[now bisected] i915: 2.6.36-rc2 hoses my Intel display

[Chris Wilson]

On Mon, 23 Aug 2010 15:17:08 -0600, Jonathan Corbet <corbet at lwn.net> wrote:
> I went ahead and bisected the problem, which was added between -rc1 and
> -rc2.  The end result is this:

Taking the patch at face value, the cause should be a mistake in error
handling. So the first step would be to identify which i2c_transfer()
failed.

diff --git a/drivers/gpu/drm/i915/intel_sdvo.c b/drivers/gpu/drm/i915/intel_sdvo.c
index 093e914..6afc7cf 100644
--- a/drivers/gpu/drm/i915/intel_sdvo.c
+++ b/drivers/gpu/drm/i915/intel_sdvo.c
@@ -269,7 +269,7 @@ static bool intel_sdvo_read_byte(struct intel_sdvo *intel_sdvo, u8 addr, u8 *ch)
 		return true;
 	}
 
-	DRM_DEBUG_KMS("i2c transfer returned %d\n", ret);
+	WARN(1, "i2c transfer failed, ret=%d\n", ret);
 	return false;
 }
 
@@ -284,8 +284,13 @@ static bool intel_sdvo_write_byte(struct intel_sdvo *intel_sdvo, int addr, u8 ch
 			.buf = out_buf,
 		}
 	};
+	int ret;
+
+	if ((ret = i2c_transfer(intel_sdvo->base.i2c_bus, msgs, 1)) == 1)
+		return true;
 
-	return i2c_transfer(intel_sdvo->base.i2c_bus, msgs, 1) == 1;
+	WARN(1, "i2c transfer failed, ret=%d\n", ret);
+	return false;
 }
 
 #define SDVO_CMD_NAME_ENTRY(cmd) {cmd, #cmd}

-- 
Chris Wilson, Intel Open Source Technology Centre