Re: [PATCH 4/9] drm/i915/dp: Restructure the sink/output format selection

Nautiyal, Ankit K
2026-04-06T05:32:15Z

On 3/31/2026 7:05 PM, Nicolas Frattaroli wrote:
> On Tuesday, 31 March 2026 01:53:34 Central European Summer Time Ville Syrjala wrote:
>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>
>> Restructure intel_dp_compute_output_format() to resemble the new
>> intel_hdmi_compute_output_formats().
>>
>> Again, we basically have two main code paths:
>> - YCbCr 4:2:0 only modes
>> - everything else including YCbCr 4:2:0 also modes
>>
>> Take the exact same approach with the DP code, making the
>> format selection much less convoluted.
>>
>> Cc: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>> ---
>> drivers/gpu/drm/i915/display/intel_dp.c | 98 +++++++++++++++++--------
>> 1 file changed, 69 insertions(+), 29 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
>> index 4955bd8b11d7..230b45acde29 100644
>> --- a/drivers/gpu/drm/i915/display/intel_dp.c
>> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
>> @@ -1371,6 +1371,28 @@ intel_dp_mode_valid_downstream(struct intel_connector *connector,
>> return MODE_OK;
>> }
>>
>> +static enum drm_mode_status
>> +intel_dp_sink_format_valid(struct intel_connector *connector,
>> + const struct drm_display_mode *mode,
>> + enum intel_output_format sink_format)
>> +{
>> + const struct drm_display_info *info = &connector->base.display_info;
>> +
>> + switch (sink_format) {
>> + case INTEL_OUTPUT_FORMAT_YCBCR420:
>> + if (!connector->base.ycbcr_420_allowed ||
>> + !drm_mode_is_420(info, mode))
>> + return MODE_NO_420;
>> +
>> + return MODE_OK;
>> + case INTEL_OUTPUT_FORMAT_RGB:
>> + return MODE_OK;
>> + default:
>> + MISSING_CASE(sink_format);
>> + return MODE_BAD;
>> + }
>> +}
>> +
> I think here we'll want another
> ---
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index e23162fc3f8b..a1dc089c54f5 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -1373,6 +1373,11 @@ intel_dp_sink_format_valid(struct intel_connector *connector,
>
> return MODE_OK;
> case INTEL_OUTPUT_FORMAT_RGB:
> + return MODE_OK;
> + case INTEL_OUTPUT_FORMAT_YCBCR444:
> + if (!(info->color_formats & BIT(DRM_OUTPUT_COLOR_FORMAT_YCBCR444)))
> + return MODE_BAD;
> +
> return MODE_OK;
> default:
> MISSING_CASE(sink_format);
> ---
>
> though this time, no bpc related changes. With that fixed, I get
> YCbCr444 at 10bpc as well as 8bpc. Can't test 4:2:0 for what appears
> to be unrelated userspace reasons, though the KMS property's enum
> value is exposed properly.

Hmm... this alone should not be sufficient till we actually have code to
try with YCBCR444 in intel_dp_compute_formats().

>
>> int intel_dp_max_hdisplay_per_pipe(struct intel_display *display)
>> {
>> return DISPLAY_VER(display) >= 30 ? 6144 : 5120;
>> @@ -3330,41 +3352,59 @@ static int
>> intel_dp_compute_output_format(struct intel_encoder *encoder,
>> struct intel_crtc_state *crtc_state,
>> struct drm_connector_state *conn_state,
>> - bool respect_downstream_limits)
>> + bool respect_downstream_limits,
>> + enum intel_output_format sink_format)
>> {
>> - struct intel_display *display = to_intel_display(encoder);
>> struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>> struct intel_connector *connector = intel_dp->attached_connector;
>> - const struct drm_display_info *info = &connector->base.display_info;
>> const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
>> - bool ycbcr_420_only;
>> - int ret;
>>
>> - ycbcr_420_only = drm_mode_is_420_only(info, adjusted_mode);
>> -
>> - if (ycbcr_420_only && !connector->base.ycbcr_420_allowed) {
>> - drm_dbg_kms(display->drm,
>> - "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");
>> - crtc_state->sink_format = INTEL_OUTPUT_FORMAT_RGB;
>> - } else {
>> - crtc_state->sink_format = intel_dp_sink_format(connector, adjusted_mode);
>> - }
>> + if (intel_dp_sink_format_valid(connector, adjusted_mode,
>> + sink_format) != MODE_OK)
>> + return -EINVAL;
>>
>> + crtc_state->sink_format = sink_format;
>> crtc_state->output_format = intel_dp_output_format(connector, crtc_state->sink_format);
>>
>> - ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
>> - respect_downstream_limits);
>> - if (ret) {
>> - if (crtc_state->sink_format == INTEL_OUTPUT_FORMAT_YCBCR420 ||
>> - !connector->base.ycbcr_420_allowed ||
>> - !drm_mode_is_420_also(info, adjusted_mode))
>> - return ret;
>> -
>> - crtc_state->sink_format = INTEL_OUTPUT_FORMAT_YCBCR420;
>> - crtc_state->output_format = intel_dp_output_format(connector,
>> - crtc_state->sink_format);
>> - ret = intel_dp_compute_link_config(encoder, crtc_state, conn_state,
>> - respect_downstream_limits);
>> + return intel_dp_compute_link_config(encoder, crtc_state, conn_state,
>> + respect_downstream_limits);
> With the removal of intel_dp_sink_format in this function, I wonder
> if we can get rid of it entirely now. It's only called in
> intel_dp_mode_min_link_bpp_x16, which seems to be used for bandwidth
> limitation calculations (where YCbCr444 vs RGB444 doesn't matter, so
> we're fine in that regard).

I agree we can remove intel_dp_sink_format() but IMO it should be after
patch#7 where we are validating sink format for mode valid.

I guess, with that change, intel_dp_mode_min_link_bpp_x16() can be
passed the sink_format directly since we have already validated that.

Regards,

Ankit

>
> Judging by the "min" in the function name, I assume it should be
> using INTEL_OUTPUT_FORMAT_YCBCR420 in drm_mode_is_420_also cases,
> whereas right now it only gets this from intel_dp_sink_format if
> the mode is drm_mode_is_420_only. So I think removing
> intel_dp_sink_format entirely as a follow-up, and folding a
> corrected minimum bandwidth computation that uses 420 if
> drm_mode_is_420 into intel_dp_mode_min_link_bpp_x16 would make
> sense, unless I'm totally misunderstanding the code here.
>
>> +}
>> +
>> +static int
>> +intel_dp_compute_formats(struct intel_encoder *encoder,
>> + struct intel_crtc_state *crtc_state,
>> + struct drm_connector_state *conn_state,
>> + bool respect_downstream_limits)
>> +{
>> + struct intel_display *display = to_intel_display(encoder);
>> + struct intel_dp *intel_dp = enc_to_intel_dp(encoder);
>> + struct intel_connector *connector = intel_dp->attached_connector;
>> + const struct drm_display_info *info = &connector->base.display_info;
>> + const struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
>> + int ret;
>> +
>> + if (drm_mode_is_420_only(info, adjusted_mode)) {
>> + ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
>> + respect_downstream_limits,
>> + INTEL_OUTPUT_FORMAT_YCBCR420);
>> +
>> + if (ret) {
>> + drm_dbg_kms(display->drm,
>> + "YCbCr 4:2:0 mode but YCbCr 4:2:0 output not possible. Falling back to RGB.\n");
>> +
>> + ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
>> + respect_downstream_limits,
>> + INTEL_OUTPUT_FORMAT_RGB);
>> + }
>> + } else {
>> + ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
>> + respect_downstream_limits,
>> + INTEL_OUTPUT_FORMAT_RGB);
>> +
>> + if (ret && drm_mode_is_420_also(info, adjusted_mode))
>> + ret = intel_dp_compute_output_format(encoder, crtc_state, conn_state,
>> + respect_downstream_limits,
>> + INTEL_OUTPUT_FORMAT_YCBCR420);
>> }
>>
>> return ret;
>> @@ -3539,9 +3579,9 @@ intel_dp_compute_config(struct intel_encoder *encoder,
>> * Try to respect downstream TMDS clock limits first, if
>> * that fails assume the user might know something we don't.
>> */
>> - ret = intel_dp_compute_output_format(encoder, pipe_config, conn_state, true);
>> + ret = intel_dp_compute_formats(encoder, pipe_config, conn_state, true);
>> if (ret)
>> - ret = intel_dp_compute_output_format(encoder, pipe_config, conn_state, false);
>> + ret = intel_dp_compute_formats(encoder, pipe_config, conn_state, false);
>> if (ret)
>> return ret;
>>
>>
>
>
>