linux-kernel - [PATCH 3.12 095/116] drm/i915/dp: fall back to 18 bpp when sink capability is unknown

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Message-Id: <554b014005ab84bb9f1ac8edc4492c6ae5e176f7.1457082108.git.jslaby@suse.cz>
Date:	Fri,  4 Mar 2016 10:02:20 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	stable@...r.kernel.org
Cc:	linux-kernel@...r.kernel.org, Jani Nikula <jani.nikula@...el.com>,
	Jiri Slaby <jslaby@...e.cz>
Subject: [PATCH 3.12 095/116] drm/i915/dp: fall back to 18 bpp when sink capability is unknown

From: Jani Nikula <jani.nikula@...el.com>

3.12-stable review patch.  If anyone has any objections, please let me know.

===============

commit 5efd407674068dede403551bea3b0b134c32513a upstream.

Per DP spec, the source device should fall back to 18 bpp, VESA range
RGB when the sink capability is unknown. Fix the color depth
clamping. 18 bpp color depth should ensure full color range in automatic
mode.

The clamping has been HDMI specific since its introduction in

commit 996a2239f93b03c5972923f04b097f65565c5bed
Author: Daniel Vetter <daniel.vetter@...ll.ch>
Date:   Fri Apr 19 11:24:34 2013 +0200

    drm/i915: Disable high-bpc on pre-1.4 EDID screens

Reported-and-tested-by: Dihan Wickremasuriya <nayomal@...il.com>
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=105331
Reviewed-by: Ville Syrjälä <ville.syrjala@...ux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1452695720-7076-1-git-send-email-jani.nikula@intel.com
(cherry picked from commit 013dd9e038723bbd2aa67be51847384b75be8253)
Signed-off-by: Jiri Slaby <jslaby@...e.cz>
---
 drivers/gpu/drm/i915/intel_display.c | 20 +++++++++++++++-----
 1 file changed, 15 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 37a9d3c89feb..af46a33d8715 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8200,11 +8200,21 @@ connected_sink_compute_bpp(struct intel_connector * connector,
 		pipe_config->pipe_bpp = connector->base.display_info.bpc*3;
 	}
 
-	/* Clamp bpp to 8 on screens without EDID 1.4 */
-	if (connector->base.display_info.bpc == 0 && bpp > 24) {
-		DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of 24\n",
-			      bpp);
-		pipe_config->pipe_bpp = 24;
+	/* Clamp bpp to default limit on screens without EDID 1.4 */
+	if (connector->base.display_info.bpc == 0) {
+		int type = connector->base.connector_type;
+		int clamp_bpp = 24;
+
+		/* Fall back to 18 bpp when DP sink capability is unknown. */
+		if (type == DRM_MODE_CONNECTOR_DisplayPort ||
+		    type == DRM_MODE_CONNECTOR_eDP)
+			clamp_bpp = 18;
+
+		if (bpp > clamp_bpp) {
+			DRM_DEBUG_KMS("clamping display bpp (was %d) to default limit of %d\n",
+				      bpp, clamp_bpp);
+			pipe_config->pipe_bpp = clamp_bpp;
+		}
 	}
 }
 
-- 
2.7.2