drm/i915: Add a FIXME about FBC vs. fence. 90/270 degree rotation

Currently the FBC code doesn't handle the 90/270 degree rotated case
correctly. We would need the GTT tracking to monitor the fence on the
normal GTT view (the rotated view doesn't even have a fence). Not quite
sure how we should program the fence Y offset etc. in that case. For now
we'll end up disabling FBC with 90/270 degree rotation. Add a FIXME
to remind people about this fact.

v2: Reword the text (Chris)
    Move the FIXME to the fbc code

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180221160235.11134-7-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>

diff --git a/drivers/gpu/drm/i915/intel_fbc.c b/drivers/gpu/drm/i915/intel_fbc.c
index 17f6d5deeb383a8c6f4eb7c8656ed294061c082c..bd818131087989ea155fa7a29d6aaec9d3428c38 100644 (file)
--- a/drivers/gpu/drm/i915/intel_fbc.c
+++ b/drivers/gpu/drm/i915/intel_fbc.c
@@ -810,6 +810,12 @@ static bool intel_fbc_can_activate(struct intel_crtc *crtc)
         * Note that is possible for a tiled surface to be unmappable (and
         * so have no fence associated with it) due to aperture constaints
         * at the time of pinning.
+        *
+        * FIXME with 90/270 degree rotation we should use the fence on
+        * the normal GTT view (the rotated view doesn't even have a
+        * fence). Would need changes to the FBC fence Y offset as well.
+        * For now this will effecively disable FBC with 90/270 degree
+        * rotation.
         */
        if (!(cache->flags & PLANE_HAS_FENCE)) {
                fbc->no_fbc_reason = "framebuffer not tiled or fenced";