Hi,
On 29/09/2022 09:48, Bingbu Cao wrote:
On 8/31/22 10:13 PM, Tomi Valkeinen wrote:
V4L2_FRAME_DESC_ENTRY_MAX is currently set to 4. In theory it's possible
to have an arbitrary amount of streams in a single pad, so preferably
there should be no hardcoded maximum number.
However, I believe a reasonable max is 8, which would cover a CSI-2 pad
with 4 streams of pixel data and 4 streams of metadata.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@xxxxxxxxxxxxxxxx>
Reviewed-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
Reviewed-by: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
Reviewed-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
---
include/media/v4l2-subdev.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/media/v4l2-subdev.h b/include/media/v4l2-subdev.h
index 9689f38a0af1..3797b99bb408 100644
--- a/include/media/v4l2-subdev.h
+++ b/include/media/v4l2-subdev.h
@@ -358,7 +358,11 @@ struct v4l2_mbus_frame_desc_entry {
} bus;
};
-#define V4L2_FRAME_DESC_ENTRY_MAX 4
+ /*
+ * If this number is too small, it should be dropped altogether and the
+ * API switched to a dynamic number of frame descriptor entries.
+ */
+#define V4L2_FRAME_DESC_ENTRY_MAX 8
The number 8 here is still not enough I think, CSI2 specification already
extended the VC identifier to be at most 5 bits, which support a max of
32 VCs.
Well, 8 frame desc entries is not enough for the "old" CSI2 either as
there can be a lot of data-types, each a separate stream ("stream" as
defined by this series) which needs a frame desc.
Considering the metadata, the number should be larger, it looks like that
we have to switch using dynamic number?
Do we have a current use case which needs more than 8 streams per pad?
If not, I'd stay away from this for the time being. This can be changed
later.
BTW, does this change break the uAPI?
No, the frame desc is fully internal to the kernel.
Tomi
