Nouveau - Oct 2021 - [Intel-gfx] [PATCH v2 0/4] drm/dp, drm/i915: Finish basic PWM support for VESA backlight helpers

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'm more curious if you might happen to
have
any systems that would be able to test this.
> 
> 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(-)
> > 
> 
-- 
Cheers,
 Lyude Paul (she/her)
 Software Engineer at Red Hat

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 at 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(-)
>>>
>>
>