linux-kernel - RE: [PATCH 2/2] drm/i915/backlight: Add get brightness support of DPCD via AUX

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Message-ID: <DM3PPF208195D8DA16C685D9A84D20FFDB8E31EA@DM3PPF208195D8D.namprd11.prod.outlook.com>
Date: Fri, 26 Sep 2025 09:56:57 +0000
From: "Kandpal, Suraj" <suraj.kandpal@...el.com>
To: "Aaron, Ma" <aaron.ma@...onical.com>
CC: "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	"intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"maarten.lankhorst@...ux.intel.com" <maarten.lankhorst@...ux.intel.com>,
	"mripard@...nel.org" <mripard@...nel.org>, "tzimmermann@...e.de"
	<tzimmermann@...e.de>, "airlied@...il.com" <airlied@...il.com>,
	"simona@...ll.ch" <simona@...ll.ch>, "jani.nikula@...ux.intel.com"
	<jani.nikula@...ux.intel.com>, "Vivi, Rodrigo" <rodrigo.vivi@...el.com>,
	"Deak, Imre" <imre.deak@...el.com>, "joonas.lahtinen@...ux.intel.com"
	<joonas.lahtinen@...ux.intel.com>
Subject: RE: [PATCH 2/2] drm/i915/backlight: Add get brightness support of
 DPCD via AUX



> -----Original Message-----
> From: Aaron Ma <aaron.ma@...onical.com>
> Sent: Friday, September 26, 2025 3:23 PM
> To: Kandpal, Suraj <suraj.kandpal@...el.com>
> Cc: dri-devel@...ts.freedesktop.org; intel-gfx@...ts.freedesktop.org; linux-
> kernel@...r.kernel.org; maarten.lankhorst@...ux.intel.com;
> mripard@...nel.org; tzimmermann@...e.de; airlied@...il.com;
> simona@...ll.ch; jani.nikula@...ux.intel.com; Vivi, Rodrigo
> <rodrigo.vivi@...el.com>; Deak, Imre <imre.deak@...el.com>;
> joonas.lahtinen@...ux.intel.com
> Subject: Re: [PATCH 2/2] drm/i915/backlight: Add get brightness support of
> DPCD via AUX
> 
> On Fri, Sep 26, 2025 at 5:26 PM Kandpal, Suraj <suraj.kandpal@...el.com>
> wrote:
> >
> > > Subject: [PATCH 2/2] drm/i915/backlight: Add get brightness support
> > > of DPCD via AUX
> > >
> > > Use drm common helper to read brightness from both luminance and AUX
> > > mode to support get_brightness from DPCD via AUX.
> > >
> > > Signed-off-by: Aaron Ma <aaron.ma@...onical.com>
> > > ---
> > >  .../drm/i915/display/intel_dp_aux_backlight.c | 20
> > > ++++++-------------
> > >  1 file changed, 6 insertions(+), 14 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > index 0a3a3f6a5f9d8..0ee6fd0f41ef0 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c
> > > @@ -454,24 +454,16 @@ static u32
> > > intel_dp_aux_vesa_get_backlight(struct
> > > intel_connector *connector, en  {
> > >       struct intel_dp *intel_dp = enc_to_intel_dp(connector->encoder);
> > >       struct intel_panel *panel = &connector->panel;
> > > -     u8 buf[3];
> > > -     u32 val = 0;
> > > -     int ret;
> > >
> > > -     if (panel->backlight.edp.vesa.luminance_control_support) {
> > > -             ret = drm_dp_dpcd_read(&intel_dp->aux,
> > > DP_EDP_PANEL_TARGET_LUMINANCE_VALUE, buf,
> > > -                                    sizeof(buf));
> > > -             if (ret < 0) {
> > > -                     drm_err(intel_dp->aux.drm_dev,
> > > -                             "[CONNECTOR:%d:%s] Failed to read
> > > Luminance from DPCD\n",
> > > -                             connector->base.base.id, connector-
> > > >base.name);
> > > -                     return 0;
> > > -             }
> > > +     if (!panel->backlight.edp.vesa.info.aux_set) {
> > > +             u32 pwm_level =
> > > + panel->backlight.pwm_funcs->get(connector,
> > > unused);
> > >
> > > -             val |= buf[0] | buf[1] << 8 | buf[2] << 16;
> > > -             return val / 1000;
> > > +             return intel_backlight_level_from_pwm(connector,
> > > pwm_level);
> > >       }
> > >
> > > +     connector->panel.backlight.level =
> > > +             drm_edp_backlight_get_level(&intel_dp->aux,
> > > +&panel->backlight.edp.vesa.info);
> > > +
> >
> > Just call the intel_dp_aux_vesa_get_backlight here and call the
> > drm_edp_backlight get level in there
> >
> 
> Do you mean no call of  pwm get?
> 
> I thought it should be aligned with set_level when aux_set == 0.

I misunderstood the code here its as it should be the diff just made it seem weird

Regards,
Suraj Kandpal

> 
> Thanks,
> Aaron
> 
> > Regards,
> > Suraj Kandpal
> >
> >
> > >       return connector->panel.backlight.level;  }
> > >
> > > --
> > > 2.43.0
> >