Re: [PATCH] drm/i915/display Try YCbCr420 color when RGB fails

From: Ville Syrjälä
Date: Fri Apr 30 2021 - 12:56:28 EST

Next message: Alain Volmat: "Re: [PATCH v4 0/7] clk: st: embed clock outputs within drivers"
Previous message: Andrew Lunn: "Re: [PATCH net-next v1 1/1] net: selftest: provide option to disable generic selftests"
In reply to: Werner Sembach: "[PATCH] drm/i915/display Try YCbCr420 color when RGB fails"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]

On Thu, Apr 29, 2021 at 02:05:53PM +0200, Werner Sembach wrote:
> When encoder validation of a display mode fails, retry with less bandwidth
> heavy YCbCr420 color mode, if available. This enables some HDMI 1.4 setups
> to support 4k60Hz output, which previously failed silently.
>
> AMDGPU had nearly the exact same issue. This problem description is
> therefore copied from my commit message of the AMDGPU patch.
>
> On some setups, while the monitor and the gpu support display modes with
> pixel clocks of up to 600MHz, the link encoder might not. This prevents
> YCbCr444 and RGB encoding for 4k60Hz, but YCbCr420 encoding might still be
> possible. However, which color mode is used is decided before the link
> encoder capabilities are checked. This patch fixes the problem by retrying
> to find a display mode with YCbCr420 enforced and using it, if it is
> valid.
>
> I'm not entierly sure if the second
> "if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv))" check in
> intel_hdmi_compute_config(...) after forcing ycbcr420 is necessary. I
> included it to better be safe then sorry.
>
> Signed-off-by: Werner Sembach <wse@xxxxxxxxxxxxxxxxxxx>
> Cc: <stable@xxxxxxxxxxxxxxx>
> ---
> Rebased from 5.12 to drm-tip and resend to resolve merge conflict.
>
> >From 876c1c8d970ff2a411ee8d08651bd4edbe9ecb3d Mon Sep 17 00:00:00 2001
> From: Werner Sembach <wse@xxxxxxxxxxxxxxxxxxx>
> Date: Thu, 29 Apr 2021 13:59:30 +0200
> Subject: [PATCH] Retry using YCbCr420 encoding if clock setup for RGB fails
>
> ---
> drivers/gpu/drm/i915/display/intel_hdmi.c | 80 +++++++++++++++++------
> 1 file changed, 60 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c
> index 46de56af33db..c9b5a7d7f9c6 100644
> --- a/drivers/gpu/drm/i915/display/intel_hdmi.c
> +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c
> @@ -1861,6 +1861,30 @@ static int intel_hdmi_port_clock(int clock, int bpc)
> return clock * bpc / 8;
> }
>
> +static enum drm_mode_status
> +intel_hdmi_check_bpc(struct intel_hdmi *hdmi, int clock, bool has_hdmi_sink, struct drm_i915_private *dev_priv)

Don't pass dev_priv. It can be extracted from the intel_hdmi.

The name of the function isn't really sitting super well with me.
I guess I'd just call it something like intel_hdmi_mode_clock_valid().

We should also split this big patch up into smaller parts. Just this
mechanical extraction of this function without any functional changes
could be a nice first patch in the series.

> +{
> + enum drm_mode_status status;
> +
> + /* check if we can do 8bpc */
> + status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 8),
> + true, has_hdmi_sink);
> +
> + if (has_hdmi_sink) {
> + /* if we can't do 8bpc we may still be able to do 12bpc */
> + if (status != MODE_OK && !HAS_GMCH(dev_priv))
> + status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 12),
> + true, has_hdmi_sink);
> +
> + /* if we can't do 8,12bpc we may still be able to do 10bpc */
> + if (status != MODE_OK && DISPLAY_VER(dev_priv) >= 11)
> + status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 10),
> + true, has_hdmi_sink);
> + }
> +
> + return status;
> +}
> +
> static enum drm_mode_status
> intel_hdmi_mode_valid(struct drm_connector *connector,
> struct drm_display_mode *mode)
> @@ -1891,23 +1915,18 @@ intel_hdmi_mode_valid(struct drm_connector *connector,
> if (drm_mode_is_420_only(&connector->display_info, mode))
> clock /= 2;
>
> - /* check if we can do 8bpc */
> - status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 8),
> - true, has_hdmi_sink);
> + status = intel_hdmi_check_bpc(hdmi, clock, has_hdmi_sink, dev_priv);
>
> - if (has_hdmi_sink) {
> - /* if we can't do 8bpc we may still be able to do 12bpc */
> - if (status != MODE_OK && !HAS_GMCH(dev_priv))
> - status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 12),
> - true, has_hdmi_sink);
> + if (status != MODE_OK) {
> + if (drm_mode_is_420_also(&connector->display_info, mode)) {

We also need a connector->ycbcr_420_allowed check here.

> + /* if we can't do full color resolution we may still be able to do reduced color resolution */
> + clock /= 2;
>
> - /* if we can't do 8,12bpc we may still be able to do 10bpc */
> - if (status != MODE_OK && DISPLAY_VER(dev_priv) >= 11)
> - status = hdmi_port_clock_valid(hdmi, intel_hdmi_port_clock(clock, 10),
> - true, has_hdmi_sink);
> + status = intel_hdmi_check_bpc(hdmi, clock, has_hdmi_sink, dev_priv);
> + }
> + if (status != MODE_OK)
> + return status;
> }
> - if (status != MODE_OK)
> - return status;
>
> return intel_mode_valid_max_plane_size(dev_priv, mode, false);
> }
> @@ -1990,14 +2009,17 @@ static bool hdmi_deep_color_possible(const struct intel_crtc_state *crtc_state,
>
> static int
> intel_hdmi_ycbcr420_config(struct intel_crtc_state *crtc_state,
> - const struct drm_connector_state *conn_state)
> + const struct drm_connector_state *conn_state,
> + const bool force_ycbcr420)
> {
> struct drm_connector *connector = conn_state->connector;
> struct drm_i915_private *i915 = to_i915(connector->dev);
> const struct drm_display_mode *adjusted_mode =
> &crtc_state->hw.adjusted_mode;
>
> - if (!drm_mode_is_420_only(&connector->display_info, adjusted_mode))
> + if (!(drm_mode_is_420_only(&connector->display_info, adjusted_mode) ||
> + (force_ycbcr420 &&
> + drm_mode_is_420_also(&connector->display_info, adjusted_mode))))
> return 0;
>

This function I think we just want to throw out and roll something
a bit better.

Something like this I believe should work nicely:

intel_hdmi_compute_output_format()
{
if (drm_mode_is_420_only())
crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
else
crtc_state->output_format = INTEL_OUTPUT_FORMAT_RGB;

ret = intel_hdmi_compute_clock();
if (ret) {
if (crtc_state->output_format == INTEL_OUTPUT_FORMAT_YCBCR420)
return ret;

crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;

ret = intel_hdmi_compute_clock()
if (ret)
return ret;
}

return 0;
}

assuming we make intel_hdmi_compute_clock() check whether 420 output
is actually supported.

Could roll a small helper for that. Something along these lines perhaps:
static bool intel_hdmi_ycbcr_420_supported()
{
return connector->ycbcr_420_allowed &&
(drm_mode_is_420_only() || drm_mode_is_420_also());
}

The intel_pch_panel_fitting() call should probably just be hoisted
into intel_hdmi_compute_config() after we've called the new
intel_hdmi_compute_output_format().

I think a three patch series is probably what we want for this:
patch 1: extract intel_hdmi_mode_clock_valid() without 420_also handling
patch 2: introduce intel_hdmi_compute_output_format() without 420_also handling
patch 3: drop in the 420_also handling everywhere

That way if there's any regression due to the 420_also stuff at least
we won't have to revert the whole thing, and can then more easily work
on fixing whatever needs fixing.

> if (!connector->ycbcr_420_allowed) {
> @@ -2126,7 +2148,7 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
> struct drm_display_mode *adjusted_mode = &pipe_config->hw.adjusted_mode;
> struct drm_connector *connector = conn_state->connector;
> struct drm_scdc *scdc = &connector->display_info.hdmi.scdc;
> - int ret;
> + int ret, ret_saved;
>
> if (adjusted_mode->flags & DRM_MODE_FLAG_DBLSCAN)
> return -EINVAL;
> @@ -2141,7 +2163,7 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
> if (adjusted_mode->flags & DRM_MODE_FLAG_DBLCLK)
> pipe_config->pixel_multiplier = 2;
>
> - ret = intel_hdmi_ycbcr420_config(pipe_config, conn_state);
> + ret = intel_hdmi_ycbcr420_config(pipe_config, conn_state, false);
> if (ret)
> return ret;
>
> @@ -2155,8 +2177,26 @@ int intel_hdmi_compute_config(struct intel_encoder *encoder,
> intel_hdmi_has_audio(encoder, pipe_config, conn_state);
>
> ret = intel_hdmi_compute_clock(encoder, pipe_config);
> - if (ret)
> - return ret;
> + if (ret) {
> + ret_saved = ret;
> +
> + ret = intel_hdmi_ycbcr420_config(pipe_config, conn_state, true);
> + if (ret)
> + return ret;
> +
> + if (pipe_config->output_format != INTEL_OUTPUT_FORMAT_YCBCR420)
> + return ret_saved;
> +
> + pipe_config->limited_color_range =
> + intel_hdmi_limited_color_range(pipe_config, conn_state);
> +
> + if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv))
> + pipe_config->has_pch_encoder = true;
> +
> + ret = intel_hdmi_compute_clock(encoder, pipe_config);
> + if (ret)
> + return ret;
> + }
>
> if (conn_state->picture_aspect_ratio)
> adjusted_mode->picture_aspect_ratio =
> --
> 2.25.1
>
> _______________________________________________
> dri-devel mailing list
> dri-devel@xxxxxxxxxxxxxxxxxxxxx
> https://lists.freedesktop.org/mailman/listinfo/dri-devel

--
Ville Syrjälä
Intel

Next message: Alain Volmat: "Re: [PATCH v4 0/7] clk: st: embed clock outputs within drivers"
Previous message: Andrew Lunn: "Re: [PATCH net-next v1 1/1] net: selftest: provide option to disable generic selftests"
In reply to: Werner Sembach: "[PATCH] drm/i915/display Try YCbCr420 color when RGB fails"
Messages sorted by: [ date ] [ thread ] [ subject ] [ author ]