From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Fri, 14 Sep 2012 09:30:50 +0100
Subject: [PATCH] mxs/dma: Enlarge the CCW descriptor area to 4 pages
In-Reply-To: <1347591975.1943.12.camel@vkoul-udesk3>
References: <1346731465-6301-1-git-send-email-marex@denx.de>
 <20120905014000.GP2362@S2101-09.ap.freescale.net>
 <201209050346.39253.marex@denx.de> <1347591975.1943.12.camel@vkoul-udesk3>
Message-ID: <20120914083050.GA12245@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Fri, Sep 14, 2012 at 08:36:15AM +0530, Vinod Koul wrote:
> On Wed, 2012-09-05 at 03:46 +0200, Marek Vasut wrote:
> > One way to fix this is to recycle descriptors that were already used during the 
> > transfer, but can we really do it fast enough, so the DMA would do it's job at 
> > one end of the descriptor chain and we'd be building the other?
> See the comment in dma_ctrl_flags:
> * @DMA_CTRL_ACK - if clear, the descriptor cannot be reused until the client
> *  acknowledges receipt, i.e. has has a chance to establish any dependency
> *  chains
> Setting this would mean that driver can reuse the descriptor once the
> transaction has completed.

Actually, that has little meaning for slave DMA descriptors (other than
it should already be set for consistency with the async_tx stuff, which
has the above mentioned depenedency chains.)

Once completed, descriptors can be reused irrespective of the above flag.