Pawel Osciak wrote:
> Architectures with non-coherent CPU cache (e.g. ARM) may require a cache
> flush or invalidation before starting a hardware operation if the data in
> a video buffer being queued has been touched by the CPU.
>
> This patch adds calls to sync before a hardware operation that are expected
> to be interpreted and handled by each memory type-specific module.
>
> Whether it is a sync before or after the operation can be determined from
> the current buffer state: VIDEOBUF_DONE and VIDEOBUF_ERROR indicate a sync
> called after an operation.
Hi Pawel,
After analyzing this patch, maybe the better is to add a check for dma
coherency. So, instead of directly calling sync,the better is to check
if !dma_is_consistent(), to avoid adding a penalty on architectures
where the cache is coherent.
>
> diff --git a/drivers/media/video/videobuf-core.c b/drivers/media/video/videobuf-core.c
> index bb0a1c8..e56c67a 100644
> --- a/drivers/media/video/videobuf-core.c
> +++ b/drivers/media/video/videobuf-core.c
> @@ -561,6 +561,8 @@ int videobuf_qbuf(struct videobuf_queue *q,
> goto done;
> }
>
> + CALL(q, sync, q, buf);
> +
> list_add_tail(&buf->stream, &q->stream);
> if (q->streaming) {
> spin_lock_irqsave(q->irqlock, flags);
> @@ -761,6 +763,8 @@ static ssize_t videobuf_read_zerocopy(struct videobuf_queue *q,
> if (0 != retval)
> goto done;
>
> + CALL(q, sync, q, q->read_buf);
> +
> /* start capture & wait */
> spin_lock_irqsave(q->irqlock, flags);
> q->ops->buf_queue(q, q->read_buf);
> @@ -826,6 +830,8 @@ ssize_t videobuf_read_one(struct videobuf_queue *q,
> goto done;
> }
>
> + CALL(q, sync, q, q->read_buf);
> +
> spin_lock_irqsave(q->irqlock, flags);
> q->ops->buf_queue(q, q->read_buf);
> spin_unlock_irqrestore(q->irqlock, flags);
> @@ -893,6 +899,9 @@ static int __videobuf_read_start(struct videobuf_queue *q)
> err = q->ops->buf_prepare(q, q->bufs[i], field);
> if (err)
> return err;
> +
> + CALL(q, sync, q, q->read_buf);
> +
> list_add_tail(&q->bufs[i]->stream, &q->stream);
> }
> spin_lock_irqsave(q->irqlock, flags);
> diff --git a/drivers/media/video/videobuf-dma-sg.c b/drivers/media/video/videobuf-dma-sg.c
> index fa78555..2b153f8 100644
> --- a/drivers/media/video/videobuf-dma-sg.c
> +++ b/drivers/media/video/videobuf-dma-sg.c
> @@ -50,6 +50,9 @@ MODULE_LICENSE("GPL");
> #define dprintk(level, fmt, arg...) if (debug >= level) \
> printk(KERN_DEBUG "vbuf-sg: " fmt , ## arg)
>
> +#define is_sync_after(vb) \
> + (vb->state == VIDEOBUF_DONE || vb->state == VIDEOBUF_ERROR)
> +
> /* --------------------------------------------------------------------- */
>
> struct scatterlist*
> @@ -516,6 +519,9 @@ static int __videobuf_sync(struct videobuf_queue *q,
> BUG_ON(!mem);
> MAGIC_CHECK(mem->magic,MAGIC_SG_MEM);
>
> + if (!is_sync_after(buf))
> + return 0;
> +
> return videobuf_dma_sync(q,&mem->dma);
> }
>
--
Cheers,
Mauro
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