[media] coda: try to only queue a single JPEG into the bitstream

With bitstream padding, it is possible to decode a single JPEG in the bitstream
immediately. This allows us to only ever queue a single JPEG into the bitstream
buffer, except to increase payload over 512 bytes or to back out of hold state.
This is a measure to decrease JPEG decoder latency.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/platform/coda/coda-bit.c

@@ -221,6 +221,14 @@ void coda_fill_bitstream(struct coda_ctx *ctx)
 	u32 start;
 
 	while (v4l2_m2m_num_src_bufs_ready(ctx->fh.m2m_ctx) > 0) {
+		/*
+		 * Only queue a single JPEG into the bitstream buffer, except
+		 * to increase payload over 512 bytes or if in hold state.
+		 */
+		if (ctx->codec->src_fourcc == V4L2_PIX_FMT_JPEG &&
+		    (coda_get_bitstream_payload(ctx) >= 512) && !ctx->hold)
+			break;
+
 		src_buf = v4l2_m2m_next_src_buf(ctx->fh.m2m_ctx);
 
 		/* Buffer start position */