Re: [PATCH 1/3] spi: tegra210-quad: use device_reset_optional() instead of device_reset()

[Breno Leitao]

Hello Arnd, Thierry, Jonathan, Sowjanya,

On Tue, Mar 18, 2025 at 09:07:28PM +0100, Arnd Bergmann wrote:
> On Tue, Mar 18, 2025, at 20:13, Mark Brown wrote:
> > On Tue, Mar 18, 2025 at 08:00:05PM +0100, Arnd Bergmann wrote:
> >
> >> That does sound like the easiest answer: if the spi controller driver
> >> knows that it needs a reset but there is no reset controller, shutting
> >> itself down and removing its child devices seems like the least
> >> offensive action.
> >
> > In that case it's probably more just refuse to probe in the first case
> > without the reset controller.  Given that the device isn't working at
> > all it seems like the hardware description is broken anyway...
> 
> Right, I see now that it's doing a rather silly
> 
>        if (device_reset(tqspi->dev) < 0)
>                dev_warn_once(tqspi->dev, "device reset failed\n");
> 
> after which it just continues instead of propagating returning
> the error from the probe function. 

This would be another option, and I would be happy to update this patch
with this suggestion.

This patch was attempting to address the issue the other way around,
where I was expecting that the reset methods are optional, thus
marking the device_reset() function as optional.

It appears that on certain UEFI machine types, the ACPI firmware doesn't
implement the _RST methods, and device_reset() will *always* fail. It's
unclear whether this is due to a broken ACPI table or if it was
intentionally designed this way.

Tagging the driver maintainer (Thierry, Jonathan, Sowjanya) who might
have a better understanding of the design in such cases.

> This is also broken when
> the reset controller driver has not been loaded yet and it
> should do an -EPROBE_DEFER.
> 
> In case of a broken ACPI table, this would simply fail the
> probe() with an error, which seems like a sensible behavior.

Do we agree that the device reset methods MUST always exist (on both DT
and UEFI hosts)?

Anyway, from my naive view, we should:

1) Mark as required, and fail the probe,  if this device_reset() must
   have available methods. (Arnd's suggestion)

2) Mark device_reset as optional if device reset is optional (as the
   current situation suggest).  

   a) If the requirements are different for DT and UEFI, then should we 
      create a "device_reset_optional_on_acpi_but_not_DT()" helper to
      handle such cases(!?)

Thanks for the discussion,
--breno