[PATCH 01/15] iio: buffer-dma: Get rid of incoming/outgoing queues
Paul Cercueil
paul at crapouillou.net
Mon Nov 22 15:16:06 UTC 2021
Hi Lars,
Le lun., nov. 22 2021 at 16:08:51 +0100, Lars-Peter Clausen
<lars at metafoo.de> a écrit :
> On 11/21/21 9:08 PM, Paul Cercueil wrote:
>>
>>
>> Le dim., nov. 21 2021 at 19:49:03 +0100, Lars-Peter Clausen
>> <lars at metafoo.de> a écrit :
>>> 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 at metafoo.de> 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 at crapouillou.net>
>>>>> 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.
>>>
>>
>> That's still the case after the DMABUF changes of the series. Or can
>> you point me exactly what you think is broken?
>>
> When you allocate a DMABUF with the allocate IOCTL and then submit it
> with the enqueue IOCTL before the buffer is enabled it will end up
> marked as queued, but not actually be queued anywhere.
>
Ok, it works for me because I never enqueue blocks before enabling the
buffer. I can add a requirement that blocks must be enqueued only after
the buffer is enabled.
Cheers,
-Paul
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