[PATCH] gpio: uclass: Introduce gpio-hog-optional property

[Nate Drude]

Hi All,

On 9/14/22 9:16 AM, Tom Rini wrote:
> On Wed, Sep 14, 2022 at 08:59:52AM -0500, Nate Drude wrote:
>> Hi Simon,
>>
>> On 9/14/22 7:49 AM, Simon Glass wrote:
>>> Hi Nate,
>>>
>>> On Mon, 12 Sept 2022 at 14:57, Nate Drude <nate.d at variscite.com> wrote:
>>>>
>>>> Hi Simon and Fabio,
>>>>
>>>> On 9/12/22 3:16 PM, Simon Glass wrote:
>>>>> Hi,
>>>>>
>>>>> On Mon, 12 Sept 2022 at 12:48, Fabio Estevam <festevam at gmail.com> wrote:
>>>>>>
>>>>>> Hi Nate and Simon,
>>>>>>
>>>>>> On Mon, Sep 12, 2022 at 2:55 PM Nate Drude <nate.d at variscite.com> wrote:
>>>>>>>
>>>>>>> gpio_hog_probe_all is invoked by init_sequence_r in board_r.c.
>>>>>>> If device_probe fails for any gpio-hog, boot hangs with the following error:
>>>>>>>
>>>>>>>> initcall sequence 00000000fffc8e18 failed at call 000000004023b320 (err=-121)
>>>>>>>> ### ERROR ### Please RESET the board ###
>>>>>>>
>>>>>>> gpio-hog-optional allows the boot sequence to continue if device_probe
>>>>>>> fails for optional gpio-hog(s).
>>>>>>>
>>>>>>> Signed-off-by: Nate Drude <nate.d at variscite.com>
>>>>>>> ---
>>>>>>>     doc/device-tree-bindings/gpio/gpio.txt | 1 +
>>>>>>>     drivers/gpio/gpio-uclass.c             | 4 +++-
>>>>>>>     2 files changed, 4 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/doc/device-tree-bindings/gpio/gpio.txt b/doc/device-tree-bindings/gpio/gpio.txt
>>>>>>> index 1481ed607d..02d296316b 100644
>>>>>>> --- a/doc/device-tree-bindings/gpio/gpio.txt
>>>>>>> +++ b/doc/device-tree-bindings/gpio/gpio.txt
>>>>>>> @@ -189,6 +189,7 @@ gpio-controller's driver probe function.
>>>>>>>     Each GPIO hog definition is represented as a child node of the GPIO controller.
>>>>>>>     Required properties:
>>>>>>>     - gpio-hog:   A property specifying that this child node represents a GPIO hog.
>>>>>>> +- gpio-hog-optional: A property specifying to continue boot when device_probe fails in gpio_hog_probe_all
>>>>>>
>>>>>> gpio-hog-optional property does not exist in Linux.
>>>>>>
>>>>>> If this property is introduced then U-Boot and Linux devicetrees will
>>>>>> not be in sync.
>>>>>>
>>>>>> Can this be fixed differently?
>>>>>
>>>>> Nate, can you send a patch to Linux with the binding update?
>>>>>
>>>>> Regards,
>>>>> Simon
>>>>
>>>> Thanks for your responses and feedback.
>>>>
>>>> I don't think gpio-hog-optional is relevant to Linux.
>>>
>>> Sure, but Linux is (for better or worse) the main repo for the device
>>> tree bindings.
>>
>> I am not understanding the action. I think you're suggesting I update the
>> Linux device tree bindings so they stay aligned with U-Boot, adding a
>> property gpio-hog-optional after this line: https://github.com/torvalds/linux/blob/v6.0-rc5/Documentation/devicetree/bindings/gpio/gpio.txt#L191
>>
>> However, since it's not relevant to Linux, I think it will be confusing
>> since it will have no effect and won't be be used in any Linux code.
>>
>> Can you please advise what description I should use for the
>> gpio-hog-optional property so that the Linux maintainers would accept such a
>> patch?
> 
> Yes, that would be one way to go about this, and there are other
> non-Linux bindings in the Linux kernel tree, but this might be the first
> property of an existing binding, so that might also be a bit challenging
> to get accepted, or find out what the preferred solution is.
> 
> [snip]
>>>> Do you have any suggestions for a better approach? Does it make sense
>>>> for gpio_hog_probe_all to cause a fatal error when the gpio hog probe
>>>> fails (most devices, including the gpio-expander, will not cause a hang
>>>> if they fail to probe)?
>>>
>>> I think your approach is fine as is.
>>
>> An alternate approach is to modify the default behavior so that
>> gpio_hog_probe_all will not trigger a fatal error. Do you think this is
>> better?
> 
> This too would be acceptable.
> 

Thanks for the discussion and feedback. I prefer to avoid changing the 
bindings in Linux if possible.

Would it be acceptable if I rework gpio_hog_probe_all so that it prints 
an error "Failed to probe device..." if any device_probe fails, but 
always returns 0 to avoid a fatal error in board_init_r? I can submit a 
v2 patch, but I want to screen any problems with the approach first.

Thanks,
Nate