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.
Signed-off-by: Werner Sembach wse@tuxedocomputers.com --- I did not include the suggested change at intel_hdmi_mode_valid, because as far as I can tell it doesn't make a difference.
From 882afbfd5de6858c01bcef9580305082ce811701 Mon Sep 17 00:00:00 2001
From: Werner Sembach wse@tuxedocomputers.com Date: Mon, 3 May 2021 16:23:17 +0200 Subject: [PATCH 3/3] Use YCbCr420 as fallback when RGB fails
--- drivers/gpu/drm/i915/display/intel_hdmi.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/i915/display/intel_hdmi.c b/drivers/gpu/drm/i915/display/intel_hdmi.c index 2c3b545d5f24..3770ea00930f 100644 --- a/drivers/gpu/drm/i915/display/intel_hdmi.c +++ b/drivers/gpu/drm/i915/display/intel_hdmi.c @@ -1913,7 +1913,7 @@ intel_hdmi_mode_valid(struct drm_connector *connector, clock *= 2; }
- if (drm_mode_is_420_only(&connector->display_info, mode)) + if (connector->ycbcr_420_allowed && drm_mode_is_420(&connector->display_info, mode)) clock /= 2;
status = intel_hdmi_mode_clock_valid(hdmi, clock, has_hdmi_sink); @@ -2125,6 +2125,14 @@ static int intel_hdmi_compute_output_format(struct intel_encoder *encoder, }
ret = intel_hdmi_compute_clock(encoder, crtc_state); + if (ret) { + if (crtc_state->output_format != INTEL_OUTPUT_FORMAT_YCBCR420 && + connector->ycbcr_420_allowed && + drm_mode_is_420_also(&connector->display_info, adjusted_mode)) { + crtc_state->output_format = INTEL_OUTPUT_FORMAT_YCBCR420; + ret = intel_hdmi_compute_clock(encoder, crtc_state); + } + }
return ret; }