[21/29] drm/i915: try another possible DDC bus for the SDVO device with multiple outputs

[Greg KH <gregkh@suse.de>]

2.6.32-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Zhao Yakui <yakui.zhao@intel.com>

commit 7c3f0a2726fed78e0e0afe3b6fc3c1f5b298e447 upstream.

There exist multiple DDC buses for the SDVO cards with multiple outputs.
When we can't get the EDID by using the select DDC bus, we can try the other
possible DDC bus to see whether the EDID can be obtained.

https://bugs.freedesktop.org/show_bug.cgi?id=23842

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Tested-by: Sebastien Caty <sebastien.caty@mrnf.gouv.qc.ca>
Signed-off-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

---
 drivers/gpu/drm/i915/intel_sdvo.c |   26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -1638,6 +1638,32 @@ intel_sdvo_hdmi_sink_detect(struct drm_c
 	edid = drm_get_edid(&intel_output->base,
 			    intel_output->ddc_bus);
 
+	/* This is only applied to SDVO cards with multiple outputs */
+	if (edid == NULL && intel_sdvo_multifunc_encoder(intel_output)) {
+		uint8_t saved_ddc, temp_ddc;
+		saved_ddc = sdvo_priv->ddc_bus;
+		temp_ddc = sdvo_priv->ddc_bus >> 1;
+		/*
+		 * Don't use the 1 as the argument of DDC bus switch to get
+		 * the EDID. It is used for SDVO SPD ROM.
+		 */
+		while(temp_ddc > 1) {
+			sdvo_priv->ddc_bus = temp_ddc;
+			edid = drm_get_edid(&intel_output->base,
+				intel_output->ddc_bus);
+			if (edid) {
+				/*
+				 * When we can get the EDID, maybe it is the
+				 * correct DDC bus. Update it.
+				 */
+				sdvo_priv->ddc_bus = temp_ddc;
+				break;
+			}
+			temp_ddc >>= 1;
+		}
+		if (edid == NULL)
+			sdvo_priv->ddc_bus = saved_ddc;
+	}
 	/* when there is no edid and no monitor is connected with VGA
 	 * port, try to use the CRT ddc to read the EDID for DVI-connector
 	 */