Thanks for the feedback. I got some questions below.
> 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;
> }
Can you give clarification on the 3 checks coming in between intel_hdmi_ycbcr420_config and intel_hdmi_compute_clock?
I guess this can be done before:
pipe_config->has_audio =
intel_hdmi_has_audio(encoder, pipe_config, conn_state);
This one behaves differently whether or not RGB or YCbCr is used, but I guess does not change the required clock speed? I'm unsure about this however. If it has no effect on the clock I would call it after intel_hdmi_compute_clock:
pipe_config->limited_color_range =
intel_hdmi_limited_color_range(pipe_config, conn_state);
I don't know what this actually does, but it doesn't seem to have to do something with color encoding so, like the has_audio check, it can be done before deciding on RGB or YCbCr420? Correct me if I'm wrong:
if (HAS_PCH_SPLIT(dev_priv) && !HAS_DDI(dev_priv))
pipe_config->has_pch_encoder = true;
> assuming we make intel_hdmi_compute_clock() check whether 420 output
> is actually supported.
Currently it's check ycbcr420 then set. This would turn this around. Check first is more logical for my brain however.
what about something like this?
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 ||
!drm_mode_is_420_also() ||
!connector->ycbcr_420_allowed)
return ret;
crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420;
ret = intel_hdmi_compute_clock()
if (ret)
return ret;
}
return 0;
}
> 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
>>
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