Radeon regression fix

[Brad Campbell]

This patch fixes a regression introduced between 2.6.39 & 3.1-rc1 
whereby the displayport AUX channel stopped re-trying commands that 
elicited a DEFER response.

Signed-off-by: Brad Campbell <brad at fnarfbargle.com>

diff --git a/drivers/gpu/drm/radeon/atombios_dp.c 
b/drivers/gpu/drm/radeon/atombios_dp.c
index 7ad43c6..b8450f4 100644
--- a/drivers/gpu/drm/radeon/atombios_dp.c
+++ b/drivers/gpu/drm/radeon/atombios_dp.c
@@ -60,11 +60,13 @@ static int radeon_process_aux_ch(struct 
radeon_i2c_chan *chan,
  	int index = GetIndexIntoMasterTable(COMMAND, 
ProcessAuxChannelTransaction);
  	unsigned char *base;
  	int recv_bytes;
+	int retry_count = 0;

  	memset(&args, 0, sizeof(args));

  	base = (unsigned char *)rdev->mode_info.atom_context->scratch;

+retry:
  	memcpy(base, send, send_bytes);

  	args.v1.lpAuxRequest = 0;
@@ -79,6 +81,16 @@ static int radeon_process_aux_ch(struct 
radeon_i2c_chan *chan,

  	*ack = args.v1.ucReplyStatus;

+	/* defer */
+	if (args.v1.ucReplyStatus == 0x20){
+		DRM_DEBUG_KMS("dp_aux_ch defer\n");
+			/* 10 is an arbitrary value from the pre-regression patch
+			in practice I've never seen more than one */
+			if (retry_count++ < 10)
+				goto retry;
+		return -EBUSY;
+	}
+
  	/* timeout */
  	if (args.v1.ucReplyStatus == 1) {
  		DRM_DEBUG_KMS("dp_aux_ch timeout\n");