drm/radeon/kms: allow rendering while no colorbuffer is set on r300

Because hardware cannot disable all colorbuffers directly to do depth-only
rendering, a user should:
- disable reading from a colorbuffer in blending
- disable fastfill
- set the color channel mask to 0 to prevent writing to a colorbuffer

Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/drivers/gpu/drm/radeon/r100.c b/drivers/gpu/drm/radeon/r100.c
index 84e5df766d3f..71727460968f 100644
--- a/drivers/gpu/drm/radeon/r100.c
+++ b/drivers/gpu/drm/radeon/r100.c
@@ -2881,6 +2881,10 @@ int r100_cs_track_check(struct radeon_device *rdev, struct r100_cs_track *track)
 
         for (i = 0; i < track->num_cb; i++) {
                 if (track->cb[i].robj == NULL) {
+                        if (!(track->fastfill || track->color_channel_mask ||
+                              track->blend_read_enable)) {
+                                continue;
+                        }
                         DRM_ERROR("[drm] No buffer for color buffer %d !\n", i);
                         return -EINVAL;
                 }