[Intel-gfx] [PATCH] drm/i915: check whether we actually received an edid in detect_ddc

[Daniel Vetter]

Somehow detect_ddc manages to fall through all checks when we think
that something responds on the ddc i2c address, but the edid read
failed. Fix this up by explicitly checking for this case.

This fixes a regression on newer chips because since

commit aaa377302b2994fcc2c66741b47da33feb489dca
Author: Daniel Vetter <daniel.vetter at ffwll.ch>
Date:   Sat Jun 16 15:30:32 2012 +0200

    drm/i915/crt: Do not rely upon the HPD presence pin

we use ddc detection also on hotplug capable platforms. And one of
these reads all 0s for any i2c transaction if nothing is connected to
the vga port.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=51900
Tested-by: Yang Guang <guang.a.yang at intel.com>
Signed-Off-by: Daniel Vetter <daniel.vetter at ffwll.ch>
---
 drivers/gpu/drm/i915/intel_crt.c |    3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_crt.c b/drivers/gpu/drm/i915/intel_crt.c
index 61d55d3..540561c 100644
--- a/drivers/gpu/drm/i915/intel_crt.c
+++ b/drivers/gpu/drm/i915/intel_crt.c
@@ -353,6 +353,9 @@ static bool intel_crt_detect_ddc(struct drm_connector *connector)
 			is_digital = edid->input & DRM_EDID_INPUT_DIGITAL;
 			connector->display_info.raw_edid = NULL;
 			kfree(edid);
+		} else {
+			DRM_DEBUG_KMS("CRT not detected via DDC:0x50 [no valid EDID found]\n");
+			return false;
 		}
 
 		if (!is_digital) {
-- 
1.7.10