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

[Alex Deucher]

On Thu, Jan 2, 2020 at 10:14 AM Harry Wentland <hwentlan at amd.com> wrote:
>
> On 2019-12-02 4:47 p.m., 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>
>
> Apologies for the late response.
>
> Thanks for getting high-res modes working on HDMI.
>
> This change is
> Reviewed-by: Harry Wentland <harry.wentland at amd.com>
>

Applied.  thanks!

Alex

> Harry
>
> > ---
> >  .../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,
> >
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