RE: [EXT] Re: [PATCH v2 3/5] drm: bridge: dw_hdmi: Enable GCP only for Deep Color

[Sandor Yu <sandor.yu@nxp.com>]

> -----Original Message-----
> From: Neil Armstrong <narmstrong@baylibre.com>
> Sent: 2022年4月8日 20:40
> To: Sandor Yu <sandor.yu@nxp.com>; dri-devel@lists.freedesktop.org;
> linux-kernel@vger.kernel.org; andrzej.hajda@intel.com;
> robert.foss@linaro.org; Laurent.pinchart@ideasonboard.com;
> jonas@kwiboo.se; jernej.skrabec@gmail.com; hverkuil-cisco@xs4all.nl
> Cc: S.J. Wang <shengjiu.wang@nxp.com>; cai.huoqing@linux.dev;
> maxime@cerno.tech; harry.wentland@amd.com
> Subject: [EXT] Re: [PATCH v2 3/5] drm: bridge: dw_hdmi: Enable GCP only for
> Deep Color
> 
> Caution: EXT Email
> 
> On 08/04/2022 12:32, Sandor Yu wrote:
> > HDMI1.4b specification section 6.5.3:
> > Source shall only send GCPs with non-zero CD to sinks that indicate
> > support for Deep Color.
> >
> > DW HDMI GCP default enabled, clear gpc_auto bit for 24-bit color depth.
> 
> It's right because we do not handle AVMUTE, Pixel Packing nor
> Default_Phase.
> 
> >
> > Signed-off-by: Sandor Yu <Sandor.yu@nxp.com>
> > ---
> >   drivers/gpu/drm/bridge/synopsys/dw-hdmi.c | 12 ++++++++++++
> >   1 file changed, 12 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > index 02d8f7e08814..5a7ec066e37a 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > @@ -1108,6 +1108,8 @@ static void hdmi_video_packetize(struct
> dw_hdmi *hdmi)
> >       unsigned int output_select =
> HDMI_VP_CONF_OUTPUT_SELECTOR_PP;
> >       struct hdmi_data_info *hdmi_data = &hdmi->hdmi_data;
> >       u8 val, vp_conf;
> > +     u8 clear_gcp_auto = 0;
> > +
> >
> >       if (hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format) ||
> >
> hdmi_bus_fmt_is_yuv444(hdmi->hdmi_data.enc_out_bus_format)
> > || @@ -1117,6 +1119,7 @@ static void hdmi_video_packetize(struct
> dw_hdmi *hdmi)
> >               case 8:
> >                       color_depth = 4;
> >                       output_select =
> > HDMI_VP_CONF_OUTPUT_SELECTOR_BYPASS;
> > +                     clear_gcp_auto = 1;
> >                       break;
> >               case 10:
> >                       color_depth = 5; @@ -1136,6 +1139,7 @@
> static
> > void hdmi_video_packetize(struct dw_hdmi *hdmi)
> >               case 0:
> >               case 8:
> >                       remap_size =
> HDMI_VP_REMAP_YCC422_16bit;
> > +                     clear_gcp_auto = 1;
> >                       break;
> >               case 10:
> >                       remap_size = HDMI_VP_REMAP_YCC422_20bit;
> @@
> > -1160,6 +1164,14 @@ static void hdmi_video_packetize(struct dw_hdmi
> *hdmi)
> >               HDMI_VP_PR_CD_DESIRED_PR_FACTOR_MASK);
> >       hdmi_writeb(hdmi, val, HDMI_VP_PR_CD);
> >
> > +     val = hdmi_readb(hdmi, HDMI_FC_DATAUTO3);
> > +     if (clear_gcp_auto == 1)
> > +             /* disable Auto GCP when 24-bit color */
> 
> Maybe add a new define for HDMI_FC_DATAUTO3_GCP_AUTO bit and use it
> here.
OK, I will add it.
> 
> > +             val &= ~0x4;
> > +     else
> > +             val |= 0x4;
> > +     hdmi_writeb(hdmi, val, HDMI_FC_DATAUTO3);
> 
> Please also add a comment explaining we clear GCP because we only transmit
> CD and do not handle AVMUTE, PP nor Default_Phase (yet).
> 
OK.

Sandor
> > +
> >       hdmi_modb(hdmi,
> HDMI_VP_STUFF_PR_STUFFING_STUFFING_MODE,
> >                 HDMI_VP_STUFF_PR_STUFFING_MASK,
> HDMI_VP_STUFF);
> >
> 
> Thanks,
> Neil