linux-kernel - [PATCH v2] gpio: mxc: configure dynamic GPIO base for CONFIG_GPIO

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Message-Id: <20250507-b4-imx-gpio-base-warning-v2-1-d43d09e2c6bf@pengutronix.de>
Date: Wed, 07 May 2025 15:07:25 +0200
From: Ahmad Fatoum <a.fatoum@...gutronix.de>
To: Linus Walleij <linus.walleij@...aro.org>, 
 Bartosz Golaszewski <brgl@...ev.pl>, Shawn Guo <shawnguo@...nel.org>, 
 Sascha Hauer <s.hauer@...gutronix.de>, 
 Pengutronix Kernel Team <kernel@...gutronix.de>, 
 Fabio Estevam <festevam@...il.com>
Cc: linux-gpio@...r.kernel.org, 
 Dario Binacchi <dario.binacchi@...rulasolutions.com>, 
 Haibo Chen <haibo.chen@....com>, 
 Catalin Popescu <catalin.popescu@...ca-geosystems.com>, imx@...ts.linux.dev, 
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org, 
 Ahmad Fatoum <a.fatoum@...gutronix.de>
Subject: [PATCH v2] gpio: mxc: configure dynamic GPIO base for
 CONFIG_GPIO_SYSFS=n

i.MX GPIO numbering has been deterministic since commit 7e6086d9e54a
("gpio/mxc: specify gpio base for device tree probe"), a year after
device tree support was first added back in 2011.

Reverting to dynamically allocated GPIO base now would break most
systems making use of the sysfs API. These systems will be eventually
broken by the removal of the sysfs API, but that would result in GPIO
scripts not working instead of essentially toggling at random according
to probe order, which would happen if we unconditionally set base to -1.

Yet, the warning is annoying and has resulted in many rejected attempts
to remove it over the years[1][2][3].

As the i.MX GPIO driver is device tree only, GPIO_SYSFS is the only
consumer of the deterministic GPIO numbering. Let's therefore restrict the
static base and the warning that comes with it to configurations
with CONFIG_GPIO_SYSFS enabled.

[1]: https://lore.kernel.org/all/20230226205319.1013332-1-dario.binacchi@amarulasolutions.com/
[2]: https://lore.kernel.org/all/20230506085928.933737-2-haibo.chen@nxp.com/
[3]: https://lore.kernel.org/all/20241121145515.3087855-1-catalin.popescu@leica-geosystems.com/

Signed-off-by: Ahmad Fatoum <a.fatoum@...gutronix.de>
---
This was one result of the discussion with Bartosz at FOSDEM 2025.
---
Changes in v2:
- drop warning opt-out flag
- set a dynamic base only if sysfs support is disabled.
- drop unrelated driver cleanup separately picked by Bartosz
- Link to v1: https://lore.kernel.org/r/20250113-b4-imx-gpio-base-warning-v1-0-0a28731a5cf6@pengutronix.de
---
 drivers/gpio/gpio-mxc.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/gpio/gpio-mxc.c b/drivers/gpio/gpio-mxc.c
index 619b6fb9d833a4bb94a93b4209f01b49ad1cbdb0..38504c9486b05802a792367111c9d71dc08bdd16 100644
--- a/drivers/gpio/gpio-mxc.c
+++ b/drivers/gpio/gpio-mxc.c
@@ -490,7 +490,14 @@ static int mxc_gpio_probe(struct platform_device *pdev)
 	port->gc.request = mxc_gpio_request;
 	port->gc.free = mxc_gpio_free;
 	port->gc.to_irq = mxc_gpio_to_irq;
-	port->gc.base = of_alias_get_id(np, "gpio") * 32;
+	/*
+	 * Driver is DT-only, so a fixed base needs only be maintained for legacy
+	 * userspace with sysfs interface.
+	 */
+	if (IS_ENABLED(CONFIG_GPIO_SYSFS))
+		port->gc.base = of_alias_get_id(np, "gpio") * 32;
+	else /* silence boot time warning */
+		port->gc.base = -1;
 
 	err = devm_gpiochip_add_data(&pdev->dev, &port->gc, port);
 	if (err)

---
base-commit: 92a09c47464d040866cf2b4cd052bc60555185fb
change-id: 20250113-b4-imx-gpio-base-warning-4f9ae89887d0

Best regards,
-- 
Ahmad Fatoum <a.fatoum@...gutronix.de>