linux-kernel - Re: [PATCH v3 4/4] gpio: Hide valid

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Message-ID: <CAD=FV=Vg8_ZOLgLoC4WhFPzhVsxXFC19NrF38W6cW_W_3nFjbw@mail.gmail.com>
Date: Sat, 12 Apr 2025 16:00:20 -0700
From: Doug Anderson <dianders@...omium.org>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>, 
	Linus Walleij <linus.walleij@...aro.org>, Bartosz Golaszewski <brgl@...ev.pl>, linux-gpio@...r.kernel.org, 
	linux-kernel@...r.kernel.org, Biju Das <biju.das.jz@...renesas.com>, 
	Geert Uytterhoeven <geert@...ux-m68k.org>, linux-arm-msm <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v3 4/4] gpio: Hide valid_mask from direct assignments

Hi,

On Wed, Mar 5, 2025 at 5:23 AM Matti Vaittinen <mazziesaccount@...il.com> wrote:
>
> The valid_mask member of the struct gpio_chip is unconditionally written
> by the GPIO core at driver registration. Current documentation does not
> mention this but just says the valid_mask is used if it's not NULL. This
> lured me to try populating it directly in the GPIO driver probe instead
> of using the init_valid_mask() callback. It took some retries with
> different bitmaps and eventually a bit of code-reading to understand why
> the valid_mask was not obeyed. I could've avoided this trial and error if
> the valid_mask was hidden in the struct gpio_device instead of being a
> visible member of the struct gpio_chip.
>
> Help the next developer who decides to directly populate the valid_mask
> in struct gpio_chip by hiding the valid_mask in struct gpio_device and
> keep it internal to the GPIO core.
>
> Suggested-by: Linus Walleij <linus.walleij@...aro.org>
> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> Reviewed-by: Linus Walleij <linus.walleij@...aro.org>
> ---
> Revision history:
> v2 => v3:
>  - Rebase to gpio/for-next
> v1 => v2:
>  - Hide the valid_mask instead of documenting it as internal to GPIO
>    core as suggested by Linus W.
> https://lore.kernel.org/all/Z71qphikHPGB0Yuv@mva-rohm/
> ---
>  drivers/gpio/gpiolib.c      | 16 ++++++++--------
>  drivers/gpio/gpiolib.h      |  3 +++
>  include/linux/gpio/driver.h |  8 --------
>  3 files changed, 11 insertions(+), 16 deletions(-)

FWIW, I've found that this patch is crashing me at bootup on my
sc7180-trogdor board. The problem is pretty obvious in gdb.
"gc->gpiodev" is NULL in gpiochip_line_is_valid().

0xffff80008066c760 in gpiochip_line_is_valid (gc=0xffff000083223890,
offset=offset@...ry=66) at drivers/gpio/gpiolib.c:746
746             if (likely(!gc->gpiodev->valid_mask))
(gdb) bt
#0  0xffff80008066c760 in gpiochip_line_is_valid
(gc=0xffff000083223890, offset=offset@...ry=66) at
drivers/gpio/gpiolib.c:746
#1  0xffff800080666338 in msm_pinmux_request (pctldev=<optimized out>,
offset=66) at drivers/pinctrl/qcom/pinctrl-msm.c:152
#2  0xffff800080662314 in pin_request (pctldev=0xffff000082686ac0,
pin=66, owner=0xffff000082c02790 "3500000.pinctrl", gpio_range=0x0)
    at drivers/pinctrl/pinmux.c:176
#3  0xffff800080662900 in pinmux_enable_setting
(setting=0xffff000082684b40) at drivers/pinctrl/pinmux.c:445
#4  0xffff80008065fd54 in pinctrl_commit_state (p=0xffff000083a07520,
state=0xffff000082684a40) at drivers/pinctrl/core.c:1300
#5  0xffff8000806605bc in pinctrl_select_state (p=0xffff000083223890,
p@...ry=0xffff000082686ac0, state=0x42) at drivers/pinctrl/core.c:1381
#6  pinctrl_claim_hogs (pctldev=0xffff000082686ac0) at
drivers/pinctrl/core.c:2136
#7  pinctrl_enable (pctldev=0xffff000082686ac0) at drivers/pinctrl/core.c:2156
#8  0xffff800080660814 in pinctrl_register
(pctldesc=0xffff000083223a90, dev=0xffff000081406410,
driver_data=0xffff000083223880) at drivers/pinctrl/core.c:2193
#9  0xffff800080660df4 in devm_pinctrl_register
(dev=0xffff000081406410, pctldesc=0xffff000083223a90,
driver_data=0xffff000083223880) at drivers/pinctrl/core.c:2313
#10 0xffff8000806657b4 in msm_pinctrl_probe (pdev=0xffff000081406400,
soc_data=<optimized out>) at drivers/pinctrl/qcom/pinctrl-msm.c:1579
#11 0xffff80008066afcc in sc7180_pinctrl_probe
(pdev=0xffff000083223890) at
drivers/pinctrl/qcom/pinctrl-sc7180.c:1147
#12 0xffff80008089583c in platform_probe (_dev=0xffff000081406410) at
drivers/base/platform.c:1404

(gdb) print gc->gpiodev
$1 = (struct gpio_device *) 0x0

-Doug