[PATCH 0/2] drm/i915/fbc: Dirty rectangle bounds enforcement and CFB nuke handling

[PATCH 0/2] drm/i915/fbc: Dirty rectangle bounds enforcement and CFB nuke handling

[Austin Hu]

This series improves Frame Buffer Compression (FBC) dirty rectangle
handling in compliance with hardware requirements.

The first patch restricts dirty rectangle vertical coordinates to the
valid frame buffer range [y_offset, y_end], adding explicit coordinate
inversion handling for 180-degree plane rotation and debug logging when
clamping occurs[cite: 10].

The second patch tracks plane state attribute changes during atomic commits[cite: 9].
When FBC Dirty Rectangle mode is active, partial updates only apply to
surface address changes (PLANE_SURF)[cite: 9]. Modifications to any other
plane state parameters require fetching full-plane pixel data from memory to
re-compress and update the entire CFB in stolen memory[cite: 9]. Once fully
re-compressed, subsequent atomic commits can resume selective dirty
rectangle updates[cite: 9].

Austin Hu (1):
  drm/i915/fbc: nuke CFB if Plane setting (except for surf addr) changes[cite: 9]

Charlton Lin (1):
  drm/i915/fbc: fbc_dirty_rect restrictions and logging[cite: 10]

 drivers/gpu/drm/i915/display/intel_fbc.c | 158 +++++++++++++++++++++-[cite: 9, 10]
 1 file changed, 151 insertions(+), 7 deletions(-)[cite: 9, 10]

[PATCH 1/2] drm/i915/fbc: fbc_dirty_rect restrictions and logging

[Austin Hu]

From: Charlton Lin <charlton.lin@intel.com>

Clamp the FBC dirty rectangle coordinates to the valid frame buffer
range [y_offset, y_end] to prevent out-of-bounds coordinates, and
log a debug message when clamping occurs.

Signed-off-by: Charlton Lin <charlton.lin@intel.com>
Signed-off-by: Austin Hu <austin.hu@intel.com>
---
 drivers/gpu/drm/i915/display/intel_fbc.c | 39 ++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
index f61b4a218d6e..c0fed695af0d 100644
--- a/drivers/gpu/drm/i915/display/intel_fbc.c
+++ b/drivers/gpu/drm/i915/display/intel_fbc.c
@@ -1521,11 +1521,14 @@ __intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
 			       const struct intel_crtc_state *crtc_state)
 {
 	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
+	struct intel_display *display = to_intel_display(plane_state);
 	struct intel_fbc *fbc = plane->fbc;
 	struct drm_rect *fbc_dirty_rect = &fbc->state.dirty_rect;
 	int width = drm_rect_width(&plane_state->uapi.src) >> 16;
+	int height = drm_rect_height(&plane_state->uapi.src) >> 16;
 	const struct drm_rect *damage = &plane_state->damage;
 	int y_offset = plane_state->view.color_plane[0].y;
+	int y_end = y_offset + height;
 
 	lockdep_assert_held(&fbc->lock);
 
@@ -1535,11 +1538,41 @@ __intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
 		return;
 	}
 
-	if (drm_rect_visible(damage))
-		*fbc_dirty_rect = *damage;
-	else
+	if (drm_rect_visible(damage)) {
+		int y1, y2;
+
+		if (plane_state->hw.rotation & DRM_MODE_ROTATE_180) {
+			/* Under 180 degree rotation, coordinate system is inverted */
+			int inv_y1 = height - damage->y2;
+			int inv_y2 = height - damage->y1;
+
+			y1 = clamp(y_offset + inv_y1, y_offset, y_end);
+			y2 = clamp(y_offset + inv_y2, y_offset, y_end);
+		} else {
+			y1 = clamp(damage->y1, y_offset, y_end);
+			y2 = clamp(damage->y2, y_offset, y_end);
+		}
+
+		/*
+		 * Clamp dirty rect to the valid FB range [y_offset, y_end].
+		 * Per Bspec:
+		 *   start_line >= y_offset
+		 *   end_line <= y_offset + plane_height
+		 */
+		if (y1 != damage->y1 || y2 != damage->y2)
+			drm_dbg_kms(display->drm,
+				    "[PLANE:%d:%s] FBC dirty rect out of range: y1=%d y2=%d clamped to y1=%d y2=%d (y_offset=%d y_end=%d)\n",
+				    plane->base.base.id, plane->base.name,
+				    damage->y1, damage->y2, y1, y2, y_offset, y_end);
+
+		fbc_dirty_rect->x1 = damage->x1;
+		fbc_dirty_rect->x2 = damage->x2;
+		fbc_dirty_rect->y1 = y1;
+		fbc_dirty_rect->y2 = y2;
+	} else {
 		/* dirty rect must cover at least one line */
 		*fbc_dirty_rect = DRM_RECT_INIT(0, y_offset, width, 1);
+	}
 }
 
 void
-- 
2.34.1

Re: [PATCH 1/2] drm/i915/fbc: fbc_dirty_rect restrictions and logging

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:
- [High] Incorrect coordinate space math in the 180-degree rotation branch causes the FBC dirty rectangle to collapse, breaking FBC tracking.
- [Medium] The 'FBC dirty rect out of range' debug warning will trigger spuriously on almost every frame when the plane is rotated 180 degrees.
--

--- Patch [1]: [PATCH 1/2] drm/i915/fbc: fbc_dirty_rect restrictions and logging ---
commit 234fb7237db4bb8e467458e88cc6ed3f6e850511
Author: Charlton Lin <charlton.lin@intel.com>

drm/i915/fbc: fbc_dirty_rect restrictions and logging

Clamp the FBC dirty rectangle coordinates to the valid frame buffer
range [y_offset, y_end] to prevent out-of-bounds coordinates, and
log a debug message when clamping occurs.

> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index f61b4a218d6ef..c0fed695af0da 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c

[ ... ]

> @@ -1535,11 +1538,41 @@ __intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
>  		return;
>  	}
>  
> -	if (drm_rect_visible(damage))
> -		*fbc_dirty_rect = *damage;
> -	else
> +	if (drm_rect_visible(damage)) {
> +		int y1, y2;
> +
> +		if (plane_state->hw.rotation & DRM_MODE_ROTATE_180) {
> +			/* Under 180 degree rotation, coordinate system is inverted */
> +			int inv_y1 = height - damage->y2;
> +			int inv_y2 = height - damage->y1;
> +
> +			y1 = clamp(y_offset + inv_y1, y_offset, y_end);
> +			y2 = clamp(y_offset + inv_y2, y_offset, y_end);

[Severity: High]
Can this math result in collapsed dirty rectangles?

Because damage->y2 already includes the absolute y_offset, height - damage->y2
yields a large negative number. When y_offset is added back, the result falls
well below y_offset, causing both y1 and y2 to unconditionally clamp to
y_offset.

This collapses the FBC dirty rectangle to a 0-height region starting at
y_offset, entirely missing the actual damaged pixels.

> +		} else {
> +			y1 = clamp(damage->y1, y_offset, y_end);
> +			y2 = clamp(damage->y2, y_offset, y_end);
> +		}
> +
> +		/*
> +		 * Clamp dirty rect to the valid FB range [y_offset, y_end].
> +		 * Per Bspec:
> +		 *   start_line >= y_offset
> +		 *   end_line <= y_offset + plane_height
> +		 */
> +		if (y1 != damage->y1 || y2 != damage->y2)
> +			drm_dbg_kms(display->drm,
> +				    "[PLANE:%d:%s] FBC dirty rect out of range: y1=%d y2=%d clamped to y1=%d y2=%d (y_offset=%d y_end=%d)\n",
> +				    plane->base.base.id, plane->base.name,
> +				    damage->y1, damage->y2, y1, y2, y_offset, y_end);

[Severity: Medium]
Will this warning trigger spuriously on almost every frame when the plane is
rotated 180 degrees?

For 180-degree planes, the code intentionally alters y1 and y2 to represent
inverted coordinates. The warning condition compares these new inverted
coordinates directly against the original, non-inverted coordinates.

Because an inverted coordinate will inherently mismatch a non-inverted one,
this condition evaluates to true on nearly every atomic update involving damage
for rotated planes.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812215350.3753102-1-austin.hu@intel.com?part=1

[PATCH 2/2] drm/i915/fbc: nuke CFB if Plane setting (except for surf addr) changes

[Austin Hu]

When FBC Dirty Rectangle mode is enabled, any non-PLANE_SURF register
update requires fetching the full plane frame buffer from memory to
re-compress and update the CFB in stolen memory.

Check plane state attributes during atomic commits and force a full
CFB nuke if any setting other than the surface address changes.

Signed-off-by: Austin Hu <austin.hu@intel.com>
---
 drivers/gpu/drm/i915/display/intel_fbc.c | 126 ++++++++++++++++++++++-
 1 file changed, 122 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
index c0fed695af0d..6bf5c0947671 100644
--- a/drivers/gpu/drm/i915/display/intel_fbc.c
+++ b/drivers/gpu/drm/i915/display/intel_fbc.c
@@ -1516,8 +1516,124 @@ static bool intel_fbc_is_ok(const struct intel_plane_state *plane_state)
 		intel_fbc_is_cfb_ok(plane_state);
 }
 
+/*
+ * From BSpec about "FBC Dirty Rectangle", when Dirty Rectangle mode is active,
+ * partial updates only apply to surface address changes. Any other plane state
+ * modification requires Plane to fetch full-plane pixel data from memory to
+ * re-compress and update the entire CFB in stolen memory. Once fully
+ * re-compressed, subsequent atomic commits go ahead with FBC dirty rectangle
+ * updates for smooth visual updates.
+ *
+ * So check any Plane attribute changed except for its surface address by
+ * referring to intel_async_flip_check_hw() which also checks async flip.
+ */
+static bool intel_fbc_dirty_rect_needs_nuke(struct intel_atomic_state *state,
+					    struct intel_plane *plane)
+{
+	struct intel_display *display = to_intel_display(state);
+	const struct intel_plane_state *old_plane_state =
+		intel_atomic_get_old_plane_state(state, plane);
+	const struct intel_plane_state *new_plane_state =
+		intel_atomic_get_new_plane_state(state, plane);
+
+	/*
+	 * If the plane state isn't part of this atomic transaction or during
+	 * initial plane setup, conservatively force a full CFB nuke.
+	 */
+	if (!old_plane_state || !new_plane_state)
+		return true;
+
+	if (old_plane_state->view.color_plane[0].mapping_stride !=
+	    new_plane_state->view.color_plane[0].mapping_stride) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Stride changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->hw.fb->modifier !=
+	    new_plane_state->hw.fb->modifier) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Modifier changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->hw.fb->format != new_plane_state->hw.fb->format) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Pixel format changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->hw.rotation != new_plane_state->hw.rotation) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Rotation changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (skl_plane_aux_dist(old_plane_state, 0) !=
+	    skl_plane_aux_dist(new_plane_state, 0)) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] AUX_DIST changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (!drm_rect_equals(&old_plane_state->uapi.src,
+			     &new_plane_state->uapi.src) ||
+	    !drm_rect_equals(&old_plane_state->uapi.dst,
+			     &new_plane_state->uapi.dst)) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Size/coords changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->hw.alpha != new_plane_state->hw.alpha) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Alpha changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->decrypt != new_plane_state->decrypt) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Decryption changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	/* Includes pixel_blend_mode, color_encoding & color_range checking. */
+	if (old_plane_state->color_ctl != new_plane_state->color_ctl) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Color ctl changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->cus_ctl != new_plane_state->cus_ctl) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] CUS ctl changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	if (old_plane_state->view.color_plane[0].x !=
+	    new_plane_state->view.color_plane[0].x) {
+		drm_dbg_kms(display->drm,
+			    "[PLANE:%d:%s] Color plane 0 x changed in FBC DIRTY RECT\n",
+			    plane->base.base.id, plane->base.name);
+		return true;
+	}
+
+	return false;
+}
+
 static void
-__intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
+__intel_fbc_prepare_dirty_rect(struct intel_atomic_state *state,
+			       const struct intel_plane_state *plane_state,
 			       const struct intel_crtc_state *crtc_state)
 {
 	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
@@ -1538,7 +1654,10 @@ __intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
 		return;
 	}
 
-	if (drm_rect_visible(damage)) {
+	if (intel_fbc_dirty_rect_needs_nuke(state, plane)) {
+		/* compress the entire region due to non PLANE_SURF updating. */
+		*fbc_dirty_rect = DRM_RECT_INIT(0, y_offset, width, height);
+	} else if (drm_rect_visible(damage)) {
 		int y1, y2;
 
 		if (plane_state->hw.rotation & DRM_MODE_ROTATE_180) {
@@ -1598,8 +1717,7 @@ intel_fbc_prepare_dirty_rect(struct intel_atomic_state *state,
 		mutex_lock(&fbc->lock);
 
 		if (fbc->state.plane == plane)
-			__intel_fbc_prepare_dirty_rect(plane_state,
-						       crtc_state);
+			__intel_fbc_prepare_dirty_rect(state, plane_state, crtc_state);
 
 		mutex_unlock(&fbc->lock);
 	}
-- 
2.34.1

Re: [PATCH 2/2] drm/i915/fbc: nuke CFB if Plane setting (except for surf addr) changes

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 2 potential issue(s) to consider:

New issues:
- [Medium] Strict equality check on `uapi.src` forces a full FBC CFB nuke on vertical panning (Y-offset changes), defeating dirty rectangle optimizations for scrolling.

Pre-existing issues:
- [High] Incorrect damage coordinate inversion math for 180-degree rotated planes results in 0-height dirty rectangles, freezing screen updates.
--

--- Patch [2]: [PATCH 2/2] drm/i915/fbc: nuke CFB if Plane setting (except for surf addr) changes ---
commit 50b0481138fde60ac48db330dd972dfba35b3f10
Author: Austin Hu <austin.hu@intel.com>

drm/i915/fbc: nuke CFB if Plane setting (except for surf addr) changes
    
When FBC Dirty Rectangle mode is enabled, any non-PLANE_SURF register
update requires fetching the full plane frame buffer from memory to
re-compress and update the CFB in stolen memory. This commit checks
plane state attributes during atomic commits and forces a full CFB
nuke if any setting other than the surface address changes.

> diff --git a/drivers/gpu/drm/i915/display/intel_fbc.c b/drivers/gpu/drm/i915/display/intel_fbc.c
> index c0fed695af0da..6bf5c09476713 100644
> --- a/drivers/gpu/drm/i915/display/intel_fbc.c
> +++ b/drivers/gpu/drm/i915/display/intel_fbc.c
> @@ -1516,8 +1516,124 @@ static bool intel_fbc_is_ok(const struct intel_plane_state *plane_state)
>  		intel_fbc_is_cfb_ok(plane_state);
>  }
>  
> +/*
> + * From BSpec about "FBC Dirty Rectangle", when Dirty Rectangle mode is active,

[ ... ]

> +static bool intel_fbc_dirty_rect_needs_nuke(struct intel_atomic_state *state,
> +					    struct intel_plane *plane)
> +{
> +	struct intel_display *display = to_intel_display(state);

[ ... ]

> +	if (skl_plane_aux_dist(old_plane_state, 0) !=
> +	    skl_plane_aux_dist(new_plane_state, 0)) {
> +		drm_dbg_kms(display->drm,
> +			    "[PLANE:%d:%s] AUX_DIST changed in FBC DIRTY RECT\n",
> +			    plane->base.base.id, plane->base.name);
> +		return true;
> +	}
> +
> +	if (!drm_rect_equals(&old_plane_state->uapi.src,
> +			     &new_plane_state->uapi.src) ||
> +	    !drm_rect_equals(&old_plane_state->uapi.dst,
> +			     &new_plane_state->uapi.dst)) {

[Severity: Medium]
Does this strict equality check on uapi.src accidentally force a full CFB
nuke during vertical panning?

A vertical pan (scrolling) changes uapi.src.y1 to shift the viewport, which
translates to a surface address update (PLANE_OFFSET / PLANE_SURF registers).
Because drm_rect_equals() checks the coordinates (x1 and y1), it fails when
panning, erroneously triggering a full CFB nuke on every frame of the scroll.

Should this perhaps verify drm_rect_width() and drm_rect_height() instead
to allow pure viewport shifts?

> +		drm_dbg_kms(display->drm,
> +			    "[PLANE:%d:%s] Size/coords changed in FBC DIRTY RECT\n",
> +			    plane->base.base.id, plane->base.name);
> +		return true;
> +	}
> +
> +	if (old_plane_state->hw.alpha != new_plane_state->hw.alpha) {

[ ... ]

>  static void
> -__intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
> +__intel_fbc_prepare_dirty_rect(struct intel_atomic_state *state,
> +			       const struct intel_plane_state *plane_state,
>  			       const struct intel_crtc_state *crtc_state)
>  {
>  	struct intel_plane *plane = to_intel_plane(plane_state->uapi.plane);
> @@ -1538,7 +1654,10 @@ __intel_fbc_prepare_dirty_rect(const struct intel_plane_state *plane_state,
>  		return;
>  	}
>  
> -	if (drm_rect_visible(damage)) {
> +	if (intel_fbc_dirty_rect_needs_nuke(state, plane)) {
> +		/* compress the entire region due to non PLANE_SURF updating. */
> +		*fbc_dirty_rect = DRM_RECT_INIT(0, y_offset, width, height);
> +	} else if (drm_rect_visible(damage)) {
>  		int y1, y2;
>  
>  		if (plane_state->hw.rotation & DRM_MODE_ROTATE_180) {
>  			/* Under 180 degree rotation, coordinate system is inverted */
>  			int inv_y1 = height - damage->y2;
>  			int inv_y2 = height - damage->y1;
>  
>  			y1 = clamp(y_offset + inv_y1, y_offset, y_end);
>  			y2 = clamp(y_offset + inv_y2, y_offset, y_end);

[Severity: High]
This is a pre-existing issue, but does this math incorrectly treat absolute
framebuffer coordinates as relative coordinates, resulting in zero-height
dirty rectangles for 180-degree rotated displays?

The damage clip is already in absolute framebuffer coordinates, meaning
damage->y2 resides between y_offset and y_end. Subtracting this from the
plane's height produces a value that, when added to y_offset, is almost
always less than y_offset. 

The clamp() function then pins both y1 and y2 strictly to y_offset,
programming a zero-height dirty rectangle and freezing screen updates on
rotated displays.

Could this be corrected to account for the absolute offset, perhaps using
something like y_end - (damage->y2 - y_offset)?

>  		} else {
>  			y1 = clamp(damage->y1, y_offset, y_end);
>  			y2 = clamp(damage->y2, y_offset, y_end);

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260812215350.3753102-1-austin.hu@intel.com?part=2

✗ i915.CI.BAT: failure for drm/i915/fbc: Dirty rectangle bounds enforcement and CFB nuke handling

[Patchwork]

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== Series Details ==

Series: drm/i915/fbc: Dirty rectangle bounds enforcement and CFB nuke handling
URL   : https://patchwork.freedesktop.org/series/172104/
State : failure

== Summary ==

CI Bug Log - changes from CI_DRM_18985 -> Patchwork_172104v1
====================================================

Summary
-------

  **FAILURE**

  Serious unknown changes coming with Patchwork_172104v1 absolutely need to be
  verified manually.
  
  If you think the reported changes have nothing to do with the changes
  introduced in Patchwork_172104v1, please notify your bug team (I915-ci-infra@lists.freedesktop.org) to allow them
  to document this new failure mode, which will reduce false positives in CI.

  External URL: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_172104v1/index.html

Participating hosts (37 -> 34)
------------------------------

  Missing    (3): bat-dg2-13 bat-rpls-4 fi-snb-2520m 

Possible new issues
-------------------

  Here are the unknown changes that may have been introduced in Patchwork_172104v1:

### IGT changes ###

#### Possible regressions ####

  * igt@i915_module_load@load:
    - fi-bsw-n3050:       [PASS][1] -> [DMESG-WARN][2]
   [1]: https://intel-gfx-ci.01.org/tree/drm-tip/CI_DRM_18985/fi-bsw-n3050/igt@i915_module_load@load.html
   [2]: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_172104v1/fi-bsw-n3050/igt@i915_module_load@load.html

  


Build changes
-------------

  * Linux: CI_DRM_18985 -> Patchwork_172104v1

  CI-20190529: 20190529
  CI_DRM_18985: 707b81710802330f08e561e54d174f74abdb10e5 @ git://anongit.freedesktop.org/gfx-ci/linux
  IGT_9054: 3d819a8f511b2bcd844647bcf7e433b9407d058e @ https://gitlab.freedesktop.org/drm/igt-gpu-tools.git
  Patchwork_172104v1: 707b81710802330f08e561e54d174f74abdb10e5 @ git://anongit.freedesktop.org/gfx-ci/linux

== Logs ==

For more details see: https://intel-gfx-ci.01.org/tree/drm-tip/Patchwork_172104v1/index.html

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