Unverified Commit 9d50f95b authored by Charles Keepax's avatar Charles Keepax Committed by Mark Brown
Browse files

gpio: swnode: Add ability to specify native chip selects for SPI 



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.

Reviewed-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Reviewed-by: default avatarAndy Shevchenko <andy@kernel.org>
Signed-off-by: default avatarCharles Keepax <ckeepax@opensource.cirrus.com>
Link: https://lore.kernel.org/r/20240416100904.3738093-2-ckeepax@opensource.cirrus.com


Signed-off-by: default avatarMark Brown <broonie@kernel.org>
parent fec50db7

drivers/gpio/Kconfig

+9 −0
Original line number Diff line number Diff line
@@ -103,6 +103,15 @@ config GPIO_REGMAP 
	select REGMAP

	tristate



config GPIO_SWNODE_UNDEFINED

	bool

	help

	  This adds a special place holder for software nodes to contain an

	  undefined GPIO reference, this is primarily used by SPI to allow a

	  list of GPIO chip selects to mark a certain chip select as being

	  controlled the SPI device's internal chip select mechanism and not

	  a GPIO.



# put drivers in the right section, in alphabetical order



# This symbol is selected by both I2C and SPI expanders

drivers/gpio/gpiolib-swnode.c

+44 −0
Original line number Diff line number Diff line
@@ -4,8 +4,13 @@ 
 *

 * Copyright 2022 Google LLC

 */



#define pr_fmt(fmt) "gpiolib: swnode: " fmt



#include <linux/err.h>

#include <linux/errno.h>

#include <linux/export.h>

#include <linux/init.h>

#include <linux/kernel.h>

#include <linux/printk.h>

#include <linux/property.h>
@@ -17,6 +22,8 @@ 
#include "gpiolib.h"

#include "gpiolib-swnode.h"



#define GPIOLIB_SWNODE_UNDEFINED_NAME "swnode-gpio-undefined"



static void swnode_format_propname(const char *con_id, char *propname,

				   size_t max_size)

{
@@ -40,6 +47,14 @@ static struct gpio_device *swnode_get_gpio_device(struct fwnode_handle *fwnode) 
	if (!gdev_node || !gdev_node->name)

		return ERR_PTR(-EINVAL);



	/*

	 * Check for a special node that identifies undefined GPIOs, this is

	 * primarily used as a key for internal chip selects in SPI bindings.

	 */

	if (IS_ENABLED(CONFIG_GPIO_SWNODE_UNDEFINED) &&

	    !strcmp(gdev_node->name, GPIOLIB_SWNODE_UNDEFINED_NAME))

		return ERR_PTR(-ENOENT);



	gdev = gpio_device_find_by_label(gdev_node->name);

	return gdev ?: ERR_PTR(-EPROBE_DEFER);

}
@@ -121,3 +136,32 @@ int swnode_gpio_count(const struct fwnode_handle *fwnode, const char *con_id) 


	return count ?: -ENOENT;

}



#if IS_ENABLED(CONFIG_GPIO_SWNODE_UNDEFINED)

/*

 * A special node that identifies undefined GPIOs, this is primarily used as

 * a key for internal chip selects in SPI bindings.

 */

const struct software_node swnode_gpio_undefined = {

	.name = GPIOLIB_SWNODE_UNDEFINED_NAME,

};

EXPORT_SYMBOL_NS_GPL(swnode_gpio_undefined, GPIO_SWNODE);



static int __init swnode_gpio_init(void)

{

	int ret;



	ret = software_node_register(&swnode_gpio_undefined);

	if (ret < 0)

		pr_err("failed to register swnode: %d\n", ret);



	return ret;

}

subsys_initcall(swnode_gpio_init);



static void __exit swnode_gpio_cleanup(void)

{

	software_node_unregister(&swnode_gpio_undefined);

}

__exitcall(swnode_gpio_cleanup);

#endif

include/linux/gpio/property.h

+4 −0
Original line number Diff line number Diff line
@@ -5,7 +5,11 @@ 
#include <dt-bindings/gpio/gpio.h> /* for GPIO_* flags */

#include <linux/property.h>



struct software_node;



#define PROPERTY_ENTRY_GPIO(_name_, _chip_node_, _idx_, _flags_) \

	PROPERTY_ENTRY_REF(_name_, _chip_node_, _idx_, _flags_)



extern const struct software_node swnode_gpio_undefined;



#endif /* __LINUX_GPIO_PROPERTY_H */