drm/radeon: don't disable plls that are in use by other crtcs

commit 4e58591c upstream.

Some plls are shared for DP.
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>
[bwh: Backported to 3.2: add the dev and rdev variables, previously added
 upstream to support DCE6.1 which isn't supported in this version]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -1578,10 +1578,25 @@ static void atombios_crtc_commit(struct drm_crtc *crtc)
 static void atombios_crtc_disable(struct drm_crtc *crtc)
 {
 	struct radeon_crtc *radeon_crtc = to_radeon_crtc(crtc);
+	struct drm_device *dev = crtc->dev;
+	struct radeon_device *rdev = dev->dev_private;
 	struct radeon_atom_ss ss;
+	int i;
 
 	atombios_crtc_dpms(crtc, DRM_MODE_DPMS_OFF);
 
+	for (i = 0; i < rdev->num_crtc; i++) {
+		if (rdev->mode_info.crtcs[i] &&
+		    rdev->mode_info.crtcs[i]->enabled &&
+		    i != radeon_crtc->crtc_id &&
+		    radeon_crtc->pll_id == rdev->mode_info.crtcs[i]->pll_id) {
+			/* one other crtc is using this pll don't turn
+			 * off the pll
+			 */
+			goto done;
+		}
+	}
+
 	switch (radeon_crtc->pll_id) {
 	case ATOM_PPLL1:
 	case ATOM_PPLL2:
@@ -1592,6 +1607,7 @@ static void atombios_crtc_disable(struct drm_crtc *crtc)
 	default:
 		break;
 	}
+done:
 	radeon_crtc->pll_id = -1;
 }