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Date: Thu, 27 Jul 2023 16:25:00 +0900
From: Tomasz Figa <tfiga@...omium.org>
To: Hsia-Jun Li <Randy.Li@...aptics.com>
Cc: linux-media@...r.kernel.org, ayaka@...lik.info,
hans.verkuil@...co.com, mchehab@...nel.org,
laurent.pinchart@...asonboard.com, hiroh@...omium.org,
hverkuil@...all.nl, linux-kernel@...r.kernel.org,
nicolas@...fresne.ca
Subject: Re: [PATCH 2/2] media: v4l2-mem2mem: add a list for buf used by hw
On Mon, Jul 17, 2023 at 4:15 PM Hsia-Jun Li <Randy.Li@...aptics.com> wrote:
>
>
> On 7/12/23 17:33, Tomasz Figa wrote:
> > CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
> >
> >
> > On Tue, Jul 04, 2023 at 12:00:38PM +0800, Hsia-Jun Li wrote:
> >> From: "Hsia-Jun(Randy) Li" <randy.li@...aptics.com>
> >>
> >> Many drivers have to create its own buf_struct for a
> >> vb2_queue to track such a state. Also driver has to
> >> iterate over rdy_queue every times to find out a buffer
> >> which is not sent to hardware(or firmware), this new
> >> list just offers the driver a place to store the buffer
> >> that hardware(firmware) has acknowledged.
> >>
> >> One important advance about this list, it doesn't like
> >> rdy_queue which both bottom half of the user calling
> >> could operate it, while the v4l2 worker would as well.
> >> The v4l2 core could only operate this queue when its
> >> v4l2_context is not running, the driver would only
> >> access this new hw_queue in its own worker.
> > Could you describe in what case such a list would be useful for a
> > mem2mem driver?
>
> This list, as its description, just for saving us from creating a
> private buffer struct to track buffer state.
>
> The queue in the kernel is not the queue that hardware(codec firmware)
> are using.
>
Sorry, I find the description difficult to understand. It might make
sense to have the text proofread by someone experienced in writing
technical documentation in English before posting in the future.
Thanks.
I think I got the point from Nicolas' explanation, though.
>
> >> Signed-off-by: Hsia-Jun(Randy) Li <randy.li@...aptics.com>
> >> ---
> >> drivers/media/v4l2-core/v4l2-mem2mem.c | 25 +++++++++++++++++--------
> >> include/media/v4l2-mem2mem.h | 10 +++++++++-
> >> 2 files changed, 26 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/drivers/media/v4l2-core/v4l2-mem2mem.c b/drivers/media/v4l2-core/v4l2-mem2mem.c
> >> index c771aba42015..b4151147d5bd 100644
> >> --- a/drivers/media/v4l2-core/v4l2-mem2mem.c
> >> +++ b/drivers/media/v4l2-core/v4l2-mem2mem.c
> >> @@ -321,15 +321,21 @@ static void __v4l2_m2m_try_queue(struct v4l2_m2m_dev *m2m_dev,
> >> goto job_unlock;
> >> }
> >>
> >> - src = v4l2_m2m_next_src_buf(m2m_ctx);
> >> - dst = v4l2_m2m_next_dst_buf(m2m_ctx);
> >> - if (!src && !m2m_ctx->out_q_ctx.buffered) {
> >> - dprintk("No input buffers available\n");
> >> - goto job_unlock;
> >> + if (list_empty(&m2m_ctx->out_q_ctx.hw_queue)) {
> >> + src = v4l2_m2m_next_src_buf(m2m_ctx);
> >> +
> >> + if (!src && !m2m_ctx->out_q_ctx.buffered) {
> >> + dprintk("No input buffers available\n");
> >> + goto job_unlock;
> >> + }
> >> }
> >> - if (!dst && !m2m_ctx->cap_q_ctx.buffered) {
> >> - dprintk("No output buffers available\n");
> >> - goto job_unlock;
> >> +
> >> + if (list_empty(&m2m_ctx->cap_q_ctx.hw_queue)) {
> >> + dst = v4l2_m2m_next_dst_buf(m2m_ctx);
> >> + if (!dst && !m2m_ctx->cap_q_ctx.buffered) {
> >> + dprintk("No output buffers available\n");
> >> + goto job_unlock;
> >> + }
> >> }
> > src and dst would be referenced unitialized below if neither of the
> > above ifs hits...
> I think they have been initialized at v4l2_m2m_ctx_init()
What do you mean? They are local variables in this function.
> >
> > Best regards,
> > Tomasz
> >
> >> m2m_ctx->new_frame = true;
> >> @@ -896,6 +902,7 @@ int v4l2_m2m_streamoff(struct file *file, struct v4l2_m2m_ctx *m2m_ctx,
> >> INIT_LIST_HEAD(&q_ctx->rdy_queue);
> >> q_ctx->num_rdy = 0;
> >> spin_unlock_irqrestore(&q_ctx->rdy_spinlock, flags);
> >> + INIT_LIST_HEAD(&q_ctx->hw_queue);
> >>
> >> if (m2m_dev->curr_ctx == m2m_ctx) {
> >> m2m_dev->curr_ctx = NULL;
> >> @@ -1234,6 +1241,8 @@ struct v4l2_m2m_ctx *v4l2_m2m_ctx_init(struct v4l2_m2m_dev *m2m_dev,
> >>
> >> INIT_LIST_HEAD(&out_q_ctx->rdy_queue);
> >> INIT_LIST_HEAD(&cap_q_ctx->rdy_queue);
> >> + INIT_LIST_HEAD(&out_q_ctx->hw_queue);
> >> + INIT_LIST_HEAD(&cap_q_ctx->hw_queue);
> >> spin_lock_init(&out_q_ctx->rdy_spinlock);
> >> spin_lock_init(&cap_q_ctx->rdy_spinlock);
> >>
> >> diff --git a/include/media/v4l2-mem2mem.h b/include/media/v4l2-mem2mem.h
> >> index d6c8eb2b5201..2342656e582d 100644
> >> --- a/include/media/v4l2-mem2mem.h
> >> +++ b/include/media/v4l2-mem2mem.h
> >> @@ -53,9 +53,16 @@ struct v4l2_m2m_dev;
> >> * processed
> >> *
> >> * @q: pointer to struct &vb2_queue
> >> - * @rdy_queue: List of V4L2 mem-to-mem queues
> >> + * @rdy_queue: List of V4L2 mem-to-mem queues. If v4l2_m2m_buf_queue() is
> >> + * called in struct vb2_ops->buf_queue(), the buffer enqueued
> >> + * by user would be added to this list.
> >> * @rdy_spinlock: spin lock to protect the struct usage
> >> * @num_rdy: number of buffers ready to be processed
> >> + * @hw_queue: A list for tracking the buffer is occupied by the hardware
> >> + * (or device's firmware). A buffer could only be in either
> >> + * this list or @rdy_queue.
> >> + * Driver may choose not to use this list while uses its own
> >> + * private data to do this work.
> >> * @buffered: is the queue buffered?
> >> *
> >> * Queue for buffers ready to be processed as soon as this
> >> @@ -68,6 +75,7 @@ struct v4l2_m2m_queue_ctx {
> >> struct list_head rdy_queue;
> >> spinlock_t rdy_spinlock;
> >> u8 num_rdy;
> >> + struct list_head hw_queue;
> >> bool buffered;
> >> };
> >>
> >> --
> >> 2.17.1
> >>
> --
> Hsia-Jun(Randy) Li
>
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