[RFC PATCH 1/5] media: iris: Don't flag an empty source change LAST buffer as an error

[Christian Cortner <ccortner@gmail.com>]

When the firmware completes a source change, it returns the last capture
buffer from before the change flagged HFI_BUF_FW_FLAG_PSC_LAST, and that
buffer can be empty. iris_hfi_gen2_handle_output_buffer() sets
V4L2_BUF_FLAG_ERROR on every empty capture buffer returned while
streaming unless it carries HFI_BUF_FW_FLAG_LAST, the flag that ends a
drain, so the empty buffer that ends a source change reaches the client
flagged both LAST and ERROR.

The stateful decoder interface says of this buffer, as it does of the
one that ends a drain, that it "may be empty (with v4l2_buffer bytesused
= 0) and in that case it must be ignored by the client, as it does not
contain a decoded frame". With the ERROR flag, ffmpeg's h264_v4l2m2m
decoder reports "capture: driver decode error" and outputs a corrupted
frame.

Exempt HFI_BUF_FW_FLAG_PSC_LAST as well.

Fixes: 7adc11e6abf6 ("media: iris: Send V4L2_BUF_FLAG_ERROR for capture buffers with 0 filled length")
Cc: stable@vger.kernel.org
Assisted-by: LLM sparse smatch
---
Reference only, not for merging (no Signed-off-by); see the cover
letter.

 drivers/media/platform/qcom/iris/iris_hfi_gen2_response.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/media/platform/qcom/iris/iris_hfi_gen2_response.c b/drivers/media/platform/qcom/iris/iris_hfi_gen2_response.c
index f0782c4b1e6e..b4fe9066fcb8 100644
--- a/drivers/media/platform/qcom/iris/iris_hfi_gen2_response.c
+++ b/drivers/media/platform/qcom/iris/iris_hfi_gen2_response.c
@@ -390,8 +390,13 @@ static int iris_hfi_gen2_handle_output_buffer(struct iris_inst *inst,
 
 	buf->flags = iris_hfi_gen2_get_driver_buffer_flags(inst, hfi_buffer->flags);
 
+	/*
+	 * The empty buffer that ends a drain (LAST) or a source change
+	 * (PSC_LAST) is not an error, the client just ignores it.
+	 */
 	if (!buf->data_size && inst->state == IRIS_INST_STREAMING &&
-	    !(hfi_buffer->flags & HFI_BUF_FW_FLAG_LAST)) {
+	    !(hfi_buffer->flags &
+	      (HFI_BUF_FW_FLAG_LAST | HFI_BUF_FW_FLAG_PSC_LAST))) {
 		buf->flags |= V4L2_BUF_FLAG_ERROR;
 	}
 
-- 
2.56.0