[PATCH v2] media: iris: use fallback size when S_FMT is called without width/height

[Val Packett <val@packett.cool>]

According to 4.5.1.5 of the M2M stateful decoder UAPI documentation,
providing the width and the height to S_FMT is "required only if it
cannot be parsed from the stream", otherwise they can be left as 0
and the S_FMT implementation is expected to return a valid placeholder
resolution that would let REQBUFS succeed.

iris was missing the fallback, so clients like rpi-ffmpeg wouldn't work.
Fix by adding an explicit fallback to defaults.

Fixes: b530b95de22c ("media: iris: implement s_fmt, g_fmt and try_fmt ioctls")
Link: https://github.com/jc-kynesim/rpi-ffmpeg/issues/103
Reviewed-by: Dikshita Agarwal <dikshita.agarwal@oss.qualcomm.com>
Signed-off-by: Val Packett <val@packett.cool>
---
v2:
  - Added small comment as requested
  - Pulled an R-b (that depended on the comment)
  - Slightly reworded commit message
v1: https://lore.kernel.org/all/20251012235330.20897-1-val@packett.cool/

 drivers/media/platform/qcom/iris/iris_vdec.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/media/platform/qcom/iris/iris_vdec.c b/drivers/media/platform/qcom/iris/iris_vdec.c
index 69ffe52590d3..227e4e5a326f 100644
--- a/drivers/media/platform/qcom/iris/iris_vdec.c
+++ b/drivers/media/platform/qcom/iris/iris_vdec.c
@@ -231,6 +231,14 @@ int iris_vdec_s_fmt(struct iris_inst *inst, struct v4l2_format *f)
 	if (vb2_is_busy(q))
 		return -EBUSY;
 
+	/* Width and height are optional, so fall back to a valid placeholder
+	 * resolution until the real one is decoded from the bitstream.
+	 */
+	if (f->fmt.pix_mp.width == 0 && f->fmt.pix_mp.height == 0) {
+		f->fmt.pix_mp.width = DEFAULT_WIDTH;
+		f->fmt.pix_mp.height = DEFAULT_HEIGHT;
+	}
+
 	iris_vdec_try_fmt(inst, f);
 
 	switch (f->type) {
-- 
2.51.2