From: Vidya Srinivas Date: Wed, 15 Apr 2026 16:58:49 +0000 (+0530) Subject: drm/i915/display: Use ceiling division for NV12 UV surface offset calculation X-Git-Url: http://git.ipfire.org/gitweb/index.cgi?a=commitdiff_plain;h=16df4cc63c58b6ae4dc794edcc2661c5dddc3596;p=thirdparty%2Fkernel%2Flinux.git drm/i915/display: Use ceiling division for NV12 UV surface offset calculation For LNL+, odd source size and panning for YUV 422/420 surfaces is supported. However, it requires the UV (chroma) surface Start X/Y and width/height to be calculated as ceiling(half of Y plane value) rather than floor. The current code uses (>> 17) which combines the U16.16 fixed-point to integer conversion (>> 16) with a divide-by-2 for chroma subsampling (>> 1) into a single floor division. For odd Y plane values this produces an off-by-one error in the UV plane offset. On Android systems we see PLANE ATS fault when NV12 overlays are used with odd source dimensions: [ 126.854200] xe 0000:00:02.0: [drm:intel_atomic_setup_scaler [xe]] [CRTC:148:pipe A] attached scaler id 0.0 to PLANE:33 [ 126.854617] xe 0000:00:02.0: [drm:skl_update_scaler [xe]] [CRTC:148:pipe A] scaler_user index 0.0: staged scaling request for 1279x719->1340x753 [ 126.854837] xe 0000:00:02.0: [drm:intel_plane_atomic_check [xe]] UV plane [PLANE:33:plane 1A] using Y plane [PLANE:123:plane 4A] [ 126.854926] xe 0000:00:02.0: [drm] *ERROR* [CRTC:148:pipe A] PLANE ATS fault With Y plane width 1279: floor(1279/2) = 639 (current) ceil(1279/2) = 640 (required) Introduce fp_16_16_div2() and fp_16_16_to_int_ceil() helpers to cleanly separate the two operations: first halve the U16.16 fixed-point value for chroma subsampling (staying in fixed-point domain), then convert to integer with ceiling rounding. v2: Use DIV_ROUND_UP(value, 1 << 17) to preserve sub-pixel precision while making the ceiling division readable (Jani, Uma) v3: Split into two helpers - fp_16_16_div2() for fixed-point division by 2 and fp_16_16_to_int_ceil() for ceiling conversion to integer, cleanly separating chroma subsampling from fixed-point to integer conversion (Jani) Signed-off-by: Vidya Srinivas Reviewed-by: Juha-Pekka Heikkila Signed-off-by: Mika Kahola Link: https://patch.msgid.link/20260415165849.187693-1-vidya.srinivas@intel.com --- diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c index 5aef8123d8b8f..ef431dd32e74a 100644 --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c @@ -2126,6 +2126,19 @@ static int skl_check_main_surface(struct intel_plane_state *plane_state) return 0; } + +/* Divide a U16.16 fixed-point value by 2, staying in fixed-point domain */ +static inline u32 fp_16_16_div2(u32 fp) +{ + return fp >> 1; +} + +/* Convert a U16.16 fixed-point value to integer, rounding up */ +static inline int fp_16_16_to_int_ceil(u32 fp) +{ + return DIV_ROUND_UP(fp, 1 << 16); +} + static int skl_check_nv12_aux_surface(struct intel_plane_state *plane_state) { struct intel_display *display = to_intel_display(plane_state); @@ -2139,10 +2152,16 @@ static int skl_check_nv12_aux_surface(struct intel_plane_state *plane_state) int min_height = intel_plane_min_height(plane, fb, uv_plane, rotation); int max_width = intel_plane_max_width(plane, fb, uv_plane, rotation); int max_height = intel_plane_max_height(plane, fb, uv_plane, rotation); - int x = plane_state->uapi.src.x1 >> 17; - int y = plane_state->uapi.src.y1 >> 17; - int w = drm_rect_width(&plane_state->uapi.src) >> 17; - int h = drm_rect_height(&plane_state->uapi.src) >> 17; + + /* + * LNL+ UV surface start/size = + * ceiling(half of Y plane start/size). Use ceiling division + * unconditionally; it is a no-op for even values. + */ + int x = fp_16_16_to_int_ceil(fp_16_16_div2(plane_state->uapi.src.x1)); + int y = fp_16_16_to_int_ceil(fp_16_16_div2(plane_state->uapi.src.y1)); + int w = fp_16_16_to_int_ceil(fp_16_16_div2(drm_rect_width(&plane_state->uapi.src))); + int h = fp_16_16_to_int_ceil(fp_16_16_div2(drm_rect_height(&plane_state->uapi.src))); u32 offset; /* FIXME not quite sure how/if these apply to the chroma plane */