meson: Enabling full-range HDMI output

Fri Oct 25 01:57:16 PDT 2024

On Thu, Oct 24, 2024 at 8:51 AM Neil Armstrong
<neil.armstrong at linaro.org> wrote:
>
> On 24/10/2024 10:38, neil.armstrong at linaro.org wrote:
> > On 23/10/2024 14:12, Francisco Ayala Le Brun wrote:
> >> Thank you for your response. I can confirm reverting the commit solves
> >> the issue. However, it only leaves me more confused as to the root
> >> cause.
> >>
> >> If dw-hdmi is set to output RGB, and you set the CSC matrix to zeroes,
> >> then it will show a correctly completely black output. However, if you
> >> set the first column of the YUV-to-RGB matrix to ones, and show a
> >> black image via DRM, then the tone is in the limited range. This
> >> seemed to indicate dw-hdmi can output full range RGB, and the problem
> >> was farther upstream.
> >>
> >> Perhaps the problem is the CSC matrices? I was under the assumption
> >> 0x2000 corresponded to 1, even though i.MX6 manual chapter 33 seems to
> >> suggest with a csc_scale of 1, then 0x800 would correspond to 1.
> >> Still, I would expect at least fully black to be correct as that would
> >> give a multiplication by zero.
> >>
> >> Or the state of dw_hdmi is affecting the VIU in some way? Perhaps the
> >> VIU hardware is made to clamp luminance when dw_hdmi is outputting
> >> RGB? I noticed for the CSC there is only a special matrix for
> >> RGB-to-limited-RGB, but no special matrix for YUV-to-limited-RGB. That
> >> seems to suggest the clamping may be done upstream in those cases.
> >>
> >> Francisco
> >>
> >>
> >> On Wed, Oct 23, 2024 at 8:30 AM <neil.armstrong at linaro.org> wrote:
> >>>
> >>> Hi,
> >>>
> >>> On 23/10/2024 10:00, Francisco Ayala Le Brun wrote:
> >>>> Hello,
> >>>>
> >>>> I am seeking some guidance regarding enabling full-range HDMI output.
> >>>> Specifically, I am wondering which component in the video pipeline
> >>>> could be clamping HDMI output values to 16-235? Further details
> >>>> follow:
> >>>>
> >>>> I have been trying to get full-range HDMI output from a Le Potato
> >>>> s905x SBC. At the moment, HDMI output seems to be hard-coded to color
> >>>> quantization limited range (16-235). This greatly diminishes the
> >>>> contrast in full range displays.
> >>>>
> >>>> So far setting the VIU_OSD1/2_FULL_RANGE bit in the
> >>>> VIU_OSD1/2_CTRL_STAT2 register does not seem to work. I have also
> >>>> looked at the color space conversion matrix in dw_hdmi in case that is
> >>>> the culprit, but the values seem fine and setting that to zero does
> >>>> produce a signal in the full range (0). The buffer from the VIU is
> >>>> using a YUV format so dw_hdmi is not using the full to limited range
> >>>> conversion matrix.
> >>>
> >>> Indeed the internal VPU pipeline is in 10bit YUV444, so it requires enabling
> >>> the dw-hdmi CSC, so perhaps those are not designed to output full-range RGB ?
> >>>
> >>> Could you revert:
> >>> d3d6b1bf85ae drm: bridge: dw_hdmi: fix preference of RGB modes over YUV420
> >>>
> >>> This would give you direct YUV444 HDMI output without CSC involved, reverting
> >>> is not an options because of low-cost HDMI panels lying in their EDID
> >>> and not really supporting YUV HDMI...
> >>>
> >>> So if the original YUV is in full range, the culprit is in the DW-HDMI CSC
> >>> table.
> >
> > So seems the current CSC tables outputs limited range from YUV, could you try:
> >
> > =================><==================================
> > diff --git a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > index 0031f3c54882..9e1cb9be4622 100644
> > --- a/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > +++ b/drivers/gpu/drm/bridge/synopsys/dw-hdmi.c
> > @@ -1769,8 +1769,11 @@ static void hdmi_config_AVI(struct dw_hdmi *hdmi,
> >          drm_hdmi_avi_infoframe_from_display_mode(&frame, connector, mode);
> >
> >          if (hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_out_bus_format)) {
> > +               bool is_input_rgb = hdmi_bus_fmt_is_rgb(hdmi->hdmi_data.enc_in_bus_format);
> > +               bool is_limited_range = hdmi->hdmi_data.rgb_limited_range |!is_input_rgb;
>
> Of course:
>
>               bool is_limited_range = hdmi->hdmi_data.rgb_limited_range || !is_input_rgb;
>
> Sorry for the typo.
>
> > +
> >                  drm_hdmi_avi_infoframe_quant_range(&frame, connector, mode,
> > -                                                  hdmi->hdmi_data.rgb_limited_range ?
> > +                                                  is_limited_range ?
> >                                                     HDMI_QUANTIZATION_RANGE_LIMITED :
> >                                                     HDMI_QUANTIZATION_RANGE_FULL);
> >          } else {
> > =================><==================================
> >
> > It won't output full range, but at least the monitor will know the real
> > signal quant range.
> >
> > The real fix would be to calculate some new parameters for full range,
> > but I'm not able to do that personally.
> >
> > Neil
> >
> >>>
> >>> Neil
> >>>
> >>>>
> >>>> Thank you in advance,
> >>>> Francisco
> >>>>
> >>>> _______________________________________________
> >>>> linux-amlogic mailing list
> >>>> linux-amlogic at lists.infradead.org
> >>>> http://lists.infradead.org/mailman/listinfo/linux-amlogic
> >>>
> >>>
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> >
> >
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>

Thank you for the patch. However, it does not fix the issue in the
panel I am using. Perhaps it does not support limited quantization
range at all.

Hopefully I can have a look at the CSC tables soon.

Francisco