From mboxrd@z Thu Jan  1 00:00:00 1970
From: robert.jarzmik@free.fr (Robert Jarzmik)
Date: Sat, 24 Oct 2015 11:57:53 +0200
Subject: [PATCH v2 1/3] dmaengine: virt-dma: don't always free descriptor
 upon completion
References: <1444766070-26915-1-git-send-email-robert.jarzmik@free.fr>
Message-ID: <87oafowahl.fsf@belgarion.home>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

Robert Jarzmik <robert.jarzmik@free.fr> writes:

> This patch attempts to enhance the case of a transfer submitted multiple
> times, and where the cost of creating the descriptors chain is not
> negligible.
>
> This happens with big video buffers (several megabytes, ie. several
> thousands of linked descriptors in one scatter-gather list). In these
> cases, a video driver would want to do :
>  - tx = dmaengine_prep_slave_sg()
>  - dma_engine_submit(tx);
>  - dma_async_issue_pending()
>  - wait for video completion
>  - read video data (or not, skipping a frame is also possible)
>  - dma_engine_submit(tx)
>    => here, the descriptors chain recalculation will take time
>    => the dma coherent allocation over and over might create holes in
>       the dma pool, which is counter-productive.
>  - dma_async_issue_pending()
>  - etc ...
>
> In order to cope with this case, virt-dma is modified to prevent freeing
> the descriptors upon completion if DMA_CTRL_REUSE flag is set in the
> transfer.
>
> This patch is a respin of the former DMA_CTRL_ACK approach, which was
> reverted due to a regression in audio drivers.
>
> Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
> ---
> Since v1: added doxygen commit to vchan_tx_desc_free

Hi Vinod,

Is this serie good for you or do you have remaining comments to be addressed ?

Cheers.

--
Robert