"gpiolib: remove redundant callback check" causes regression when gpio_chip.get_direction callback is not implemented

[Frank Wunderlich]

Hi

i stumbled over your commit 471e998c0e31 "gpiolib: remove redundant callback check" in 
kernel 7.0 (6.19-rc6+ should be affected) because i get some traces on my mt7988 board
when calling "cat /sys/kernel/debug/gpio":

[   33.903162] gpio-chip: pinctrl_moore base: 200 offset: 0
[   33.908489] ------------[ cut here ]------------
[   33.913095] WARNING: drivers/gpio/gpiolib.c:424 at gpiochip_get_direction+0x60/0x78, CPU#0: cat/3421
[   33.922216] Modules linked in:
[   33.925262] CPU: 0 UID: 0 PID: 3421 Comm: cat Tainted: G        W           7.0.0-rc6-bpi-r4-rc6 #9 PREEMPTLAZY 
[   33.935423] Tainted: [W]=WARN
[   33.938380] Hardware name: Bananapi BPI-R4 Pro 8X (DT)
[   33.943506] pstate: 60400005 (nZCv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
[   33.950454] pc : gpiochip_get_direction+0x60/0x78
[   33.955148] lr : gpiochip_get_direction+0x30/0x78
[   33.959841] sp : ffffffc088463ae0
[   33.963145] x29: ffffffc088463ae0 x28: ffffff80c02e1c17 x27: ffffff80c01073f0
[   33.970271] x26: ffffffc08123e448 x25: ffffff80c02e1c18 x24: ffffff80c01682a0
[   33.977397] x23: 0000000000000000 x22: ffffff80c02e1c18 x21: ffffff80c02e1800
[   33.984523] x20: 0000000000000015 x19: ffffff80c01682a0 x18: 00000000ffffffff
[   33.991649] x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000006
[   33.998774] x14: 00000000ffffffea x13: ffffffc088463858 x12: ffffffc081979ce8
[   34.005901] x11: 0000000000000001 x10: 0000000000000001 x9 : 0000000000017fe8
[   34.013027] x8 : ffffffc081921c70 x7 : c0000000ffffefff x6 : 0000000000057fa8
[   34.020154] x5 : ffffff80ff746688 x4 : 0000000000000000 x3 : 0000000000000000
[   34.027280] x2 : 0000000000000000 x1 : ffffff80c908c880 x0 : 000000000000002c
[   34.034405] Call trace:
[   34.036841]  gpiochip_get_direction+0x60/0x78 (P)
[   34.041536]  gpiod_get_direction+0x90/0x188
[   34.045710]  gpiolib_seq_show+0x2b4/0x414
[   34.049710]  seq_read_iter+0xe0/0x498
[   34.053362]  seq_read+0xe8/0x128
[   34.056580]  full_proxy_read+0x6c/0xa8
[   34.060320]  vfs_read+0xa4/0x300
[   34.063539]  ksys_read+0x6c/0x104
[   34.066846]  __arm64_sys_read+0x1c/0x28
[   34.070673]  invoke_syscall+0x48/0x10c
[   34.074413]  el0_svc_common.constprop.0+0x40/0xe0
[   34.079106]  do_el0_svc+0x1c/0x28
[   34.082411]  el0_svc+0x34/0x108
[   34.085545]  el0t_64_sync_handler+0xa0/0xe4
[   34.089720]  el0t_64_sync+0x19c/0x1a0
[   34.093373] ---[ end trace 0000000000000000 ]---

with e623c4303ed1 ("gpiolib: sanitize the return value of gpio_chip::get_direction()") you introduced a new helper
which calls WARN_ON if the callback is not defined, and with removing the pre-check this WARN is now printed on
every gpio-controller which does not implement the gpio_chip.get_direction callback.

as you see in my debug (first line) it affects pinctrl_moore driver which contructs the gpiochip callbacks here:

https://elixir.bootlin.com/linux/v7.0-rc6/source/drivers/pinctrl/mediatek/pinctrl-moore.c#L562

please let me know if this is now invalid and need to be fixed in drive, but imho the WARN_ON here is wrong (optional
callback) beause direction of pins is correctly printed like this after the traces:

gpiochip0: 84 GPIOs, parent: platform/1001f000.pinctrl, pinctrl_moore:
 gpio-0   (                    |tx-disable          ) in  lo 
 gpio-1   (                    |mod-def0            ) in  hi IRQ ACTIVE LOW
 gpio-2   (                    |los                 ) in  hi IRQ 
 gpio-12  (                    |cd                  ) in  lo IRQ ACTIVE LOW
 gpio-13  (                    |reset               ) in  hi IRQ ACTIVE LOW
 gpio-14  (                    |WPS                 ) in  hi IRQ ACTIVE LOW
 gpio-21  (                    |tx-disable          ) out hi 
 gpio-63  (                    |pcie-3-hog          ) out hi 
 gpio-69  (                    |mod-def0            ) in  lo IRQ ACTIVE LOW
 gpio-70  (                    |los                 ) in  hi IRQ 
 gpio-79  (                    |pcie-2-hog          ) out hi 
 gpio-82  (                    |PHY reset           ) out hi ACTIVE LOW
 gpio-83  (                    |PHY reset           ) out hi ACTIVE LOW

regards Frank