linux-kernel - [PATCH RFT/RFC 1/2] gpiolib: support "undefined" GPIO machine lookup

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Message-Id: <20251119-cs42l43-gpio-lookup-v1-1-029b1d9e1843@linaro.org>
Date: Wed, 19 Nov 2025 16:21:28 +0100
From: Bartosz Golaszewski <brgl@...ev.pl>
To: Linus Walleij <linus.walleij@...aro.org>, 
 Bartosz Golaszewski <brgl@...ev.pl>, David Rhodes <david.rhodes@...rus.com>, 
 Richard Fitzgerald <rf@...nsource.cirrus.com>, Lee Jones <lee@...nel.org>, 
 Mark Brown <broonie@...nel.org>, 
 Maciej Strozek <mstrozek@...nsource.cirrus.com>, 
 Charles Keepax <ckeepax@...nsource.cirrus.com>, 
 Andy Shevchenko <andy@...nel.org>, Philipp Zabel <p.zabel@...gutronix.de>
Cc: linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org, 
 linux-sound@...r.kernel.org, patches@...nsource.cirrus.com, 
 linux-spi@...r.kernel.org, 
 Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: [PATCH RFT/RFC 1/2] gpiolib: support "undefined" GPIO machine
 lookup

From: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>

SPI devices can specify a cs-gpios property to enumerate their chip
selects. In 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. Allow users to pass
ERR_PTR(-ENOENT) as the key field in struct gpiod_lookup, indicating a
native chip select.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
---
 drivers/gpio/gpiolib.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 91e0c384f34ae5c0ed61ccd3a978685d4f72e867..dbb5f7fe7b661979f559fcd32ad6e1c463431a18 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -4557,6 +4557,9 @@ static struct gpio_desc *gpiod_find(struct device *dev, const char *con_id,
 		if (p->con_id && (!con_id || strcmp(p->con_id, con_id)))
 			continue;
 
+		if (p->key == PTR_ERR(-ENOENT))
+			return ERR_PTR(-ENOENT);
+
 		if (p->chip_hwnum == U16_MAX) {
 			desc = gpio_name_to_desc(p->key);
 			if (desc) {

-- 
2.51.0