drm/i915: don't force full modeset if primary plane is disabled (v2)

In a future patch, we'll allow the primary plane to be disabled by
userspace via the universal plane API.  If a modeset is requested while
the primary plane is disabled, crtc->primary->fb will be NULL which
generally triggers a full modeset (except in fastboot situations).  If
we detect that the crtc is active, but there's no primary plane fb,
we should still allow a simple plane update rather than a full modeset
if the mode isn't actually changing (after re-enabling the primary plane
of course).

v2:
 - Enable plane after set_base to avoid enabling the plane if set_base
   fails, and to make flip+enable atomic (suggested by Ville)
 - Drop BUG to WARN if we somehow enter the 'fb_changed' modeset case
   with the crtc disabled (suggested by Ville)

Reviewed-by: Chon Ming Lee <chon.ming.lee@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

1 files changed, 21 insertions, 2 deletions

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 8635bb7878fe..d99be95276d1 100644
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -10562,12 +10562,17 @@ intel_set_config_compute_mode_changes(struct drm_mode_set *set,
         if (is_crtc_connector_off(set)) {
                 config->mode_changed = true;
         } else if (set->crtc->primary->fb != set->fb) {
-                /* If we have no fb then treat it as a full mode set */
+                /*
+                 * If we have no fb, we can only flip as long as the crtc is
+                 * active, otherwise we need a full mode set.  The crtc may
+                 * be active if we've only disabled the primary plane, or
+                 * in fastboot situations.
+                 */
                 if (set->crtc->primary->fb == NULL) {
                         struct intel_crtc *intel_crtc =
                                 to_intel_crtc(set->crtc);
 
-                        if (intel_crtc->active && i915.fastboot) {
+                        if (intel_crtc->active) {
                                 DRM_DEBUG_KMS("crtc has no fb, will flip\n");
                                 config->fb_changed = true;
                         } else {
@@ -10805,10 +10810,24 @@ static int intel_crtc_set_config(struct drm_mode_set *set)
                 ret = intel_set_mode(set->crtc, set->mode,
                                      set->x, set->y, set->fb);
         } else if (config->fb_changed) {
+                struct drm_i915_private *dev_priv = dev->dev_private;
+                struct intel_crtc *intel_crtc = to_intel_crtc(set->crtc);
+
                 intel_crtc_wait_for_pending_flips(set->crtc);
 
                 ret = intel_pipe_set_base(set->crtc,
                                           set->x, set->y, set->fb);
+
+                /*
+                 * We need to make sure the primary plane is re-enabled if it
+                 * has previously been turned off.
+                 */
+                if (!intel_crtc->primary_enabled && ret == 0) {
+                        WARN_ON(!intel_crtc->active);
+                        intel_enable_primary_hw_plane(dev_priv, intel_crtc->plane,
+                                                      intel_crtc->pipe);
+                }
+
                 /*
                  * In the fastboot case this may be our only check of the
                  * state after boot.  It would be better to only do it on