[PATCH v2] drm/amd/display: Reduce HDMI pixel encoding if max clock is exceeded

[Alex Deucher]

On Fri, Dec 20, 2019 at 10:10 AM Tom Anderson <thomasanderson at google.com> wrote:
>
> Ping.  Is there any action required to get this landed?

Looks good to me, but I'd like to hear from the display guys.

Alex


>
> On Tue, Dec 10, 2019 at 10:59:24AM -0800, Tom Anderson wrote:
> > Friendly ping.
> >
> > On Mon, Dec 02, 2019 at 01:47:13PM -0800, Thomas Anderson wrote:
> > > For high-res (8K) or HFR (4K120) displays, using uncompressed pixel
> > > formats like YCbCr444 would exceed the bandwidth of HDMI 2.0, so the
> > > "interesting" modes would be disabled, leaving only low-res or low
> > > framerate modes.
> > >
> > > This change lowers the pixel encoding to 4:2:2 or 4:2:0 if the max TMDS
> > > clock is exceeded. Verified that 8K30 and 4K120 are now available and
> > > working with a Samsung Q900R over an HDMI 2.0b link from a Radeon 5700.
> > >
> > > Signed-off-by: Thomas Anderson <thomasanderson at google.com>
> > > ---
> > >  .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 45 ++++++++++---------
> > >  1 file changed, 23 insertions(+), 22 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > index 7aac9568d3be..803e59d97411 100644
> > > --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
> > > @@ -3356,27 +3356,21 @@ get_output_color_space(const struct dc_crtc_timing *dc_crtc_timing)
> > >     return color_space;
> > >  }
> > >
> > > -static void reduce_mode_colour_depth(struct dc_crtc_timing *timing_out)
> > > -{
> > > -   if (timing_out->display_color_depth <= COLOR_DEPTH_888)
> > > -           return;
> > > -
> > > -   timing_out->display_color_depth--;
> > > -}
> > > -
> > > -static void adjust_colour_depth_from_display_info(struct dc_crtc_timing *timing_out,
> > > -                                           const struct drm_display_info *info)
> > > +static bool adjust_colour_depth_from_display_info(
> > > +   struct dc_crtc_timing *timing_out,
> > > +   const struct drm_display_info *info)
> > >  {
> > > +   enum dc_color_depth depth = timing_out->display_color_depth;
> > >     int normalized_clk;
> > > -   if (timing_out->display_color_depth <= COLOR_DEPTH_888)
> > > -           return;
> > >     do {
> > >             normalized_clk = timing_out->pix_clk_100hz / 10;
> > >             /* YCbCr 4:2:0 requires additional adjustment of 1/2 */
> > >             if (timing_out->pixel_encoding == PIXEL_ENCODING_YCBCR420)
> > >                     normalized_clk /= 2;
> > >             /* Adjusting pix clock following on HDMI spec based on colour depth */
> > > -           switch (timing_out->display_color_depth) {
> > > +           switch (depth) {
> > > +           case COLOR_DEPTH_888:
> > > +                   break;
> > >             case COLOR_DEPTH_101010:
> > >                     normalized_clk = (normalized_clk * 30) / 24;
> > >                     break;
> > > @@ -3387,14 +3381,15 @@ static void adjust_colour_depth_from_display_info(struct dc_crtc_timing *timing_
> > >                     normalized_clk = (normalized_clk * 48) / 24;
> > >                     break;
> > >             default:
> > > -                   return;
> > > +                   /* The above depths are the only ones valid for HDMI. */
> > > +                   return false;
> > >             }
> > > -           if (normalized_clk <= info->max_tmds_clock)
> > > -                   return;
> > > -           reduce_mode_colour_depth(timing_out);
> > > -
> > > -   } while (timing_out->display_color_depth > COLOR_DEPTH_888);
> > > -
> > > +           if (normalized_clk <= info->max_tmds_clock) {
> > > +                   timing_out->display_color_depth = depth;
> > > +                   return true;
> > > +           }
> > > +   } while (--depth > COLOR_DEPTH_666);
> > > +   return false;
> > >  }
> > >
> > >  static void fill_stream_properties_from_drm_display_mode(
> > > @@ -3474,8 +3469,14 @@ static void fill_stream_properties_from_drm_display_mode(
> > >
> > >     stream->out_transfer_func->type = TF_TYPE_PREDEFINED;
> > >     stream->out_transfer_func->tf = TRANSFER_FUNCTION_SRGB;
> > > -   if (stream->signal == SIGNAL_TYPE_HDMI_TYPE_A)
> > > -           adjust_colour_depth_from_display_info(timing_out, info);
> > > +   if (stream->signal == SIGNAL_TYPE_HDMI_TYPE_A) {
> > > +           if (!adjust_colour_depth_from_display_info(timing_out, info) &&
> > > +               drm_mode_is_420_also(info, mode_in) &&
> > > +               timing_out->pixel_encoding != PIXEL_ENCODING_YCBCR420) {
> > > +                   timing_out->pixel_encoding = PIXEL_ENCODING_YCBCR420;
> > > +                   adjust_colour_depth_from_display_info(timing_out, info);
> > > +           }
> > > +   }
> > >  }
> > >
> > >  static void fill_audio_info(struct audio_info *audio_info,
> > > --
> > > 2.24.0.393.g34dc348eaf-goog
> > >
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