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

[Simon Glass]

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.

>
> The problem is if gpio_hog_probe_all returns an error, board_init_r will
> hang()
>
> See:
> - https://github.com/u-boot/u-boot/blob/v2022.07/common/board_r.c#L824-L825
> - https://github.com/u-boot/u-boot/blob/v2022.07/common/board_r.c#L763
> -
> https://github.com/u-boot/u-boot/blob/v2022.07/drivers/gpio/gpio-uclass.c#L330-L332
>
> A practical example of how this may occur is when an i2c gpio expander
> (e.g. nxp,pca9534) uses gpio-hog, but the gpio expander is depopulated.
>
> Arguably, the best solution is to use a different device tree when the
> gpio expander is not populated. This patch allows the gpio-hog to fail
> gracefully and continue booting if gpio-hog-optional is used.
>
> 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.

Regards,
Simon