Re: [PATCH v4 10/10] usb: gadget: uvc: add min g_ctrl vidioc and set min buffs to 4

Laurent Pinchart
2024-08-13T09:35:50Z

On Tue, Aug 13, 2024 at 11:09:34AM +0200, Michael Grzeschik wrote:
> We increase the minimum amount of v4l2 buffers that will be possibly
> enqueued into the hardware and allocate at least
> UVCG_STREAMING_MIN_BUFFERS amount of requests. This way the driver has
> also more requests available to prefill the isoc hardware with.
>
> Signed-off-by: Michael Grzeschik <m.grzeschik@pengutronix.de>
>
> ---
> v3 -> v4: -
> v1 -> v3: new patch
> ---
> drivers/usb/gadget/function/uvc.h | 2 ++
> drivers/usb/gadget/function/uvc_queue.c | 3 ++-
> drivers/usb/gadget/function/uvc_v4l2.c | 13 +++++++++++++
> 3 files changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/gadget/function/uvc.h b/drivers/usb/gadget/function/uvc.h
> index f6bc58fb02b84..e0b1f78fdbc65 100644
> --- a/drivers/usb/gadget/function/uvc.h
> +++ b/drivers/usb/gadget/function/uvc.h
> @@ -71,6 +71,8 @@ extern unsigned int uvc_gadget_trace_param;
>
> #define UVCG_REQUEST_HEADER_LEN 12
>
> +#define UVCG_STREAMING_MIN_BUFFERS 4
> +

4 is a large number that drastically increases latency.

> /* ------------------------------------------------------------------------
> * Structures
> */
> diff --git a/drivers/usb/gadget/function/uvc_queue.c b/drivers/usb/gadget/function/uvc_queue.c
> index e33ce72325031..157e7f7d49c7a 100644
> --- a/drivers/usb/gadget/function/uvc_queue.c
> +++ b/drivers/usb/gadget/function/uvc_queue.c
> @@ -21,6 +21,7 @@
> #include <media/videobuf2-vmalloc.h>
>
> #include "uvc.h"
> +#include "uvc_video.h"
>
> /* ------------------------------------------------------------------------
> * Video buffers queue management.
> @@ -86,7 +87,7 @@ static int uvc_queue_setup(struct vb2_queue *vq,
> }
>
> video->req_size = req_size;
> - video->uvc_num_requests = nreq;
> + video->uvc_num_requests = nreq * UVCG_STREAMING_MIN_BUFFERS;
>
> return 0;
> }
> diff --git a/drivers/usb/gadget/function/uvc_v4l2.c b/drivers/usb/gadget/function/uvc_v4l2.c
> index 392fb400aad14..f96074f2c2824 100644
> --- a/drivers/usb/gadget/function/uvc_v4l2.c
> +++ b/drivers/usb/gadget/function/uvc_v4l2.c
> @@ -357,6 +357,18 @@ static int uvc_v4l2_s_parm(struct file *file, void *fh,
> return 0;
> }
>
> +static int uvc_g_ctrl(struct file *file, void *priv, struct v4l2_control *vc)
> +{
> + int ret = -EINVAL;
> +
> + if (vc->id == V4L2_CID_MIN_BUFFERS_FOR_OUTPUT) {
> + vc->value = UVCG_STREAMING_MIN_BUFFERS;
> + ret = 0;
> + }
> +
> + return ret;
> +}
> +
> static int
> uvc_v4l2_enum_frameintervals(struct file *file, void *fh,
> struct v4l2_frmivalenum *fival)
> @@ -629,6 +641,7 @@ const struct v4l2_ioctl_ops uvc_v4l2_ioctl_ops = {
> .vidioc_streamoff = uvc_v4l2_streamoff,
> .vidioc_s_parm = uvc_v4l2_s_parm,
> .vidioc_g_parm = uvc_v4l2_g_parm,
> + .vidioc_g_ctrl = uvc_g_ctrl,
> .vidioc_subscribe_event = uvc_v4l2_subscribe_event,
> .vidioc_unsubscribe_event = uvc_v4l2_unsubscribe_event,
> .vidioc_default = uvc_v4l2_ioctl_default,

--
Regards,

Laurent Pinchart