Re: [PATCH] gpiolib: Remove big fat warning in gpiochip_get_direction()

[Bartosz Golaszewski]

On Tue, Jun 2, 2026 at 1:31 PM Christophe Leroy (CS GROUP)
<chleroy@xxxxxxxxxx> wrote:
>
> Since kernel v6.15 the following big fat warning is encountered when
> reading /sys/kernel/debug/gpio, leading to kernel latency while
> emiting the warning, and panicing on systems configured to panic on
> warnings.
>
>   ------------[ cut here ]------------
>   WARNING: drivers/gpio/gpiolib.c:423 at gpiochip_get_direction+0x3c/0x48, CPU#0: cat/12531
>   CPU: 0 UID: 0 PID: 12531 Comm: cat Tainted: G        W           7.0.10-gitc72c39~-01802-g28c351659258 #27 PREEMPT
>   Tainted: [W]=WARN
>   Hardware name: MIAE 8xx 0x500000 CMPC885
>   NIP:  c043c2f8 LR: c043d740 CTR: 00000000
>   REGS: ca89bc20 TRAP: 0700   Tainted: G        W            (7.0.10-gitc72c39~-01802-g28c351659258)
>   MSR:  00029032 <EE,ME,IR,DR,RI>  CR: 24004884  XER: 00000302
>
>   GPR00: c043f3f0 ca89bce0 c3278000 c20b5f20 0000000d 00000002 00000000 c0a76208
>   GPR08: 00000001 00000000 cccccccd c313d830 84004884 100d815e c0a76208 c0a761f8
>   GPR16: c0a761f4 c0a76278 1048834c 10488350 c21c0b04 c21c0d93 c0a5fb74 c313d848
>   GPR24: c20b5f20 c21c0d94 00000000 00000000 c21c0d94 00000000 c21c0c00 c21c0b04
>   NIP [c043c2f8] gpiochip_get_direction+0x3c/0x48
>   LR [c043d740] gpiod_get_direction+0xa0/0x170
>   Call Trace:
>   [ca89bce0] [c28157e8] 0xc28157e8 (unreliable)
>   [ca89bd10] [c043f3f0] gpiolib_seq_show+0x370/0x524
>   [ca89bd90] [c021dd1c] seq_read_iter+0x174/0x618
>   [ca89bdd0] [c021e260] seq_read+0xa0/0xd0
>   [ca89be40] [c031063c] full_proxy_read+0x80/0xc4
>   [ca89be70] [c01df3e0] vfs_read+0xb4/0x35c
>   [ca89bee0] [c01e0180] ksys_read+0x8c/0x15c
>   [ca89bf10] [c000dc94] system_call_exception+0x88/0x154
>   [ca89bf30] [c00110a8] ret_from_syscall+0x0/0x28
>   ---- interrupt: c00 at 0xfc629e8
>   NIP:  0fc629e8 LR: 0fc62a34 CTR: 00000000
>   REGS: ca89bf40 TRAP: 0c00   Tainted: G        W            (7.0.10-gitc72c39~-01802-g28c351659258)
>   MSR:  0000d032 <EE,PR,ME,IR,DR,RI>  CR: 28004884  XER: 00000302
>
>   GPR00: 00000003 7f8df6a0 77e37540 00000003 7f8df6e8 00001000 00000000 00000000
>   GPR08: 00000000 7f8e3efc 00000000 7f8e06f0 7f8e3efc 100d815e 7fe70e10 100d0000
>   GPR16: 100d0000 00000001 1048834c 10488350 22000882 77e3fe68 1000596c 77e40b28
>   GPR24: 00000000 28004884 01000000 00001000 7f8df6e8 00000003 0fde36a0 00000000
>   NIP [0fc629e8] 0xfc629e8
>   LR [0fc62a34] 0xfc62a34
>   ---- interrupt: c00
>   Code: 9421fff0 7c0802a6 90010014 7d2903a6 4e800421 2c030001 40810008 3860ffcc 80010014 38210010 7c0803a6 4e800020 <0fe00000> 3860ffa1 4e800020 81230020
>   ---[ end trace 0000000000000000 ]---
>
> This is due to a WARN_ON() added by commit ec2cceadfae7 ("gpiolib:
> normalize the return value of gc->get() on behalf of buggy drivers")
> when the gpiochip doesn't implement get_direction() function. But
> according to the documentation in <linux/gpio/driver.h> implementing
> get_direction() is only a recommendation, not a requirement. And
> regarless, WARN_ON() has no added value here, dumping all CPU
> registers doesn't give any useful information for that case.
>
> Lower it to a simple warn_on_once() message.
>
> Fixes: ec2cceadfae7 ("gpiolib: normalize the return value of gc->get() on behalf of buggy drivers")
> Signed-off-by: Christophe Leroy (CS GROUP) <chleroy@xxxxxxxxxx>
> ---

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What driver are you using?

Bart