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");