Re: [PATCH 2/2] media: v4l2-mem2mem: add a list for buf used by hw

[Hsia-Jun Li <Randy.Li@synaptics.com>]

On 7/17/23 22:07, Nicolas Dufresne wrote:
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>
> 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@synaptics.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@synaptics.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