Bug 207835

Summary:	ACPI video backlight brightness control does not work on Acer TravelMate 5735Z by default
Product:	ACPI	Reporter:	Paul Menzel (pmenzel+bugzilla.kernel.org)
Component:	Other	Assignee:	acpi_other
Status:	CLOSED CODE_FIX
Severity:	normal	CC:	jwrdegoede, pmenzel+bugzilla.kernel.org, rui.zhang
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	5.6.7	Subsystem:
Regression:	No	Bisected commit-id:
Attachments:	ACPI: video: Use native backlight on Acer TravelMate 5735Z ACPI: video: Use native backlight on Acer TravelMate 5735Z

Description Paul Menzel 2020-05-21 21:01:40 UTC

On the Intel GM45/GMA 4500MHD laptop with Debian Sid/unstable and Linux 5.6.7 and GNOME Shell 3.36.2, trying to change the brightness of the internal display using the function keys, GNOME shows the OSD, which seems to have five levels (from acer_wmi?), but the actual brightness does *not* change. There is only `/sys/class/backlight/intel_backlight/brightness` though, and writing values to it seems to work.

Booting the system with `acpi_backlight=vendor`, exposes `/sys/devices/platform/acer-wmi/backlight/acer-wmi/brightness`, but the behavior is the same.

Booting the system with `acpi_backlight=native` or `acpi_backlight=native`, changing the brightness with the function keys works, and there now seem to be 15 (or 16) levels.

```
$ grep '.*' /sys/class/dmi/id/*_* 2> /dev/null
/sys/class/dmi/id/bios_date:07/26/2011
/sys/class/dmi/id/bios_vendor:Acer
/sys/class/dmi/id/bios_version:V1.14
/sys/class/dmi/id/board_asset_tag:Base Board Asset Tag
/sys/class/dmi/id/board_name:BA51_MV
/sys/class/dmi/id/board_vendor:Acer
/sys/class/dmi/id/board_version:V1.14
/sys/class/dmi/id/chassis_asset_tag:
/sys/class/dmi/id/chassis_type:10
/sys/class/dmi/id/chassis_vendor:Acer
/sys/class/dmi/id/chassis_version:V1.14
/sys/class/dmi/id/product_family:Intel_Mobile
/sys/class/dmi/id/product_name:TravelMate 5735Z
/sys/class/dmi/id/product_sku:Montevina_Fab
/sys/class/dmi/id/product_version:V1.14
/sys/class/dmi/id/sys_vendor:Acer
```

Comment 1 Paul Menzel 2020-05-21 21:26:29 UTC

Created attachment 289201 [details]
ACPI: video: Use native backlight on Acer TravelMate 5735Z

From commit 1c8fbc1f9b (ACPI: video: Use native backlight on Acer Aspire 5783z):

> The Acer Aspire 5783z shipped with Windows 7 and as such does not trigger our
> "win8 ready" heuristic for preferring the native backlight interface.

I do not know about the “win8 ready” heuristic, but this laptop also shipped with Windows 7 (at least it has such a sticker on it). So I attach a similar patch and mention it in the commit message too.

Comment 2 Paul Menzel 2020-05-21 21:30:05 UTC

Created attachment 289203 [details]
ACPI: video: Use native backlight on Acer TravelMate 5735Z

Add bug report URL in a comment.

Comment 3 Hans de Goede 2020-05-22 10:08:44 UTC

Hi Paul,

Thank you for the bug-report and the patch. Can you please submit the patch upstream using the standard Linux kernel patch submission process? :

https://www.kernel.org/doc/html/latest/process/submitting-patches.html

Comment 4 Hans de Goede 2020-05-22 10:12:56 UTC

Note the attached-patch looks fine, you just need to "git send-email" it:

To:
Rafael J. Wysocki" <rjw@rjwysocki.net>
Len Brown <lenb@kernel.org>

Cc:
linux-acpi@vger.kernel.org

And since I've just reviewed it and it looks good to me, you may also add my:

Reviewed-by: Hans de Goede <hdegoede@redhat.com>

Just add that line to the commit message directly above your Signed-off-by before sending out the patch.

Comment 5 Zhang Rui 2020-06-30 06:49:48 UTC

Patch merged in upstream

commit c41c36e900a337b4132b12ccabc97f5578248b44
Author:     Paul Menzel <pmenzel@molgen.mpg.de>
AuthorDate: Fri May 22 14:22:28 2020 +0200
Commit:     Rafael J. Wysocki <rafael.j.wysocki@intel.com>
CommitDate: Mon May 25 11:58:51 2020 +0200

    ACPI: video: Use native backlight on Acer TravelMate 5735Z
    
    Currently, changing the brightness of the internal display of the Acer
    TravelMate 5735Z does not work. Pressing the function keys or changing the
    slider, GNOME Shell 3.36.2 displays the OSD (five steps), but the
    brightness does not change.
    
    The Acer TravelMate 5735Z shipped with Windows 7 and as such does not
    trigger our "win8 ready" heuristic for preferring the native backlight
    interface.
    
    Still ACPI backlight control doesn't work on this model, where as the
    native (intel_video) backlight interface does work by adding
    `acpi_backlight=native` or `acpi_backlight=none` to Linux’ command line.
    
    So, add a quirk to force using native backlight control on this model.
    
    Link: https://bugzilla.kernel.org/show_bug.cgi?id=207835
    Reviewed-by: Hans de Goede <hdegoede@redhat.com>
    Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
    Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>