Re: [PATCH] ACPI: video: Add backlight=native DMI quirk for Dell G15 5515

[Daniel Dadap <ddadap@nvidia.com>]

On Mon, Oct 31, 2022 at 09:51:55PM +0000, Limonciello, Mario wrote:
> [Public]
> 
> > -----Original Message-----
> > From: Hans de Goede <hdegoede@redhat.com>
> > Sent: Monday, October 31, 2022 16:26
> > To: Rafael J . Wysocki <rafael@kernel.org>
> > Cc: Hans de Goede <hdegoede@redhat.com>; Len Brown
> > <lenb@kernel.org>; linux-acpi@vger.kernel.org; platform-driver-
> > x86@vger.kernel.org; Daniel Dadap <ddadap@nvidia.com>
> > Subject: [PATCH] ACPI: video: Add backlight=native DMI quirk for Dell G15
> > 5515
> > 
> > The Dell G15 5515 has the WMI interface (and WMI call returns) expected
> > by the nvidia-wmi-ec-backlight interface. But the backlight class device
> > registered by the nvidia-wmi-ec-backlight driver does not actually work.
> > 
> 
> Is there a way to detect this from nvidia-wmi-ec-backlight?  I would think it's
> cleaner to have that driver return -ENODEV so you end up with just the "working"
> amdgpu_bl0.

That would be ideal, although I'm not certain whether this would work
with the new backlight control type selection model where video.ko
determines what type of backlight interface the system is supposed to
have. I am assuming that the below patch is against a kernel predating
the recent changes that Hans made to rework the backlight subsystem,
because IIUC it shouldn't be possible for both the EC backlight driver
and the iGPU's native one to both be active at the same time. I would
expect that without this patch, there would be no working backlight
interfaces on this system when running a newer kernel, since
__acpi_video_get_backlight_type() would return
acpi_backlight_nvidia_wmi_ec, which means
acpi_video_backlight_use_native() would return false, and the iGPU
native driver should not be registering a brightness handler.
 
> > The amdgpu_bl0 native GPU backlight class device does actually work,
> > add a backlight=native DMI quirk for this.
> > 
> > Cc: Daniel Dadap <ddadap@nvidia.com>
> > Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> > ---
> >  drivers/acpi/video_detect.c | 10 ++++++++++
> >  1 file changed, 10 insertions(+)
> > 
> > diff --git a/drivers/acpi/video_detect.c b/drivers/acpi/video_detect.c
> > index 841f6213b4de..88acc09773bb 100644
> > --- a/drivers/acpi/video_detect.c
> > +++ b/drivers/acpi/video_detect.c
> > @@ -645,6 +645,16 @@ static const struct dmi_system_id
> > video_detect_dmi_table[] = {
> >  		},
> >  	},
> > 
> > +	/* Models which have nvidia-ec-wmi support, but should not use it.
> > */
> > +	{
> > +	 .callback = video_detect_force_native,
> > +	 /* Dell G15 5515 */
> > +	 .matches = {
> > +		DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
> > +		DMI_MATCH(DMI_PRODUCT_NAME, "Dell G15 5515"),
> > +		},
> > +	},
> > +
> >  	/*
> >  	 * Desktops which falsely report a backlight and which our heuristics
> >  	 * for this do not catch.
> > --
> > 2.37.3