linux-kernel - Re: [PATCH] leds: simatic-ipc-leds-gpio: do not run into endless EPROBE

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Date:   Thu, 2 Feb 2023 20:47:30 +0100
From:   Henning Schild <henning.schild@...mens.com>
To:     Pavel Machek <pavel@....cz>, Lee Jones <lee@...nel.org>,
        Hans de Goede <hdegoede@...hat.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        <linux-leds@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] leds: simatic-ipc-leds-gpio: do not run into endless
 EPROBE_DEFER loop

Am Wed, 25 Jan 2023 19:17:11 +0100
schrieb Henning Schild <henning.schild@...mens.com>:

> Should the driver providing our GPIOs not be available we used to
> return -EPORBE_DEFER out of the probe function and cause a
> potentially endless loop that also printed a lot to the kernel log.
> 
> ...
> leds-gpio leds-gpio: cannot find GPIO chip igpio-f7188x-2, deferring
> leds-gpio leds-gpio: Skipping unavailable LED gpio 0 (red:status-1)
> ...
> 
> The "leds-gpio" just ignores all entries and would never try again
> even if the GPIOs show up later. But our extra two GPIOs could cause
> that loop, in which we would even register/unregister "leds-gpio" and
> cause all the printing.
> 
> If any of those two extra GPIOs is not there, return with -ENODEV
> instead of -EPROBE_DEFER.

This is a really bad idea. The real fix for the future will be to
write individual drivers which clearly describe their dep chains.

This patch should not be merged.

Henning
 
> Fixes: a6c80bec3c93 ("leds: simatic-ipc-leds-gpio: Add GPIO version
> of Siemens driver") Signed-off-by: Henning Schild
> <henning.schild@...mens.com> ---
>  drivers/leds/simple/simatic-ipc-leds-gpio.c | 29
> +++++++++------------ 1 file changed, 13 insertions(+), 16
> deletions(-)
> 
> diff --git a/drivers/leds/simple/simatic-ipc-leds-gpio.c
> b/drivers/leds/simple/simatic-ipc-leds-gpio.c index
> 07f0d79d604d..4e2595e684c6 100644 ---
> a/drivers/leds/simple/simatic-ipc-leds-gpio.c +++
> b/drivers/leds/simple/simatic-ipc-leds-gpio.c @@ -74,14 +74,13 @@
> static int simatic_ipc_leds_gpio_probe(struct platform_device *pdev)
> const struct simatic_ipc_platform *plat = pdev->dev.platform_data;
> struct gpio_desc *gpiod; int err;
> +	int i;
>  
>  	switch (plat->devmode) {
>  	case SIMATIC_IPC_DEVICE_127E:
>  		simatic_ipc_led_gpio_table =
> &simatic_ipc_led_gpio_table_127e; break;
>  	case SIMATIC_IPC_DEVICE_227G:
> -		if (!IS_ENABLED(CONFIG_GPIO_F7188X))
> -			return -ENODEV;
>  		request_module("gpio-f7188x");
>  		simatic_ipc_led_gpio_table =
> &simatic_ipc_led_gpio_table_227g; break;
> @@ -99,21 +98,19 @@ static int simatic_ipc_leds_gpio_probe(struct
> platform_device *pdev) goto out;
>  	}
>  
> -	/* PM_BIOS_BOOT_N */
> -	gpiod = gpiod_get_index(&simatic_leds_pdev->dev, NULL, 6,
> GPIOD_OUT_LOW);
> -	if (IS_ERR(gpiod)) {
> -		err = PTR_ERR(gpiod);
> -		goto out;
> -	}
> -	gpiod_put(gpiod);
> -
> -	/* PM_WDT_OUT */
> -	gpiod = gpiod_get_index(&simatic_leds_pdev->dev, NULL, 7,
> GPIOD_OUT_LOW);
> -	if (IS_ERR(gpiod)) {
> -		err = PTR_ERR(gpiod);
> -		goto out;
> +	for (i = 0; i < 2; i++) {
> +		gpiod = gpiod_get_index(&simatic_leds_pdev->dev,
> NULL,
> +
> ARRAY_SIZE(simatic_ipc_gpio_leds) + i, GPIOD_OUT_LOW);
> +		if (IS_ERR(gpiod)) {
> +			err = PTR_ERR(gpiod);
> +			if (err == -EPROBE_DEFER) {
> +				dev_err(&pdev->dev, "GPIO driver
> seems missing\n");
> +				err = -ENODEV;
> +			}
> +			goto out;
> +		}
> +		gpiod_put(gpiod);
>  	}
> -	gpiod_put(gpiod);
>  
>  	return 0;
>  out: