Re: [PATCH 2/2] platform/surface: surfacepro3_button: don't load on amd variant

[Hans de Goede <hdegoede@redhat.com>]

Hi Sachi,

On 11/9/21 09:11, Sachi King wrote:
> The AMD variant of the Surface Laptop report 0 for their OEM platform
> revision.  The Surface devices that require the surfacepro3_button
> driver do not have the _DSM that gets the OEM platform revision.  If the
> method does not exist, load surfacepro3_button.
> 
> Fixes: 64dd243d7356 ("platform/x86: surfacepro3_button: Fix device check")
> Co-developed-by: Maximilian Luz <luzmaximilian@gmail.com>
> Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
> Signed-off-by: Sachi King <nakato@nakato.io>

Thank you for your patch.

I'm afraid that I do not entirely understand the problem and thus
I also cannot review this patch properly.

Can you please send a new version with a more complete commit message,
explaining things like:

1. On which models this driver currently loads
2. On which models where it loads it should not load
3. The presence / lack of the OEM platform revision _DSM and the
   returned value by the _DSM if present on each of the models on
   which this driver currently loads.

Also I'm wondering, since this is only used on a few
systems, if it would not be better to just use
a dmi_system_id table with a list of systems on which this
should actually load, and also use that list to set the
modalias (using MODULE_DEVICE_TABLE(dmi, ...) ?

That will avoid this module auto-loading at all on devices
where it is not necessary thus speeding up booting a bit
and also not wasting memory by having an unused module sit
in memory.

Note the driver can still bind by the ACPI ids, that is fine
you would just:

1. Add a DMI table + MODULE_DEVICE_TABLE(dmi, ...)
2. Add a DMI check to surface_button_check_MSHW0040()
3. Drop MODULE_DEVICE_TABLE(acpi, surface_button_device_ids);

And then presto, the module will not even load on devices
where it should not be used.

###

2 more requests related to this patch

1. If for the next version you stick with the _DSM presence check
   approach please also add some documentation inside the driver
   in the form of a more elaborate comment.

2. I see this is part of a series for the next version please
   Cc platform-driver-x86@vger.kernel.org for the entire series.

Regards,

Hans



> ---
>  drivers/platform/surface/surfacepro3_button.c | 30 ++++---------------
>  1 file changed, 6 insertions(+), 24 deletions(-)
> 
> diff --git a/drivers/platform/surface/surfacepro3_button.c b/drivers/platform/surface/surfacepro3_button.c
> index 242fb690dcaf..30eea54dbb47 100644
> --- a/drivers/platform/surface/surfacepro3_button.c
> +++ b/drivers/platform/surface/surfacepro3_button.c
> @@ -149,7 +149,8 @@ static int surface_button_resume(struct device *dev)
>  /*
>   * Surface Pro 4 and Surface Book 2 / Surface Pro 2017 use the same device
>   * ID (MSHW0040) for the power/volume buttons. Make sure this is the right
> - * device by checking for the _DSM method and OEM Platform Revision.
> + * device by checking for the _DSM method and OEM Platform Revision DSM
> + * function.
>   *
>   * Returns true if the driver should bind to this device, i.e. the device is
>   * either MSWH0028 (Pro 3) or MSHW0040 on a Pro 4 or Book 1.
> @@ -157,30 +158,11 @@ static int surface_button_resume(struct device *dev)
>  static bool surface_button_check_MSHW0040(struct acpi_device *dev)
>  {
>  	acpi_handle handle = dev->handle;
> -	union acpi_object *result;
> -	u64 oem_platform_rev = 0;	// valid revisions are nonzero
> -
> -	// get OEM platform revision
> -	result = acpi_evaluate_dsm_typed(handle, &MSHW0040_DSM_UUID,
> -					 MSHW0040_DSM_REVISION,
> -					 MSHW0040_DSM_GET_OMPR,
> -					 NULL, ACPI_TYPE_INTEGER);
> -
> -	/*
> -	 * If evaluating the _DSM fails, the method is not present. This means
> -	 * that we have either MSHW0028 or MSHW0040 on Pro 4 or Book 1, so we
> -	 * should use this driver. We use revision 0 indicating it is
> -	 * unavailable.
> -	 */
> -
> -	if (result) {
> -		oem_platform_rev = result->integer.value;
> -		ACPI_FREE(result);
> -	}
> -
> -	dev_dbg(&dev->dev, "OEM Platform Revision %llu\n", oem_platform_rev);
>  
> -	return oem_platform_rev == 0;
> +	// make sure that OEM platform revision DSM call does not exist
> +	return !acpi_check_dsm(handle, &MSHW0040_DSM_UUID,
> +			       MSHW0040_DSM_REVISION,
> +			       BIT(MSHW0040_DSM_GET_OMPR));
>  }
>  
>  
>