Re: [PATCH v1] thermal: core: Do not fail cdev registration because of invalid initial state

Rafael J. Wysocki
2024-06-06T13:43:11Z

On Thu, Jun 6, 2024 at 3:07 PM Daniel Lezcano <daniel.lezcano@linaro.org> wrote:
>
> On 05/06/2024 21:17, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> >
> > It is reported that commit 31a0fa0019b0 ("thermal/debugfs: Pass cooling
> > device state to thermal_debug_cdev_add()") causes the ACPI fan driver
> > to fail probing on some systems which turns out to be due to the _FST
> > control method returning an invalid value until _FSL is first evaluated
> > for the given fan. If this happens, the .get_cur_state() cooling device
> > callback returns an error and __thermal_cooling_device_register() fails
> > as uses that callback after commit 31a0fa0019b0.
> >
> > Arguably, _FST should not return an inavlid value even if it is
> > evaluated before _FSL, so this may be regarded as a platform firmware
> > issue, but at the same time it is not a good enough reason for failing
> > the cooling device registration where the initial cooling device state
> > is only needed to initialize a thermal debug facility.
> >
> > Accordingly, modify __thermal_cooling_device_register() to pass a
> > negative state value to thermal_debug_cdev_add() instead of failing
> > if the initial .get_cur_state() callback invocation fails and adjust
> > the thermal debug code to ignore negative cooling device state values.
> >
> > Fixes: 31a0fa0019b0 ("thermal/debugfs: Pass cooling device state to thermal_debug_cdev_add()")
> > Closes: https://lore.kernel.org/linux-acpi/20240530153727.843378-1-laura.nao@collabora.com
> > Reported-by: Laura Nao <laura.nao@collabora.com>
> > Tested-by: Laura Nao <laura.nao@collabora.com>
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> As it is a driver issue, it should be fixed in the driver, not in the
> core code. The resulting code logic in the core is trying to deal with
> bad driver behavior, it does not really seem appropriate.
>
> The core code has been clean up from the high friction it had with the
> legacy ACPI code. It would be nice to continue it this direction.

Essentially, you are saying that .get_cur_state() should not return an
error even if it gets an utterly invalid value from the platform
firmware.

What value should it return then?