From mboxrd@z Thu Jan  1 00:00:00 1970
From: b32955@freescale.com (Huang Shijie)
Date: Thu, 18 Oct 2012 14:45:41 +0800
Subject: [PATCH] dma: add new DMA control commands
In-Reply-To: <1350541111.5263.3.camel@vkoul-udesk3>
References: <1350538335-29026-1-git-send-email-b32955@freescale.com>
 <1350541111.5263.3.camel@vkoul-udesk3>
Message-ID: <507FA595.4020507@freescale.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

? 2012?10?18? 14:18, Vinod Koul ??:
> Why cant you do start (prepare clock etc) when you submit the descriptor
> to dmaengine. Can be done in tx_submit callback.
> Similarly remove the clock when dma transaction gets completed.
I ever thought this method too.

But it will become low efficient in the following case:

   Assuming the gpmi-nand driver has to read out 1024 pages in one 
_SINGLE_ read operation.
The gpmi-nand will submit the descriptor to dmaengine per page. So with 
your method,
the system will repeat the enable/disable dma clock 1024 time. At every 
enable/disable dma clock,
the system has to enable the clock chain and it's parents ...

But with this patch, we only need to enable/disable dma clock one time, 
just at we select the nand chip.

thanks
Huang Shijie