[PATCH 2/9] media: iris: account for UBWC extradata in the QC08C buffer size

[Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>]

iris_yuv_buffer_size_qc08c() sums only the luma/chroma data and metadata
planes. The UBWC engine additionally writes a trailing extradata/scratch
region below the frame, so the computed size is too small for the
reconstruction (DPB) buffer. When the firmware writes that trailing region
it overruns the buffer and triggers an IOMMU fault; this is hit when
decoding interlaced content, where the reconstruction buffers are packed
with a gap after each buffer.

Add the trailing region to the buffer size, sized as the venus driver does
(max of 16K and 48 luma lines).

Fixes: cfd71b14b0d6 ("media: iris: Add support for QC08C format for decoder")
Assisted-by: Claude:claude-opus-4-8
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/media/platform/qcom/iris/iris_buffer.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/qcom/iris/iris_buffer.c b/drivers/media/platform/qcom/iris/iris_buffer.c
index 246ad0abbac3..f1de4442be1f 100644
--- a/drivers/media/platform/qcom/iris/iris_buffer.c
+++ b/drivers/media/platform/qcom/iris/iris_buffer.c
@@ -261,7 +261,8 @@ static u32 iris_yuv_buffer_size_qc08c(struct iris_inst *inst)
 	uv_plane = ALIGN(uv_stride * ALIGN(f->fmt.pix_mp.height / 2, UV_SCANLINE_ALIGN_QC08C),
 			 PIXELS_4K);
 
-	return ALIGN(y_meta_plane + y_plane + uv_meta_plane + uv_plane, PIXELS_4K);
+	return ALIGN(y_meta_plane + y_plane + uv_meta_plane + uv_plane +
+		     max_t(u32, SZ_16K, y_stride * 48), PIXELS_4K);
 }
 
 /*

-- 
2.47.3