[PATCH 0/3] Add bridged amplifiers to cs42l43

[PATCH 0/3] Add bridged amplifiers to cs42l43

[Charles Keepax]

On some cs42l43 systems a couple of cs35l56 amplifiers are attached
to the cs42l43's SPI and I2S. On Windows the cs42l43 is controlled
by a SDCA class driver and these two amplifiers are controlled by
firmware running on the cs42l43. However, under Linux the decision
was made to interact with the cs42l43 directly, affording the user
greater control over the audio system. However, this has resulted
in an issue where these two bridged cs35l56 amplifiers are not
populated in ACPI and must be added manually. There is at least an
SDCA extension unit DT entry we can key off.

The process of adding this is handled using a software node, firstly the
ability to add native chip selects to software nodes must be added.
Secondly, an additional flag for naming the SPI devices is added this
allows the machine driver to key to the correct amplifier. Then finally,
the cs42l43 SPI driver adds the two amplifiers directly onto its SPI
bus.

An additional series will follow soon to add the audio machine driver
parts (in the sof-sdw driver), however that is fairly orthogonal to
this part of the process, getting the actual amplifiers registered.

Thanks,
Charles

Charles Keepax (2):
  gpio: swnode: Add ability to specify native chip selects for SPI
  spi: Add a mechanism to use the fwnode name for the SPI device

Maciej Strozek (1):
  spi: cs42l43: Add bridged cs35l56 amplifiers

 drivers/gpio/gpiolib-swnode.c |   8 ++
 drivers/gpio/gpiolib.c        |   9 ++
 drivers/spi/spi-cs42l43.c     | 152 +++++++++++++++++++++++++++++++++-
 drivers/spi/spi.c             |   7 ++
 include/linux/gpio/consumer.h |   4 +
 include/linux/spi/spi.h       |   2 +
 6 files changed, 181 insertions(+), 1 deletion(-)

-- 
2.39.2

[PATCH 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Charles Keepax]

SPI devices can specify a cs-gpios property to enumerate their
chip selects. Under device tree, a zero entry in this property can
be used to specify that a particular chip select is using the SPI
controllers native chip select, for example:

        cs-gpios = <&gpio1 0 0>, <0>;

Here the second chip select is native. However, when using swnodes
there is currently no way to specify a native chip select. The
proposal here is to register a swnode_gpio_undefined software node,
that can be specified to allow the indication of a native chip
select. For example:

static const struct software_node_ref_args device_cs_refs[] = {
	{
		.node  = &device_gpiochip_swnode,
		.nargs = 2,
		.args  = { 0, GPIO_ACTIVE_LOW },
	},
	{
		.node  = &swnode_gpio_undefined,
		.nargs = 0,
	},
};

Register the swnode as the gpiolib is initialised and
check in swnode_get_gpio_device if the returned node matches
swnode_gpio_undefined and return -ENOENT, which matches the behaviour
of the device tree system when it encounters a 0 phandle.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/gpio/gpiolib-swnode.c | 8 ++++++++
 drivers/gpio/gpiolib.c        | 9 +++++++++
 include/linux/gpio/consumer.h | 4 ++++
 3 files changed, 21 insertions(+)

diff --git a/drivers/gpio/gpiolib-swnode.c b/drivers/gpio/gpiolib-swnode.c
index fa52bdb1a29a..801b5a660307 100644
--- a/drivers/gpio/gpiolib-swnode.c
+++ b/drivers/gpio/gpiolib-swnode.c
@@ -17,6 +17,11 @@
 #include "gpiolib.h"
 #include "gpiolib-swnode.h"
 
+const struct software_node swnode_gpio_undefined = {
+	.name = "gpio-internal-undefined",
+};
+EXPORT_SYMBOL_GPL(swnode_gpio_undefined);
+
 static void swnode_format_propname(const char *con_id, char *propname,
 				   size_t max_size)
 {
@@ -40,6 +45,9 @@ static struct gpio_device *swnode_get_gpio_device(struct fwnode_handle *fwnode)
 	if (!gdev_node || !gdev_node->name)
 		return ERR_PTR(-EINVAL);
 
+	if (!strcmp(gdev_node->name, "gpio-internal-undefined"))
+		return ERR_PTR(-ENOENT);
+
 	gdev = gpio_device_find_by_label(gdev_node->name);
 	return gdev ?: ERR_PTR(-EPROBE_DEFER);
 }
diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index ce94e37bcbee..e3a7e2a3a323 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4892,8 +4892,17 @@ DEFINE_SEQ_ATTRIBUTE(gpiolib);
 
 static int __init gpiolib_debugfs_init(void)
 {
+	int ret;
+
+	ret = software_node_register(&swnode_gpio_undefined);
+	if (ret < 0) {
+		pr_err("gpiolib: failed to register swnode: %d\n", ret);
+		return ret;
+	}
+
 	/* /sys/kernel/debug/gpio */
 	debugfs_create_file("gpio", 0444, NULL, NULL, &gpiolib_fops);
+
 	return 0;
 }
 subsys_initcall(gpiolib_debugfs_init);
diff --git a/include/linux/gpio/consumer.h b/include/linux/gpio/consumer.h
index db2dfbae8edb..e685fac43398 100644
--- a/include/linux/gpio/consumer.h
+++ b/include/linux/gpio/consumer.h
@@ -12,6 +12,8 @@ struct fwnode_handle;
 struct gpio_array;
 struct gpio_desc;
 
+struct software_node;
+
 /**
  * struct gpio_descs - Struct containing an array of descriptors that can be
  *                     obtained using gpiod_get_array()
@@ -54,6 +56,8 @@ enum gpiod_flags {
 	GPIOD_OUT_HIGH_OPEN_DRAIN = GPIOD_OUT_HIGH | GPIOD_FLAGS_BIT_OPEN_DRAIN,
 };
 
+extern const struct software_node swnode_gpio_undefined;
+
 #ifdef CONFIG_GPIOLIB
 
 /* Return the number of GPIOs associated with a device / function */
-- 
2.39.2

[PATCH 2/3] spi: Add a mechanism to use the fwnode name for the SPI device

[Charles Keepax]

Add a mechanism to force the use of the fwnode name for the name of the
SPI device itself. This is useful when devices need to be manually added
within the kernel.

Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/spi/spi.c       | 7 +++++++
 include/linux/spi/spi.h | 2 ++
 2 files changed, 9 insertions(+)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index ff75838c1b5d..fae0787beece 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -598,6 +598,12 @@ EXPORT_SYMBOL_GPL(spi_alloc_device);
 static void spi_dev_set_name(struct spi_device *spi)
 {
 	struct acpi_device *adev = ACPI_COMPANION(&spi->dev);
+	struct fwnode_handle *fwnode = dev_fwnode(&spi->dev);
+
+	if (spi->use_fwnode_name && fwnode) {
+		dev_set_name(&spi->dev, "spi-%s", fwnode_get_name(fwnode));
+		return;
+	}
 
 	if (adev) {
 		dev_set_name(&spi->dev, "spi-%s", acpi_dev_name(adev));
@@ -830,6 +836,7 @@ struct spi_device *spi_new_device(struct spi_controller *ctlr,
 	 * spi->cs_index_mask as 0x01.
 	 */
 	proxy->cs_index_mask = 0x01;
+	proxy->use_fwnode_name = chip->use_fwnode_name;
 
 	if (chip->swnode) {
 		status = device_add_software_node(&proxy->dev, chip->swnode);
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index c459809efee4..25461775718d 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -222,6 +222,7 @@ struct spi_device {
 	struct spi_delay	cs_setup;
 	struct spi_delay	cs_hold;
 	struct spi_delay	cs_inactive;
+	bool			use_fwnode_name;
 
 	/* The statistics */
 	struct spi_statistics __percpu	*pcpu_statistics;
@@ -1608,6 +1609,7 @@ struct spi_board_info {
 	char		modalias[SPI_NAME_SIZE];
 	const void	*platform_data;
 	const struct software_node *swnode;
+	bool		use_fwnode_name;
 	void		*controller_data;
 	int		irq;
 
-- 
2.39.2

[PATCH 3/3] spi: cs42l43: Add bridged cs35l56 amplifiers

[Charles Keepax]

From: Maciej Strozek <mstrozek@opensource.cirrus.com>

On some cs42l43 systems a couple of cs35l56 amplifiers are attached
to the cs42l43's SPI and I2S. On Windows the cs42l43 is controlled
by a SDCA class driver and these two amplifiers are controlled by
firmware running on the cs42l43. However, under Linux the decision
was made to interact with the cs42l43 directly, affording the user
greater control over the audio system. However, this has resulted
in an issue where these two bridged cs35l56 amplifiers are not
populated in ACPI and must be added manually.

Check for the presence of the "01fa-cirrus-sidecar-instances" property
in the SDCA extension unit's ACPI properties to confirm the presence
of these two amplifiers and if they exist add them manually onto the
SPI bus.

Signed-off-by: Maciej Strozek <mstrozek@opensource.cirrus.com>
Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>
---
 drivers/spi/spi-cs42l43.c | 152 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 151 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-cs42l43.c b/drivers/spi/spi-cs42l43.c
index aabef9fc84bd..3620d4059034 100644
--- a/drivers/spi/spi-cs42l43.c
+++ b/drivers/spi/spi-cs42l43.c
@@ -5,6 +5,8 @@
 // Copyright (C) 2022-2023 Cirrus Logic, Inc. and
 //                         Cirrus Logic International Semiconductor Ltd.
 
+#include <dt-bindings/gpio/gpio.h>
+#include <linux/acpi.h>
 #include <linux/bits.h>
 #include <linux/bitfield.h>
 #include <linux/device.h>
@@ -39,6 +41,59 @@ static const unsigned int cs42l43_clock_divs[] = {
 	2, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30
 };
 
+const struct software_node ampl = {
+	.name			= "cs35l56-left",
+};
+
+const struct software_node ampr = {
+	.name			= "cs35l56-right",
+};
+
+struct spi_board_info ampl_info = {
+	.modalias		= "cs35l56",
+	.max_speed_hz		= 2000000,
+	.chip_select		= 0,
+	.mode			= SPI_MODE_0,
+	.swnode			= &ampl,
+	.use_fwnode_name	= true,
+};
+
+struct spi_board_info ampr_info = {
+	.modalias		= "cs35l56",
+	.max_speed_hz		= 2000000,
+	.chip_select		= 1,
+	.mode			= SPI_MODE_0,
+	.swnode			= &ampr,
+	.use_fwnode_name	= true,
+};
+
+static const struct software_node cs42l43_gpiochip_swnode = {
+	.name			= "cs42l43-pinctrl",
+};
+
+static const struct software_node_ref_args cs42l43_cs_refs[] = {
+	{
+		.node		= &cs42l43_gpiochip_swnode,
+		.nargs		= 2,
+		.args		= { 0, GPIO_ACTIVE_LOW },
+	},
+	{
+		.node		= &swnode_gpio_undefined,
+		.nargs		= 0,
+	},
+};
+
+static const struct property_entry cs42l43_cs_props[] = {
+	{
+		.name		= "cs-gpios",
+		.length		= ARRAY_SIZE(cs42l43_cs_refs) *
+				  sizeof(struct software_node_ref_args),
+		.type		= DEV_PROP_REF,
+		.pointer	= cs42l43_cs_refs,
+	},
+	{}
+};
+
 static int cs42l43_spi_tx(struct regmap *regmap, const u8 *buf, unsigned int len)
 {
 	const u8 *end = buf + len;
@@ -203,6 +258,51 @@ static size_t cs42l43_spi_max_length(struct spi_device *spi)
 	return CS42L43_SPI_MAX_LENGTH;
 }
 
+#if IS_ENABLED(CONFIG_ACPI)
+static bool cs42l43_has_sidecar(struct fwnode_handle *fwnode)
+{
+	static const int func_smart_amp = 0x1;
+	struct fwnode_handle *child_fwnode, *ext_fwnode;
+	unsigned long long function;
+	unsigned int val;
+	int ret;
+
+	if (!is_acpi_node(fwnode))
+		return false;
+
+	fwnode_for_each_child_node(fwnode, child_fwnode) {
+		struct acpi_device *adev = to_acpi_device_node(child_fwnode);
+
+		ret = acpi_evaluate_integer(adev->handle, "_ADR", NULL, &function);
+		if (ACPI_FAILURE(ret))
+			continue;
+
+		if (function != func_smart_amp)
+			continue;
+
+		ext_fwnode = fwnode_get_named_child_node(child_fwnode,
+				"mipi-sdca-function-expansion-subproperties");
+		if (!ext_fwnode)
+			continue;
+
+		ret = fwnode_property_read_u32(ext_fwnode,
+					       "01fa-cirrus-sidecar-instances",
+					       &val);
+		if (ret)
+			continue;
+
+		return !!val;
+	}
+
+	return false;
+}
+#else
+static bool cs42l43_has_sidecar(struct fwnode_handle *fwnode)
+{
+	return false;
+}
+#endif
+
 static void cs42l43_release_of_node(void *data)
 {
 	fwnode_handle_put(data);
@@ -213,6 +313,7 @@ static int cs42l43_spi_probe(struct platform_device *pdev)
 	struct cs42l43 *cs42l43 = dev_get_drvdata(pdev->dev.parent);
 	struct cs42l43_spi *priv;
 	struct fwnode_handle *fwnode = dev_fwnode(cs42l43->dev);
+	bool has_sidecar = cs42l43_has_sidecar(fwnode);
 	int ret;
 
 	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
@@ -266,16 +367,64 @@ static int cs42l43_spi_probe(struct platform_device *pdev)
 		}
 	}
 
-	device_set_node(&priv->ctlr->dev, fwnode);
+	if (has_sidecar) {
+		ret = software_node_register(&cs42l43_gpiochip_swnode);
+		if (ret) {
+			dev_err(priv->dev, "Failed to register gpio swnode: %d\n", ret);
+			return ret;
+		}
+
+		ret = device_create_managed_software_node(&priv->ctlr->dev, cs42l43_cs_props, NULL);
+		if (ret) {
+			dev_err(priv->dev, "Failed to add swnode: %d\n", ret);
+			goto err;
+		}
+
+	} else {
+		device_set_node(&priv->ctlr->dev, fwnode);
+	}
 
 	ret = devm_spi_register_controller(priv->dev, priv->ctlr);
 	if (ret) {
 		dev_err(priv->dev, "Failed to register SPI controller: %d\n", ret);
+		goto err;
 	}
 
+	if (has_sidecar) {
+		if (!spi_new_device(priv->ctlr, &ampl_info)) {
+			ret = -ENODEV;
+			dev_err(priv->dev, "Failed to create left amp slave\n");
+			goto err;
+		}
+
+		if (!spi_new_device(priv->ctlr, &ampr_info)) {
+			ret = -ENODEV;
+			dev_err(priv->dev, "Failed to create right amp slave\n");
+			goto err;
+		}
+	}
+
+	return 0;
+
+err:
+	if (has_sidecar)
+		software_node_unregister(&cs42l43_gpiochip_swnode);
+
 	return ret;
 }
 
+static int cs42l43_spi_remove(struct platform_device *pdev)
+{
+	struct cs42l43 *cs42l43 = dev_get_drvdata(pdev->dev.parent);
+	struct fwnode_handle *fwnode = dev_fwnode(cs42l43->dev);
+	bool has_sidecar = cs42l43_has_sidecar(fwnode);
+
+	if (has_sidecar)
+		software_node_unregister(&cs42l43_gpiochip_swnode);
+
+	return 0;
+};
+
 static const struct platform_device_id cs42l43_spi_id_table[] = {
 	{ "cs42l43-spi", },
 	{}
@@ -288,6 +437,7 @@ static struct platform_driver cs42l43_spi_driver = {
 	},
 	.probe		= cs42l43_spi_probe,
 	.id_table	= cs42l43_spi_id_table,
+	.remove		= cs42l43_spi_remove,
 };
 module_platform_driver(cs42l43_spi_driver);
 
-- 
2.39.2

Re: [PATCH 3/3] spi: cs42l43: Add bridged cs35l56 amplifiers

[kernel test robot]

Hi Charles,

kernel test robot noticed the following build warnings:

[auto build test WARNING on broonie-spi/for-next]
[also build test WARNING on brgl/gpio/for-next linus/master v6.9-rc1 next-20240327]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Charles-Keepax/gpio-swnode-Add-ability-to-specify-native-chip-selects-for-SPI/20240326-221422
base:   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next
patch link:    https://lore.kernel.org/r/20240326141108.1079993-4-ckeepax%40opensource.cirrus.com
patch subject: [PATCH 3/3] spi: cs42l43: Add bridged cs35l56 amplifiers
config: sh-randconfig-r121-20240327 (https://download.01.org/0day-ci/archive/20240328/202403280258.rjWikSAr-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 13.2.0
reproduce: (https://download.01.org/0day-ci/archive/20240328/202403280258.rjWikSAr-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202403280258.rjWikSAr-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> drivers/spi/spi-cs42l43.c:48:28: sparse: sparse: symbol 'ampr' was not declared. Should it be static?
>> drivers/spi/spi-cs42l43.c:52:23: sparse: sparse: symbol 'ampl_info' was not declared. Should it be static?
>> drivers/spi/spi-cs42l43.c:61:23: sparse: sparse: symbol 'ampr_info' was not declared. Should it be static?
   drivers/spi/spi-cs42l43.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/slab.h, ...):
   include/linux/page-flags.h:242:46: sparse: sparse: self-comparison always evaluates to false
   include/linux/page-flags.h:242:46: sparse: sparse: self-comparison always evaluates to false

vim +/ampr +48 drivers/spi/spi-cs42l43.c

    47	
  > 48	const struct software_node ampr = {
    49		.name			= "cs35l56-right",
    50	};
    51	
  > 52	struct spi_board_info ampl_info = {
    53		.modalias		= "cs35l56",
    54		.max_speed_hz		= 2000000,
    55		.chip_select		= 0,
    56		.mode			= SPI_MODE_0,
    57		.swnode			= &ampl,
    58		.use_fwnode_name	= true,
    59	};
    60	
  > 61	struct spi_board_info ampr_info = {
    62		.modalias		= "cs35l56",
    63		.max_speed_hz		= 2000000,
    64		.chip_select		= 1,
    65		.mode			= SPI_MODE_0,
    66		.swnode			= &ampr,
    67		.use_fwnode_name	= true,
    68	};
    69	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 3/3] spi: cs42l43: Add bridged cs35l56 amplifiers

[kernel test robot]

Hi Charles,

kernel test robot noticed the following build warnings:

[auto build test WARNING on broonie-spi/for-next]
[also build test WARNING on brgl/gpio/for-next linus/master v6.9-rc1 next-20240328]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Charles-Keepax/gpio-swnode-Add-ability-to-specify-native-chip-selects-for-SPI/20240326-221422
base:   https://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git for-next
patch link:    https://lore.kernel.org/r/20240326141108.1079993-4-ckeepax%40opensource.cirrus.com
patch subject: [PATCH 3/3] spi: cs42l43: Add bridged cs35l56 amplifiers
config: sh-randconfig-r121-20240327 (https://download.01.org/0day-ci/archive/20240328/202403282033.oFvCtRT7-lkp@intel.com/config)
compiler: sh4-linux-gcc (GCC) 13.2.0
reproduce: (https://download.01.org/0day-ci/archive/20240328/202403282033.oFvCtRT7-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202403282033.oFvCtRT7-lkp@intel.com/

sparse warnings: (new ones prefixed by >>)
>> drivers/spi/spi-cs42l43.c:48:28: sparse: sparse: symbol 'ampr' was not declared. Should it be static?
>> drivers/spi/spi-cs42l43.c:52:23: sparse: sparse: symbol 'ampl_info' was not declared. Should it be static?
>> drivers/spi/spi-cs42l43.c:61:23: sparse: sparse: symbol 'ampr_info' was not declared. Should it be static?
   drivers/spi/spi-cs42l43.c: note: in included file (through include/linux/mmzone.h, include/linux/gfp.h, include/linux/slab.h, ...):
   include/linux/page-flags.h:242:46: sparse: sparse: self-comparison always evaluates to false
   include/linux/page-flags.h:242:46: sparse: sparse: self-comparison always evaluates to false

vim +/ampr +48 drivers/spi/spi-cs42l43.c

    47	
  > 48	const struct software_node ampr = {
    49		.name			= "cs35l56-right",
    50	};
    51	
  > 52	struct spi_board_info ampl_info = {
    53		.modalias		= "cs35l56",
    54		.max_speed_hz		= 2000000,
    55		.chip_select		= 0,
    56		.mode			= SPI_MODE_0,
    57		.swnode			= &ampl,
    58		.use_fwnode_name	= true,
    59	};
    60	
  > 61	struct spi_board_info ampr_info = {
    62		.modalias		= "cs35l56",
    63		.max_speed_hz		= 2000000,
    64		.chip_select		= 1,
    65		.mode			= SPI_MODE_0,
    66		.swnode			= &ampr,
    67		.use_fwnode_name	= true,
    68	};
    69	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Linus Walleij]

On Tue, Mar 26, 2024 at 3:11 PM Charles Keepax
<ckeepax@opensource.cirrus.com> wrote:

> SPI devices can specify a cs-gpios property to enumerate their
> chip selects. Under device tree, a zero entry in this property can
> be used to specify that a particular chip select is using the SPI
> controllers native chip select, for example:
>
>         cs-gpios = <&gpio1 0 0>, <0>;
>
> Here the second chip select is native. However, when using swnodes
> there is currently no way to specify a native chip select. The
> proposal here is to register a swnode_gpio_undefined software node,
> that can be specified to allow the indication of a native chip
> select. For example:
>
> static const struct software_node_ref_args device_cs_refs[] = {
>         {
>                 .node  = &device_gpiochip_swnode,
>                 .nargs = 2,
>                 .args  = { 0, GPIO_ACTIVE_LOW },
>         },
>         {
>                 .node  = &swnode_gpio_undefined,
>                 .nargs = 0,
>         },
> };
>
> Register the swnode as the gpiolib is initialised and
> check in swnode_get_gpio_device if the returned node matches
> swnode_gpio_undefined and return -ENOENT, which matches the behaviour
> of the device tree system when it encounters a 0 phandle.
>
> Signed-off-by: Charles Keepax <ckeepax@opensource.cirrus.com>

Hm that's an interesting corner case.

> +const struct software_node swnode_gpio_undefined = {
> +       .name = "gpio-internal-undefined",
> +};
> +EXPORT_SYMBOL_GPL(swnode_gpio_undefined);

This needs a comment in the code telling exactly why this is here.
It is also taking up space and code here on systems that have no use
for it, so I wonder if it is possible to make this optional.

> +       if (!strcmp(gdev_node->name, "gpio-internal-undefined"))
> +               return ERR_PTR(-ENOENT);

This needs a comment stating why this check is here, it's not
obvious.

Yours,
Linus Walleij

Re: [PATCH 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Charles Keepax]

On Thu, Apr 04, 2024 at 10:16:35AM +0200, Linus Walleij wrote:
> On Tue, Mar 26, 2024 at 3:11 PM Charles Keepax
> <ckeepax@opensource.cirrus.com> wrote:
> > +const struct software_node swnode_gpio_undefined = {
> > +       .name = "gpio-internal-undefined",
> > +};
> > +EXPORT_SYMBOL_GPL(swnode_gpio_undefined);
> 
> This needs a comment in the code telling exactly why this is here.
> It is also taking up space and code here on systems that have no use
> for it, so I wonder if it is possible to make this optional.
> 

Happy to add the comment, less sure about how to make it
optional. I could ifdef it based the SPI config, but whilst that
is the current user the mechanism feels like it is more generic
than that and could be used in other bindings as well.

> > +       if (!strcmp(gdev_node->name, "gpio-internal-undefined"))
> > +               return ERR_PTR(-ENOENT);
> 
> This needs a comment stating why this check is here, it's not
> obvious.

Happy to add a comment here as well.

Thanks,
Charles

Re: [PATCH 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Linus Walleij]

On Mon, Apr 8, 2024 at 3:21 PM Charles Keepax
<ckeepax@opensource.cirrus.com> wrote:
> On Thu, Apr 04, 2024 at 10:16:35AM +0200, Linus Walleij wrote:
> > On Tue, Mar 26, 2024 at 3:11 PM Charles Keepax
> > <ckeepax@opensource.cirrus.com> wrote:
> > > +const struct software_node swnode_gpio_undefined = {
> > > +       .name = "gpio-internal-undefined",
> > > +};
> > > +EXPORT_SYMBOL_GPL(swnode_gpio_undefined);
> >
> > This needs a comment in the code telling exactly why this is here.
> > It is also taking up space and code here on systems that have no use
> > for it, so I wonder if it is possible to make this optional.
> >
>
> Happy to add the comment, less sure about how to make it
> optional. I could ifdef it based the SPI config, but whilst that
> is the current user the mechanism feels like it is more generic
> than that and could be used in other bindings as well.

That's a fair point.
Maybe a new bool Kconfig symbol that the SPI drivers or
other potential users can select?

Yours,
Linus Walleij

Re: [PATCH 1/3] gpio: swnode: Add ability to specify native chip selects for SPI

[Charles Keepax]

On Tue, Apr 09, 2024 at 09:12:01AM +0200, Linus Walleij wrote:
> On Mon, Apr 8, 2024 at 3:21 PM Charles Keepax
> <ckeepax@opensource.cirrus.com> wrote:
> > On Thu, Apr 04, 2024 at 10:16:35AM +0200, Linus Walleij wrote:
> > > On Tue, Mar 26, 2024 at 3:11 PM Charles Keepax
> > > <ckeepax@opensource.cirrus.com> wrote:
> > > > +const struct software_node swnode_gpio_undefined = {
> > > > +       .name = "gpio-internal-undefined",
> > > > +};
> > > > +EXPORT_SYMBOL_GPL(swnode_gpio_undefined);
> > >
> > > This needs a comment in the code telling exactly why this is here.
> > > It is also taking up space and code here on systems that have no use
> > > for it, so I wonder if it is possible to make this optional.
> > >
> >
> > Happy to add the comment, less sure about how to make it
> > optional. I could ifdef it based the SPI config, but whilst that
> > is the current user the mechanism feels like it is more generic
> > than that and could be used in other bindings as well.
> 
> That's a fair point.
> Maybe a new bool Kconfig symbol that the SPI drivers or
> other potential users can select?
> 

OK I will add a Kconfig to enable this feature.

Thanks,
Charles