Re: [PATCH 01/15] iio: buffer-dma: Get rid of incoming/outgoing queues

[Lars-Peter Clausen]

On 11/21/21 6:52 PM, Paul Cercueil wrote:
> Hi Lars,
>
> Le dim., nov. 21 2021 at 17:23:35 +0100, Lars-Peter Clausen 
> <lars@xxxxxxxxxx> a écrit :
> > On 11/15/21 3:19 PM, Paul Cercueil wrote:
> > > The buffer-dma code was using two queues, incoming and outgoing, to
> > > manage the state of the blocks in use.
> > >
> > > While this totally works, it adds some complexity to the code,
> > > especially since the code only manages 2 blocks. It is much easier to
> > > just check each block's state manually, and keep a counter for the next
> > > block to dequeue.
> > >
> > > Since the new DMABUF based API wouldn't use these incoming and outgoing
> > > queues anyway, getting rid of them now makes the upcoming changes
> > > simpler.
> > >
> > > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > The outgoing queue is going to be replaced by fences, but I think we 
> > need to keep the incoming queue.
>
> Blocks are always accessed in sequential order, so we now have a 
> "queue->next_dequeue" that cycles between the buffers allocated for 
> fileio.
>
> > > [...]
> > > @@ -442,28 +435,33 @@ EXPORT_SYMBOL_GPL(iio_dma_buffer_disable);
> > >   static void iio_dma_buffer_enqueue(struct iio_dma_buffer_queue 
> > > *queue,
> > >       struct iio_dma_buffer_block *block)
> > >   {
> > > -    if (block->state == IIO_BLOCK_STATE_DEAD) {
> > > +    if (block->state == IIO_BLOCK_STATE_DEAD)
> > >           iio_buffer_block_put(block);
> > > -    } else if (queue->active) {
> > > +    else if (queue->active)
> > >           iio_dma_buffer_submit_block(queue, block);
> > > -    } else {
> > > +    else
> > >           block->state = IIO_BLOCK_STATE_QUEUED;
> > > -        list_add_tail(&block->head, &queue->incoming);
> > If iio_dma_buffer_enqueue() is called with a dmabuf and the buffer is 
> > not active, it will be marked as queued, but we don't actually keep a 
> > reference to it anywhere. It will never be submitted to the DMA, and 
> > it will never be signaled as completed.
>
> We do keep a reference to the buffers, in the queue->fileio.blocks 
> array. When the buffer is enabled, all the blocks in that array that 
> are in the "queued" state will be submitted to the DMA.
But not when used in combination with the DMA buf changes later in this 
series.