drm/atomic: Filter out redundant DPMS calls

commit de93ddf88088f7624b589d0ff3af9effb87e8f3b upstream.

Video players (eg. mpv) do periodic XResetScreenSaver() calls to
keep the screen on while the video playing. The modesetting ddx
plumbs these straight through into the kernel as DPMS setproperty
ioctls, without any filtering whatsoever. When implemented via
atomic these end up as empty commits on the crtc (which will
nonetheless take one full frame), which leads to a dropped
frame every time XResetScreenSaver() is called.

Let's just filter out redundant DPMS property changes in the
kernel to avoid this issue.

v2: Explain the resulting commits a bit better (Sima)
    Document the behaviour in uapi docs (Sima)

Cc: stable@vger.kernel.org
Testcase: igt/kms_flip/flip-vs-dpms-on-nop
Reviewed-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250219160239.17502-1-ville.syrjala@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/gpu/drm/drm_atomic_uapi.c b/drivers/gpu/drm/drm_atomic_uapi.c
index fb646b12af042e000f3954d7a34b03ca96cc8806..476357fb5c74ad42455d948407f3c9c75c9f9715 100644 (file)
--- a/drivers/gpu/drm/drm_atomic_uapi.c
+++ b/drivers/gpu/drm/drm_atomic_uapi.c
@@ -964,6 +964,10 @@ int drm_atomic_connector_commit_dpms(struct drm_atomic_state *state,
 
        if (mode != DRM_MODE_DPMS_ON)
                mode = DRM_MODE_DPMS_OFF;
+
+       if (connector->dpms == mode)
+               goto out;
+
        connector->dpms = mode;
 
        crtc = connector->state->crtc;

diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
index 1140292820bb164b410e0bf6be20fcb42e645834..fff2038e98035a02c7caedfcfb19567f75503f94 100644 (file)
--- a/drivers/gpu/drm/drm_connector.c
+++ b/drivers/gpu/drm/drm_connector.c
@@ -980,6 +980,10 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
  *     callback. For atomic drivers the remapping to the "ACTIVE" property is
  *     implemented in the DRM core.
  *
+ *     On atomic drivers any DPMS setproperty ioctl where the value does not
+ *     change is completely skipped, otherwise a full atomic commit will occur.
+ *     On legacy drivers the exact behavior is driver specific.
+ *
  *     Note that this property cannot be set through the MODE_ATOMIC ioctl,
  *     userspace must use "ACTIVE" on the CRTC instead.
  *