linux-kernel - Re: [PATCH] dma: add new DMA control commands

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Date:	Thu, 18 Oct 2012 14:45:41 +0800
From:	Huang Shijie <b32955@...escale.com>
To:	Vinod Koul <vinod.koul@...ux.intel.com>
CC:	<djbw@...com>, <khali@...ux-fr.org>, <ben-linux@...ff.org>,
	<w.sang@...gutronix.de>, <cjb@...top.org>, <dwmw2@...radead.org>,
	<lrg@...com>, <broonie@...nsource.wolfsonmicro.com>,
	<perex@...ex.cz>, <tiwai@...e.de>, <shawn.guo@...aro.org>,
	<marex@...x.de>, <artem.bityutskiy@...ux.intel.com>,
	<linux-kernel@...r.kernel.org>, <linux-i2c@...r.kernel.org>,
	<linux-mmc@...r.kernel.org>, <linux-mtd@...ts.infradead.org>,
	<alsa-devel@...a-project.org>,
	<linux-arm-kernel@...ts.infradead.org>, <linux@....linux.org.uk>,
	Huang Shijie <shijie8@...il.com>
Subject: Re: [PATCH] dma: add new DMA control commands

于 2012年10月18日 14:18, Vinod Koul 写道:
> 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




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