMP - 1, 0);
> +
> +	return 0;
> +}
> +
> +static const struct regmap_config nct6775_i2c_regmap_config = {
> +	.reg_bits = 16,
> +	.val_bits = 16,
> +	.reg_read = nct6775_i2c_read,
> +	.reg_write = nct6775_i2c_write,
> +};
> +
> +static int nct6775_i2c_probe(struct i2c_client *client)
> +{
> +	struct nct6775_data *data;
> +	const struct of_device_id *of_id;
> +	const struct i2c_device_id *i2c_id;
> +	struct device *dev = &client->dev;
> +
> +	of_id = of_match_device(nct6775_i2c_of_match, dev);
> +	i2c_id = i2c_match_id(nct6775_i2c_id, client);
> +
> +	if (of_id && (unsigned long)of_id->data != i2c_id->driver_data)
> +		dev_notice(dev, "Device mismatch: %s in device tree, %s detected\n",
> +			   of_id->name, i2c_id->name);
> +
> +	data = devm_kzalloc(&client->dev, sizeof(*data), GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	data->kind = i2c_id->driver_data;
> +
> +	data->read_only = true;
> +	data->driver_data = client;
> +	data->driver_init = nct6775_i2c_probe_init;
> +
> +	return nct6775_probe(dev, data, &nct6775_i2c_regmap_config);
> +}
> +
> +static struct i2c_driver nct6775_i2c_driver = {
> +	.class = I2C_CLASS_HWMON,
> +	.driver = {
> +		.name = "nct6775-i2c",
> +		.of_match_table = of_match_ptr(nct6775_i2c_of_match),
> +	},
> +	.probe_new = nct6775_i2c_probe,
> +	.id_table = nct6775_i2c_id,
> +};
> +
> +module_i2c_driver(nct6775_i2c_driver);
> +
> +MODULE_AUTHOR("Zev Weiss <zev@bewilderbeest.net>");
> +MODULE_DESCRIPTION("I2C driver for NCT6775F and compatible chips");
> +MODULE_LICENSE("GPL");
> +MODULE_IMPORT_NS(HWMON_NCT6775);