Message-ID: <5add8ddd-fcc8-445d-9699-42c27df0e1c7@gmail.com>
Date: Sun, 13 Apr 2025 11:51:29 +0300
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Doug Anderson <dianders@...omium.org>
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>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Bjorn Andersson <andersson@...nel.org>
Subject: Re: [PATCH v3 4/4] gpio: Hide valid_mask from direct assignments

On 13/04/2025 11:08, Matti Vaittinen wrote:
> Hi Doug,
> 
> On 13/04/2025 02:00, Doug Anderson wrote:
>> 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().
> 
> Thanks for debugging this! I find this odd. It seems to me the pinctrl- 
> msm.c is calling the gpiochip_add_data() for the chip, in the 
> msm_gpio_init() - which is called from the msm_pinctrl_probe().
> 
> The gpiochip_add_data() should go to the gpiochip_add_data_with_key() - 
> where the gpiodev should be allocated and set.
> 
> I don't spot any successful code path where the gpiodev was not allocated.
> 
>>
>> 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>,
> 
> Ah, but now I see the call comes from the pinmux. Looking at the 
> msm_pinctrl_probe() - the pincontroller is registered before the gpio. 
> Maybe, with unlucky timing, the request happens right after registering 
> the pinctrl - but before registering the gpios.
> 
> This, I think, can be a bug even before this change (because the 
> valid_mask is not initialized prior the gpio registration) - but this 
> change now made it obvious.
> 
> I see the probe is actually an exported function, and there are mentions 
> about ACPI support etc. I don't really know if there are valid cases 
> where the pincontroller should be usable without the gpiochip. If this 
> is the case, the unconditional call to the gpiochip_line_is_valid() from 
> the msm_pinmux_request() smells wrong.
> 
> I am not sure about the right fix. One could try:
> 
> @@ -1568,6 +1568,10 @@ int msm_pinctrl_probe(struct platform_device *pdev,
>          if (pctrl->irq < 0)
>                  return pctrl->irq;
> 
> +       ret = msm_gpio_init(pctrl);
> +       if (ret)
> +               return ret;
> +
>          pctrl->desc.owner = THIS_MODULE;
>          pctrl->desc.pctlops = &msm_pinctrl_ops;
>          pctrl->desc.pmxops = &msm_pinmux_ops;
> @@ -1582,10 +1586,6 @@ int msm_pinctrl_probe(struct platform_device *pdev,
>                  return PTR_ERR(pctrl->pctrl);
>          }
> 
> -       ret = msm_gpio_init(pctrl);
> -       if (ret)
> -               return ret;
> -
>          platform_set_drvdata(pdev, pctrl);
> 
>          dev_dbg(&pdev->dev, "Probed Qualcomm pinctrl driver\n")
> 
> but I am not at all this is the fix we're looking after. I wonder if 
> Krzysztof has any suggestions? (Seeing he has been authoring some 
> changes here :] )
> 

+Björn

> Yours,
>      -- Matti
> 
> 
>> 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
> 

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