ACK/Cmnt: [SRU] [F/G/Unstable/OEM-5.6] [PATCH 0/3] Enable brightness control on HP DreamColor panel

Stefan Bader stefan.bader at
Thu Oct 8 09:27:01 UTC 2020

On 08.10.20 11:15, Kai-Heng Feng wrote:
>> On Oct 8, 2020, at 17:07, Stefan Bader <stefan.bader at> wrote:
>> On 07.10.20 13:53, Kai-Heng Feng wrote:
>>> BugLink:
>>> [Impact]
>>> Brightness on HP DreamColor panel, which can be found on new HP Zbook
>>> Studio, cannot be changed.
>>> [Fix]
>>> Let DRM know the panel should use DPCD instead of PWM to control
>>> backlight.
>>> [Test]
>>> With the patch applied, we can change the brightness on HP Zbook Studio.
>>> [Regression Potential]
>>> If there's any panel in the quirk list depends on checking brightness
>>> control capability then this change will have an impact. However it's
>>> rather unlikely because it defeats the purpose of the quirk list.
>>> Kai-Heng Feng (2):
>>>  UBUNTU: SAUCE: drm/i915/dpcd_bl: Skip testing control capability with
>>>    force DPCD quirk
>>>  UBUNTU: SAUCE: drm/dp: HP DreamColor panel brigntness fix
>>> Lyude Paul (1):
>>>  drm/i915/dpcd_bl: Unbreak enable_dpcd_backlight modparam
>>> drivers/gpu/drm/drm_dp_helper.c                       | 1 +
>>> drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c | 9 ++++++---
>>> 2 files changed, 7 insertions(+), 3 deletions(-)
>> For Focal I am not really happy to ack because it seems to add a lot of new
>> SAUCE which could mean it is not accepted upstream or is rather new that there
>> was not much baking time. All things that do not really comply with the concept
>> of a stable release.
> I hope users who want to stick to GA kernel can get fixes too.

Yes, of course. This was not so much about the change itself but more about the
timing. I understand this causes more work but I think a staged approach (first
oem and devel and later stable) would be better. In this case it is probably too
simple to be a risk but as you say it might become a different approach upstream
and so we should avoid back and forth.


>> Though the first patch now is upstream:
>> commit d082119f4277ff4a63e44d293864aa9f2112b217
>> Author: Lyude Paul <lyude at>
>> Date:   Mon Apr 13 17:44:06 2020 -0400
>>    drm/i915/dpcd_bl: Unbreak enable_dpcd_backlight modparam
>> So the following should be put before your sign-off when things get committed:
>> (cherry picked from commit d7fb38ae36a2dc97924b075ad1d1a88792777ea9)
>> Signed-off-by: Rodrigo Vivi <rodrigo.vivi at>
>> (cherry picked from commit d082119f4277ff4a63e44d293864aa9f2112b217)
>> Signed-off-by: ...
>> The other two patches, at least they appear harmless enough, are you planning on
>> upstreaming those?
> Yes, and it's under review. Will send another SRU if upstream version is different to this one.
> Kai-Heng
>> For now, as this looks isolated enough...
>> Acked-by: Stefan Bader <stefan.bader at>

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