[PATCH v2] media: v4l2-ctrls: default HEVC SPS chroma format to 4:2:0

[Tharit Tangkijwanichakul <tharitt97@gmail.com>]

The default value of a compound control is zero initialized when no
explicit default is provided. For V4L2_CTRL_TYPE_HEVC_SPS this results
in chroma_format_idc being set to 0, which represents monochrome video.

Most stateless HEVC decoders do not support monochrome video. In
particular, the VDPU38x variant of rkvdec fails v4l2-compliance in two
tests related to V4L2_CID_STATELESS_HEVC_SPS.  The Control ioctls test
reads the control with GET_EXT_CTRLS and writes the same value
back; TRY_EXT_CTRLS then returns -EINVAL because the VDPU38x
rkvdec_hevc_validate_sps() rejects sps->chroma_format_idc == 0.

    v4l2-compliance 1.33.0-5491, 64 bits, 64-bit time_t
    v4l2-compliance SHA: b32589c51481 2026-07-16 08:51:38
    Control ioctls:
        fail: v4l2-test-controls.cpp(942):
	try_ext_ctrls returned an error (22)
      test VIDIOC_G/S/TRY_EXT_CTRLS: FAIL
    Buffer ioctls:
        fail: v4l2-test-buffers.cpp(3102): node->streamon(q.g_type())
        fail: v4l2-test-buffers.cpp(3157): testBlockingDQBuf(node, m2m_q)
      test blocking wait: FAIL

Set the common HEVC SPS compound control default to
chroma_format_idc = 1, corresponding to 4:2:0.

Fixes: c9a59dc2acc7 ("media: rkvdec: Add HEVC support for the VDPU381 variant")
Signed-off-by: Tharit Tangkijwanichakul <tharitt97@gmail.com>
---
Changes in v2:
- Move the HEVC SPS default from rkvdec to the common V4L2 control core,
  as suggested by Nicolas Dufresne.
- Default V4L2_CTRL_TYPE_HEVC_SPS chroma_format_idc to 1 (4:2:0).

 drivers/media/v4l2-core/v4l2-ctrls-core.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/media/v4l2-core/v4l2-ctrls-core.c b/drivers/media/v4l2-core/v4l2-ctrls-core.c
index ba047d7d8601..d7adf334a0ad 100644
--- a/drivers/media/v4l2-core/v4l2-ctrls-core.c
+++ b/drivers/media/v4l2-core/v4l2-ctrls-core.c
@@ -112,6 +112,7 @@ static void std_init_compound(const struct v4l2_ctrl *ctrl, u32 idx,
 	struct v4l2_ctrl_fwht_params *p_fwht_params;
 	struct v4l2_ctrl_h264_scaling_matrix *p_h264_scaling_matrix;
 	struct v4l2_ctrl_av1_sequence *p_av1_sequence;
+	struct v4l2_ctrl_hevc_sps *p_hevc_sps;
 	void *p = ptr.p + idx * ctrl->elem_size;
 
 	if (ctrl->p_def.p_const)
@@ -185,6 +186,12 @@ static void std_init_compound(const struct v4l2_ctrl *ctrl, u32 idx,
 		 */
 		memset(p_h264_scaling_matrix, 16, sizeof(*p_h264_scaling_matrix));
 		break;
+	case V4L2_CTRL_TYPE_HEVC_SPS:
+		p_hevc_sps = p;
+
+		/* 4:2:0 */
+		p_hevc_sps->chroma_format_idc = 1;
+		break;
 	}
 }
 
-- 
2.47.3