drm/i915/skl: Don't try to update plane watermarks if they haven't changed

i915 sometimes needs to disable planes in the middle of an atomic
commit, and then reenable them later in the same commit. Because of
this, we can't make the assumption that the state of the plane actually
changed. Since the state of the plane hasn't actually changed, neither
have it's watermarks. And if the watermarks hasn't changed then we
haven't populated skl_results with anything, which means we'll end up
zeroing out a plane's watermarks in the middle of the atomic commit
without restoring them later.

Simple reproduction recipe:
 - Get a SKL laptop, launch any kind of X session
 - Get two extra monitors
 - Keep hotplugging both displays (so that the display configuration
   jumps from 1 active pipe to 3 active pipes and back)
 - Eventually underrun

Changes since v1:
 - Fix incorrect use of "it's"
Changes since v2:
 - Add reproduction recipe

Signed-off-by: Lyude <cpaul@redhat.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Fixes: 62e0fb880123 ("drm/i915/skl: Update plane watermarks atomically during plane updates")
Signed-off-by: Lyude <cpaul@redhat.com>
Testcase: kms_plane
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1472488288-27280-1-git-send-email-cpaul@redhat.com
Cc: drm-intel-fixes@lists.freedesktop.org

diff --git a/drivers/gpu/drm/i915/intel_display.c b/drivers/gpu/drm/i915/intel_display.c
index 2c05a4c6018f891bd14e61e6dbdaaefa50a639bd..2e7923d80f214db206f58cf13f76fedcbd7b6796 100644 (file)
--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -3448,7 +3448,12 @@ static void skylake_disable_primary_plane(struct drm_plane *primary,
        struct intel_crtc *intel_crtc = to_intel_crtc(crtc);
        int pipe = intel_crtc->pipe;
 
-       skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
+       /*
+        * We only populate skl_results on watermark updates, and if the
+        * plane's visiblity isn't actually changing neither is its watermarks.
+        */
+       if (!crtc->primary->state->visible)
+               skl_write_plane_wm(intel_crtc, &dev_priv->wm.skl_results, 0);
 
        I915_WRITE(PLANE_CTL(pipe, 0), 0);
        I915_WRITE(PLANE_SURF(pipe, 0), 0);

diff --git a/drivers/gpu/drm/i915/intel_sprite.c b/drivers/gpu/drm/i915/intel_sprite.c
index 0df783a66bfb660c08fd32e38e937c1906090d2f..73a521fdf1bdf760e7d487f0e632b80020e43e49 100644 (file)
--- a/drivers/gpu/drm/i915/intel_sprite.c
+++ b/drivers/gpu/drm/i915/intel_sprite.c
@@ -292,8 +292,13 @@ skl_disable_plane(struct drm_plane *dplane, struct drm_crtc *crtc)
        const int pipe = intel_plane->pipe;
        const int plane = intel_plane->plane + 1;
 
-       skl_write_plane_wm(to_intel_crtc(crtc), &dev_priv->wm.skl_results,
-                          plane);
+       /*
+        * We only populate skl_results on watermark updates, and if the
+        * plane's visiblity isn't actually changing neither is its watermarks.
+        */
+       if (!dplane->state->visible)
+               skl_write_plane_wm(to_intel_crtc(crtc),
+                                  &dev_priv->wm.skl_results, plane);
 
        I915_WRITE(PLANE_CTL(pipe, plane), 0);