Re: [Nouveau] [Intel-gfx] [PATCH v2 0/4] drm/dp, drm/i915: Finish basic PWM support for VESA backlight helpers

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 10/5/21 10:26 PM, Lyude Paul wrote:
> On Sat, 2021-10-02 at 11:14 +0200, Hans de Goede wrote:
>> Hi Lyude,
>>
>> On 10/2/21 12:53 AM, Lyude Paul wrote:
>>> When I originally moved all of the VESA backlight code in i915 into DRM
>>> helpers, one of the things I didn't have the hardware or time for
>>> testing was machines that used a combination of PWM and DPCD in order to
>>> control their backlights. This has since then caused some breakages and
>>> resulted in us disabling DPCD backlight support on such machines. This
>>> works fine, unless you have a machine that actually needs this
>>> functionality for backlight controls to work at all. Additionally, we
>>> will need to support PWM for when we start adding support for VESA's
>>> product (as in the product of multiplication) control mode for better
>>> brightness ranges.
>>>
>>> So - let's finally finish up implementing basic support for these types
>>> of backlights to solve these problems in our DP helpers, along with
>>> implementing support for this in i915. And since digging into this issue
>>> solved the last questions we really had about probing backlights in i915
>>> for the most part, let's update some of the comments around that as
>>> well!
>>
>> Backlight control is a topic which I'm reasonably familiar with,
>> do you want me to review this series for you ?
> 
> Possibly, although I definitely want to make sure that someone from Intel gets
> a chance to review this as well.

I already expected you would also want someone from Intel to take a look
as well :)

So to figure out if I have system to test this I ended up taking a close
look at the code, which was a nice learning experience. Interesting how
some panels use a combination of DCPD + pwm/gpio for enable/disable and/or
pwm for brightness level control.

I wonder though what DCPD still does if pwm is used for both the
enable/disable and brightness-level control ?

Since I was taking a close look already I decided to do turn this into
a full, the entire set looks good to me:

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

> I'm more curious if you might happen to have
> any systems that would be able to test this.

I don't believe I have a system where I can test this, The only systems
which I have which presumably (I did not check) use eDP / DCPD backlight
control are boring ThinkPads with only i915 gfx.

Regards,

Hans



>>> Changes:
>>> * Fixup docs
>>> * Add patch to stop us from breaking nouveau
>>>
>>> Lyude Paul (4):
>>>   drm/i915: Add support for panels with VESA backlights with PWM
>>>     enable/disable
>>>   drm/nouveau/kms/nv50-: Explicitly check DPCD backlights for aux
>>>     enable/brightness
>>>   drm/dp, drm/i915: Add support for VESA backlights using PWM for
>>>     brightness control
>>>   drm/i915: Clarify probing order in intel_dp_aux_init_backlight_funcs()
>>>
>>>  drivers/gpu/drm/drm_dp_helper.c               | 75 +++++++++++------
>>>  .../drm/i915/display/intel_dp_aux_backlight.c | 80 ++++++++++++++-----
>>>  drivers/gpu/drm/nouveau/nouveau_backlight.c   |  5 +-
>>>  include/drm/drm_dp_helper.h                   |  7 +-
>>>  4 files changed, 122 insertions(+), 45 deletions(-)
>>>
>>
>