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Date: Tue, 18 Jul 2023 11:53:25 +0800
From: Hsia-Jun Li <Randy.Li@...aptics.com>
To: Nicolas Dufresne <nicolas@...fresne.ca>
Cc: linux-media@...r.kernel.org, Tomasz Figa <tfiga@...omium.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
Subject: Re: [PATCH 2/2] media: v4l2-mem2mem: add a list for buf used by hw
On 7/17/23 22:07, Nicolas Dufresne wrote:
> CAUTION: Email originated externally, do not click links or open attachments unless you recognize the sender and know the content is safe.
>
>
> Le mercredi 12 juillet 2023 à 09:33 +0000, Tomasz Figa a écrit :
>> 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?
> Today all driver must track buffers that are "owned by the hardware". This is a
> concept dictated by the m2m framework and enforced through the ACTIVE flag.
I think that flag is confusing, the m2m framework would only set this
flag when a buffer is enqueue into v4l2 (__enqueue_in_driver()).
The application can't know whether the driver(or hardware) would still
use it when that buffer is dequeued(__vb2_dqbuf() would override the
state here).
I was trying to suggest a flag for the new DELETE_BUF ioctl() or it
could delete a buffer which the hardware could still use in the future,
if we are not in the case for non-secure stateless codec.
> All
> buffers from this list must be mark as done/error/queued after streamoff of the
> respective queue in order to acknowledge that they are no longer in use by the
> HW. Not doing so will warn:
>
> videobuf2_common: driver bug: stop_streaming operation is leaving buf ...
>
> Though, there is no queue to easily iterate them. All driver endup having their
> own queue, or just leaving the buffers in the rdy_queue (which isn't better).
>
> Nicolas
>>> 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...
>>
>> 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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