Re: [PATCH AUTOSEL 4.19 06/10] ACPI: video: Change disable_backlight_sysfs_if quirks to acpi_backlight=native

[Sasha Levin]

On Mon, Oct 10, 2022 at 09:36:53AM +0200, Hans de Goede wrote:
> Hi,
>
> On 10/10/22 01:57, Sasha Levin wrote:
> > From: Hans de Goede <hdegoede@xxxxxxxxxx>
> >
> > [ Upstream commit c5b94f5b7819348c59f9949b2b75c341a114cdd4 ]
> >
> > Some Toshibas have a broken acpi-video interface for brightness control
> > and need a special firmware call on resume to turn the panel back on.
> > So far these have been using the disable_backlight_sysfs_if workaround
> > to deal with this.
> >
> > The recent x86/acpi backlight refactoring has broken this workaround:
> > 1. This workaround relies on acpi_video_get_backlight_type() returning
> >    acpi_video so that the acpi_video code actually runs; and
> > 2. this relies on the actual native GPU driver to offer the sysfs
> >    backlight interface to userspace.
> >
> > After the refactor this breaks since the native driver will no
> > longer register its backlight-device if acpi_video_get_backlight_type()
> > does not return native and making it return native breaks 1.
> >
> > Keeping the acpi_video backlight handling on resume active, while not
> > using it to set the brightness, is necessary because it does a _BCM
> > call on resume which is necessary to turn the panel back on on resume.
> >
> > Looking at the DSDT shows that this _BCM call results in a Toshiba
> > HCI_SET HCI_LCD_BRIGHTNESS call, which turns the panel back on.
> >
> > This kind of special vendor specific handling really belongs in
> > the vendor specific acpi driver. An earlier patch in this series
> > modifies toshiba_acpi to make the necessary HCI_SET call on resume
> > on affected models.
> >
> > With toshiba_acpi taking care of the HCI_SET call on resume,
> > the acpi_video code no longer needs to call _BCM on resume.
> >
> > So instead of using the (now broken) disable_backlight_sysfs_if
> > workaround, simply setting acpi_backlight=native to disable
> > the broken apci-video interface is sufficient fix things now.
> >
> > After this there are no more users of the disable_backlight_sysfs_if
> > flag and as discussed above the flag also no longer works as intended,
> > so remove the disable_backlight_sysfs_if flag entirely.
> >
> > Acked-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> > Tested-by: Arvid Norlander <lkml@xxxxxxxxx>
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
>
> This patch goes hand in hand with:
>
> commit 3cb1f40dfdc3 ("drivers/platform: toshiba_acpi: Call HCI_PANEL_POWER_ON on resume on some models")
>
> and without that commit also being present it will cause a regression on
> the quirked Toshiba models.
>
> This really is part of the big x86/ACPI backlight handling refactor which
> has landed in 6.1 and as such is not intended for older kernels, please
> drop this from the stable series.

Will do, thanks!

--
Thanks,
Sasha