Attachment 128761 Details for Bug 99250 – Patch to disable all deep colors when DC_36bit not set

[patch] Patch to disable all deep colors when DC_36bit not set

0001-Disable-deep-color-modes-when-sink-violates-spec.patch (text/plain), 3.70 KB, created by Nicholas Sielicki on 2017-01-04 23:13:52 UTC

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Creator: Nicholas Sielicki

Created: 2017-01-04 23:13:52 UTC

Size: 3.70 KB

patch

obsolete

>From 2c866e31ecf2386fc4ca5f0b83ee8438c99a27d0 Mon Sep 17 00:00:00 2001
>From: Nicholas Sielicki <sielicki@yandex.com>
>Date: Wed, 4 Jan 2017 16:41:39 -0600
>Subject: [PATCH] Disable deep color modes when sink violates spec
>
>As per the HDMI 1.3 and 1.4 spec, "deep color modes" are color depths
>greater than 24 bits per pixel. The spec explicitly states, "All Deep
>Color modes are optional though if an HDMI Source or Sink supports any
>Deep Color mode, it shall support 36-bit mode." (6.2.4 Color Depth
>Requirements).
>
>i915 relies on this being respected. Much of the intel hardware is
>incapable of operating at any bit-per-component setting besides 8 and
>12, and the spec implies that if any deep color support is found that it
>is a safe assumption to operate at 12.
>
>I came across a monitor (Acer X233H) that supplies an illegal EDID where
>DC_30bit is set and DC_36bit is not set. The end result is badly garbled
>output because the driver is sending 36BPP when the monitor can't handle
>it.
>
>This patch ensures that the EDID is within the spec (specifically, that
>DC_36bit is set) _before_ committing going forward with deep colors.
>There was a check for this EDID inconsistency, but it resulted only in a
>warning and did not fall-back to safer settings.
>---
> drivers/gpu/drm/drm_edid.c | 30 ++++++++++++++++++------------
> 1 file changed, 18 insertions(+), 12 deletions(-)
>
>diff --git a/drivers/gpu/drm/drm_edid.c b/drivers/gpu/drm/drm_edid.c
>index 336be31ff3de..6ea5387b30e5 100644
>--- a/drivers/gpu/drm/drm_edid.c
>+++ b/drivers/gpu/drm/drm_edid.c
>@@ -3772,6 +3772,7 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> {
> 	struct drm_display_info *info = &connector->display_info;
> 	unsigned int dc_bpc = 0;
>+	u8 modes = 0;
> 
> 	/* HDMI supports at least 8 bpc */
> 	info->bpc = 8;
>@@ -3781,21 +3782,21 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> 
> 	if (hdmi[6] & DRM_EDID_HDMI_DC_30) {
> 		dc_bpc = 10;
>-		info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_30;
>+		modes |= DRM_EDID_HDMI_DC_30;
> 		DRM_DEBUG("%s: HDMI sink does deep color 30.\n",
> 			  connector->name);
> 	}
> 
> 	if (hdmi[6] & DRM_EDID_HDMI_DC_36) {
> 		dc_bpc = 12;
>-		info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_36;
>+		modes |= DRM_EDID_HDMI_DC_36;
> 		DRM_DEBUG("%s: HDMI sink does deep color 36.\n",
> 			  connector->name);
> 	}
> 
> 	if (hdmi[6] & DRM_EDID_HDMI_DC_48) {
> 		dc_bpc = 16;
>-		info->edid_hdmi_dc_modes |= DRM_EDID_HDMI_DC_48;
>+		modes |= DRM_EDID_HDMI_DC_48;
> 		DRM_DEBUG("%s: HDMI sink does deep color 48.\n",
> 			  connector->name);
> 	}
>@@ -3806,6 +3807,20 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> 		return;
> 	}
> 
>+	/*
>+	 * All deep color modes are optional, but if a sink supports any deep
>+	 * color mode, it must support 36-bit mode. If this is found not
>+	 * to be the case, sink is in violation of HDMI 1.3 / 1.4 spec and it
>+	 * is prudent to diable all deep color modes. Return here before
>+	 * committing bpc and DRM_EDID_DC_XX.
>+	 */
>+	if (modes & ~DRM_EDID_HDMI_DC_36){
>+		DRM_DEBUG("%s: HDMI sink should do DC_36, but does not!\n",
>+			  connector->name);
>+		return;
>+	}
>+
>+	info->edid_hdmi_dc_modes |= modes;
> 	DRM_DEBUG("%s: Assigning HDMI sink color depth as %d bpc.\n",
> 		  connector->name, dc_bpc);
> 	info->bpc = dc_bpc;
>@@ -3823,15 +3838,6 @@ static void drm_parse_hdmi_deep_color_info(struct drm_connector *connector,
> 		DRM_DEBUG("%s: HDMI sink does YCRCB444 in deep color.\n",
> 			  connector->name);
> 	}
>-
>-	/*
>-	 * Spec says that if any deep color mode is supported at all,
>-	 * then deep color 36 bit must be supported.
>-	 */
>-	if (!(hdmi[6] & DRM_EDID_HDMI_DC_36)) {
>-		DRM_DEBUG("%s: HDMI sink should do DC_36, but does not!\n",
>-			  connector->name);
>-	}
> }
> 
> static void
>-- 
>2.11.0
>

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Attachments on bug 99250: 128711 | 128712 | 128761 | 128762 | 128785

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