[PATCH] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[PATCH] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[Shreeya Patel]

We are racing the registering of .to_irq when probing the
i2c driver. This results in random failure of touchscreen
devices.

Following errors could be seen in dmesg logs when gc->to_irq is NULL

[2.101857] i2c_hid i2c-FTS3528:00: HID over i2c has not been provided an Int IRQ
[2.101953] i2c_hid: probe of i2c-FTS3528:00 failed with error -22

To avoid this situation, defer probing until to_irq is registered.

This issue has been reported many times in past and people have been
using workarounds like changing the pinctrl_amd to built-in instead
of loading it as a module or by adding a softdep for pinctrl_amd into
the config file.

References :-
https://bugzilla.kernel.org/show_bug.cgi?id=209413
https://github.com/Syniurge/i2c-amd-mp2/issues/3

Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>
---
 drivers/gpio/gpiolib.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
index 27c07108496d..fc0ba85f4c45 100644
--- a/drivers/gpio/gpiolib.c
+++ b/drivers/gpio/gpiolib.c
@@ -3084,7 +3084,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
 
 		return retirq;
 	}
-	return -ENXIO;
+	return -EPROBE_DEFER;
 }
 EXPORT_SYMBOL_GPL(gpiod_to_irq);
 
-- 
2.30.2

Re: [PATCH] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[Linus Walleij]

On Thu, Oct 14, 2021 at 1:05 PM Shreeya Patel
<shreeya.patel@collabora.com> wrote:

> We are racing the registering of .to_irq when probing the
> i2c driver. This results in random failure of touchscreen
> devices.
>
> Following errors could be seen in dmesg logs when gc->to_irq is NULL
>
> [2.101857] i2c_hid i2c-FTS3528:00: HID over i2c has not been provided an Int IRQ
> [2.101953] i2c_hid: probe of i2c-FTS3528:00 failed with error -22
>
> To avoid this situation, defer probing until to_irq is registered.
>
> This issue has been reported many times in past and people have been
> using workarounds like changing the pinctrl_amd to built-in instead
> of loading it as a module or by adding a softdep for pinctrl_amd into
> the config file.
>
> References :-
> https://bugzilla.kernel.org/show_bug.cgi?id=209413
> https://github.com/Syniurge/i2c-amd-mp2/issues/3
>
> Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>

I understand the issue.

There is one problem.

> @@ -3084,7 +3084,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
>
>                 return retirq;
>         }
> -       return -ENXIO;
> +       return -EPROBE_DEFER;

If you after five minutes plug in a USB FTDI or similar UART thing
with a GPIO expander, and someone request an IRQ from
one of those lines (they do not support interrupts), why should
it return -EPROBE_DEFER?

The point is that I think this will in certain circumstances return
a bogus error.

We cannot merge this other than with a fat comment above:

/*
 * This is semantically WRONG because the -EPROBE_DEFER
 * is really just applicable during system bring-up.
 */
return -EPROBE_DEFER;

Can we use some kind of late_initcall() to just switch this over
to -ENXIO after a while?

Yours,
Linus Walleij

Re: [PATCH] gpio: Return EPROBE_DEFER if gc->to_irq is NULL

[Shreeya Patel]

On 14/10/21 10:21 pm, Linus Walleij wrote:
> On Thu, Oct 14, 2021 at 1:05 PM Shreeya Patel
> <shreeya.patel@collabora.com> wrote:
>
>> We are racing the registering of .to_irq when probing the
>> i2c driver. This results in random failure of touchscreen
>> devices.
>>
>> Following errors could be seen in dmesg logs when gc->to_irq is NULL
>>
>> [2.101857] i2c_hid i2c-FTS3528:00: HID over i2c has not been provided an Int IRQ
>> [2.101953] i2c_hid: probe of i2c-FTS3528:00 failed with error -22
>>
>> To avoid this situation, defer probing until to_irq is registered.
>>
>> This issue has been reported many times in past and people have been
>> using workarounds like changing the pinctrl_amd to built-in instead
>> of loading it as a module or by adding a softdep for pinctrl_amd into
>> the config file.
>>
>> References :-
>> https://bugzilla.kernel.org/show_bug.cgi?id=209413
>> https://github.com/Syniurge/i2c-amd-mp2/issues/3
>>
>> Signed-off-by: Shreeya Patel <shreeya.patel@collabora.com>
> I understand the issue.
>
> There is one problem.
>
>> @@ -3084,7 +3084,7 @@ int gpiod_to_irq(const struct gpio_desc *desc)
>>
>>                  return retirq;
>>          }
>> -       return -ENXIO;
>> +       return -EPROBE_DEFER;
> If you after five minutes plug in a USB FTDI or similar UART thing
> with a GPIO expander, and someone request an IRQ from
> one of those lines (they do not support interrupts), why should
> it return -EPROBE_DEFER?
>
> The point is that I think this will in certain circumstances return
> a bogus error.

I was worried about the same but didn't really know under what scenario 
this could occur.
Thanks for pointing this out.

>
> We cannot merge this other than with a fat comment above:
>
> /*
>   * This is semantically WRONG because the -EPROBE_DEFER
>   * is really just applicable during system bring-up.
>   */
> return -EPROBE_DEFER;
>
> Can we use some kind of late_initcall() to just switch this over
> to -ENXIO after a while?


I have sent a v2 which tries to fix this in an easy way. Let me know 
what do you
think about that approach or else we could also think about using 
late_initcall().



Thanks,
Shreeya Patel


> Yours,
> Linus Walleij