drm/nouveau/kms/nv50: avoid touching DP_MSTM_CTRL if !DP_MST_CAP

Fixes certain displays not being detected due to DPAUX errors.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

diff --git a/drivers/gpu/drm/nouveau/nv50_display.c b/drivers/gpu/drm/nouveau/nv50_display.c
index a9855a4..8891805 100644 (file)
--- a/drivers/gpu/drm/nouveau/nv50_display.c
+++ b/drivers/gpu/drm/nouveau/nv50_display.c
@@ -3343,12 +3343,15 @@ nv50_mstm_detect(struct nv50_mstm *mstm, u8 dpcd[8], int allow)
        if (!mstm)
                return 0;
 
-       if (dpcd[0] >= 0x12 && allow) {
+       if (dpcd[0] >= 0x12) {
                ret = drm_dp_dpcd_readb(mstm->mgr.aux, DP_MSTM_CAP, &dpcd[1]);
                if (ret < 0)
                        return ret;
 
-               state = dpcd[1] & DP_MST_CAP;
+               if (!(dpcd[1] & DP_MST_CAP))
+                       dpcd[0] = 0x11;
+               else
+                       state = allow;
        }
 
        ret = nv50_mstm_enable(mstm, dpcd[0], state);