A driver whose "scanout" is an expensive encode-and-send (like a USB
display) wants to repaint only the region a client marked dirty rather
than the whole framebuffer every flip. Add two RawPlaneState accessors
over the client's FB_DAMAGE_CLIPS (relative to the old plane state), both
intersected with the visible source area:
- damage_merged(), wrapping drm_atomic_helper_damage_merged(): merges the
clips into one rectangle and returns it as a new Rect type (with
width()/height() helpers). None means nothing to repaint; if the client
supplied no clips, the full plane rectangle is returned, so a driver can
always treat Some as "repaint this box".
- for_each_damage_clip(), driving drm_atomic_helper_damage_iter: invokes a
closure once per individual clip (the rectangles damage_merged() collapses
into one), so a driver that forwards each changed region separately -- e.g.
over USB -- can repaint just those rectangles instead of their bounding box.
drm_atomic_helper_damage_{merged,iter_*} live in <drm/drm_damage_helper.h>,
so add that to bindings_helper.h.
Signed-off-by: Mike Lothian <[email protected]>
Assisted-by: Claude:claude-opus-4-8 [Claude-Code]
---
rust/bindings/bindings_helper.h | 1 +
rust/kernel/drm/kms/plane.rs | 105 ++++++++++++++++++++++++++++++++
2 files changed, 106 insertions(+)
diff --git a/rust/bindings/bindings_helper.h b/rust/bindings/bindings_helper.h
index 7d04abec1215..b8675642c1a8 100644
--- a/rust/bindings/bindings_helper.h
+++ b/rust/bindings/bindings_helper.h
@@ -39,6 +39,7 @@
#include <drm/drm_atomic_helper.h>
#include <drm/drm_connector.h>
#include <drm/drm_crtc.h>
+#include <drm/drm_damage_helper.h>
#include <drm/drm_blend.h>
#include <drm/drm_edid.h>
#include <drm/drm_encoder.h>
diff --git a/rust/kernel/drm/kms/plane.rs b/rust/kernel/drm/kms/plane.rs
index ead875316829..4ae11cec88a4 100644
--- a/rust/kernel/drm/kms/plane.rs
+++ b/rust/kernel/drm/kms/plane.rs
@@ -605,6 +605,49 @@ pub trait FromRawPlaneState: AsRawPlaneState {
unsafe fn from_raw_mut<'a>(ptr: *mut bindings::drm_plane_state) -> &'a mut
Self;
}
+/// A rectangle in a plane's source (pixel) space, as produced by
+/// [`RawPlaneState::damage_merged`].
+///
+/// The box is inclusive on the top-left and exclusive on the bottom-right
(`[x1, x2)` by
+/// `[y1, y2)`), matching [`struct drm_rect`].
+///
+/// [`struct drm_rect`]: srctree/include/drm/drm_rect.h
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
+pub struct Rect {
+ /// Left edge, inclusive.
+ pub x1: i32,
+ /// Top edge, inclusive.
+ pub y1: i32,
+ /// Right edge, exclusive.
+ pub x2: i32,
+ /// Bottom edge, exclusive.
+ pub y2: i32,
+}
+
+impl Rect {
+ #[inline]
+ fn from_raw(r: &bindings::drm_rect) -> Self {
+ Self {
+ x1: r.x1,
+ y1: r.y1,
+ x2: r.x2,
+ y2: r.y2,
+ }
+ }
+
+ /// The width of the rectangle in pixels.
+ #[inline]
+ pub fn width(&self) -> i32 {
+ self.x2 - self.x1
+ }
+
+ /// The height of the rectangle in pixels.
+ #[inline]
+ pub fn height(&self) -> i32 {
+ self.y2 - self.y1
+ }
+}
+
/// Common methods available on any type which implements [`AsRawPlane`].
///
/// This is implemented internally by DRM, and provides many of the basic
methods for working with
@@ -691,6 +734,68 @@ fn atomic_helper_check<S, D>(
})
}
+ /// Merge all frame-damage clips on this (new) plane state -- relative to
`old` -- into a
+ /// single bounding rectangle, intersected with the plane's visible source
area.
+ ///
+ /// Returns [`None`] when the plane is not visible or there is nothing to
update. If the client
+ /// supplied no explicit damage clips, the full plane rectangle is
returned, so a driver can
+ /// always treat [`Some`] as "repaint this rectangle" and fall back to a
full-frame update.
+ /// Coordinates are integer pixels in the plane's source space.
+ ///
+ /// [`drm_atomic_helper_damage_merged`]:
srctree/include/drm/drm_damage_helper.h
+ fn damage_merged(&self, old: &impl AsRawPlaneState) -> Option<Rect> {
+ let mut rect = bindings::drm_rect {
+ x1: 0,
+ y1: 0,
+ x2: 0,
+ y2: 0,
+ };
+
+ // SAFETY:
+ // - `old` and `self` are valid initialized `drm_plane_state`s via
their type invariants.
+ // - `drm_atomic_helper_damage_merged` only reads the two states (to
gather the damage
+ // clips and the source rectangle) and writes the merged result into
`rect`; it does not
+ // mutate the plane state, so deriving a `*mut` from our shared
reference is sound.
+ let visible = unsafe {
+ bindings::drm_atomic_helper_damage_merged(
+ core::ptr::from_ref(old.as_raw()),
+ core::ptr::from_ref(self.as_raw()).cast_mut(),
+ &mut rect,
+ )
+ };
+
+ visible.then(|| Rect::from_raw(&rect))
+ }
+
+ /// Invoke `f` once per frame-damage clip on this (new) plane state
relative to `old`, each
+ /// intersected with the plane's visible source area -- i.e. the
individual rectangles that
+ /// [`Self::damage_merged`] collapses into one. If the client supplied no
explicit damage clips,
+ /// `f` is called once with the full plane rectangle. Coordinates are
integer pixels in the
+ /// plane's source space.
+ ///
+ /// This lets a driver forward each changed region separately (e.g. to a
remote display) instead
+ /// of the bounding box of them all.
+ ///
+ /// [`drm_atomic_helper_damage_iter`]:
srctree/include/drm/drm_damage_helper.h
+ fn for_each_damage_clip(&self, old: &impl AsRawPlaneState, mut f: impl
FnMut(Rect)) {
+ let mut iter = bindings::drm_atomic_helper_damage_iter::default();
+ let mut clip = bindings::drm_rect::default();
+ // SAFETY:
+ // - `old` and `self` are valid initialized `drm_plane_state`s via
their type invariants.
+ // - `drm_atomic_helper_damage_iter_init` only reads the two states to
set up `iter`, and
+ // `_next` only reads `iter` and writes `clip`; neither escapes a
pointer.
+ unsafe {
+ bindings::drm_atomic_helper_damage_iter_init(
+ &mut iter,
+ core::ptr::from_ref(old.as_raw()),
+ core::ptr::from_ref(self.as_raw()),
+ );
+ while bindings::drm_atomic_helper_damage_iter_next(&mut iter, &mut
clip) {
+ f(Rect::from_raw(&clip));
+ }
+ }
+ }
+
/// Return the framebuffer currently set for this plane state
#[inline]
fn framebuffer<D>(&self) -> Option<&Framebuffer<D>>
--
2.55.0
