From: Vidya Srinivas Date: Thu, 18 Jun 2026 18:18:37 +0000 (+0530) Subject: drm/i915/display: Fix NV12 ceiling division for bigjoiner case X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f61289af2667a942f48859fe0b030894153ad1d2;p=thirdparty%2Fkernel%2Flinux.git drm/i915/display: Fix NV12 ceiling division for bigjoiner case Commit 16df4cc63c58 ("drm/i915/display: Use ceiling division for NV12 UV surface offset calculation") computes the UV (chroma) surface start/size as ceiling(half of Y plane start/size) directly from the U16.16 fixed-point source rectangle: x = fp_16_16_to_int_ceil(fp_16_16_div2(src.x1)); For a single pipe the source coordinates are integers, so this is correct. (UV start = ceiling(half of Y plane start)). With bigjoiner + a plane scaler the picture changes. The pipe boundary is a fixed integer destination pixel, but the plane's position and the scaler ratio are arbitrary, so drm_rect_clip_scaled() maps the seam back to a *fractional* per-pipe source. For a 1280->2407 upscaled NV12 plane crossing the seam: master src: width = 1204 * 1280/2407 = 640.265899, x1 = 0 joiner src: width = 1203 * 1280/2407 = 639.734115, x1 = 640.265884 The luma path floors this to an integer (src.x1 >> 16 = 640), but the UV path takes ceiling(640.265884 / 2) = ceil(320.13) = 321. The Y plane then starts at column 640 while the UV plane starts at 321*2 = 642, pushing the chroma read one column past the 640-wide chroma surface on the joiner secondary: [CRTC:382:pipe C] PLANE ATS fault [CRTC:382:pipe C][PLANE:267:plane 1C] fault (CTL=0x81009400, ...) The spec "Y plane start" is the integer pixel the luma surface actually programs (640), not the pre-floor fixed-point value (640.27). Convert the Y plane start/size to integer first - matching skl_check_main_surface() - and then apply the ceiling. This is a no-op for the integer (non-joiner) case and yields the correct, in-bounds chroma offset for the fractional joiner seam: before fix after fix master 1B: x=0 w=321 x=0 w=320 -> [0, 320) slave 1C: x=321 w=320 x=320 w=320 -> [320, 640) The two halves now tile the 640-wide chroma plane exactly and the ATS fault is gone. Assisted-by: GitHub-Copilot:Claude-Opus-4.8 Fixes: 16df4cc63c58 ("drm/i915/display: Use ceiling division for NV12 UV surface offset calculation") Signed-off-by: Vidya Srinivas Reviewed-by: Juha-Pekka Heikkila Signed-off-by: Uma Shankar Link: https://patch.msgid.link/20260618181837.687302-1-vidya.srinivas@intel.com (cherry picked from commit 0c59cc78241c10e5f02d92b28d811b0435e706a7) Signed-off-by: Rodrigo Vivi --- diff --git a/drivers/gpu/drm/i915/display/skl_universal_plane.c b/drivers/gpu/drm/i915/display/skl_universal_plane.c index ad4bfff6903d..164b7d61c9a3 100644 --- a/drivers/gpu/drm/i915/display/skl_universal_plane.c +++ b/drivers/gpu/drm/i915/display/skl_universal_plane.c @@ -2126,19 +2126,6 @@ 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); @@ -2154,14 +2141,20 @@ static int skl_check_nv12_aux_surface(struct intel_plane_state *plane_state) int max_height = intel_plane_max_height(plane, fb, uv_plane, rotation); /* - * LNL+ UV surface start/size = - * ceiling(half of Y plane start/size). Use ceiling division - * unconditionally; it is a no-op for even values. + * UV (chroma) start/size = ceiling(half of the *integer* Y plane + * start/size), i.e. the value the luma surface programs (src >> 16), + * not the raw U16.16. A bigjoiner seam mapped through the scaler can + * give a fractional luma src; ceiling that directly would round the + * chroma one column too far and read past the chroma surface. */ - 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))); + int luma_x = plane_state->uapi.src.x1 >> 16; + int luma_y = plane_state->uapi.src.y1 >> 16; + int luma_w = drm_rect_width(&plane_state->uapi.src) >> 16; + int luma_h = drm_rect_height(&plane_state->uapi.src) >> 16; + int x = DIV_ROUND_UP(luma_x, 2); + int y = DIV_ROUND_UP(luma_y, 2); + int w = DIV_ROUND_UP(luma_x + luma_w, 2) - x; + int h = DIV_ROUND_UP(luma_y + luma_h, 2) - y; u32 offset; /* FIXME not quite sure how/if these apply to the chroma plane */