[Intel-gfx] [PATCH] backlight: Don't read back backlight setting from kernel on DPMS off

[Hans de Goede]

Hi,

On 06/05/2014 10:24 PM, Chris Wilson wrote:
> On Thu, Jun 05, 2014 at 09:08:33PM +0200, Hans de Goede wrote:
>> Note that it is read after the framebuffer has been resized and a new mode
>> has been set on "pipe 0 using LVDS1", could this perhaps cause the 0 to be
>> read when using actual_brightness ?
> 
> Indeed, that is likely the explanation, and shows the fallacy in the
> current approach. And also explains why acpi_backlight works with the
> current code, but that the kernel interfering with intel_backlight does
> not.
>  
>> Also I've just had a user who has been testing this patch come back to
>> me it does help, but he still has a suspend/resume issue. It seems that
>> some X app / gnome-component is doing the following:
>>
>> 1) DPMS off
>> 2) Read backlight xrandr property -> this will now return 0
>> 3) Set backlight xrandr property value to the value just read, aka 0
>> 4) DPMS on -> "restores" backlight to 0 because of the property set
>>
>> I believe the best way to fix this will be to make
>> xxx_output_get_property("backlight") return backlight_active_level
>> when in DPMS off, rather then calling xxx_output_backlight_get.
> 
> I had the same thought when reviewing the code following your email. I
> modified sna, but I think I want to restructure how backlight is saved
> around modesets.

And now a mail with the promised patch really attached ...

Regards,

Hans

-------------- next part --------------
A non-text attachment was scrubbed...
Name: 0001-backlight-Don-t-read-back-backlight-setting-from-ker.patch
Type: text/x-patch
Size: 3168 bytes
Desc: not available
URL: <http://lists.freedesktop.org/archives/intel-gfx/attachments/20140606/c36c0516/attachment.bin>