Re: [PATCH] gpio: Return EPROBE_DEFER if gc->to_irq is NULL
From: Linus Walleij <hidden>
Date: 2021-10-14 16:51:55
Also in:
linux-i2c, lkml
On Thu, Oct 14, 2021 at 1:05 PM Shreeya Patel [off-list ref] 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 <redacted>
I understand the issue. There is one problem.
quoted hunk ↗ jump to hunk
@@ -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