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

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Date:	Thu, 18 Oct 2012 17:10:46 +0800
From:	Huang Shijie <b32955@...escale.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	Vinod Koul <vinod.koul@...ux.intel.com>, <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>,
	Huang Shijie <shijie8@...il.com>
Subject: Re: [PATCH] dma: add new DMA control commands

于 2012年10月18日 16:52, Russell King - ARM Linux 写道:
> On Thu, Oct 18, 2012 at 02:45:41PM +0800, Huang Shijie wrote:
>> 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 ...
> And what if you stop using clk_prepare_enable(), and prepare the clock
> when the channel is requested and only use clk_enable() in the tx_submit
yes. it's a little better.
There is nearly no difference between the clk_prepare_enable() and 
clk_enable() in actually.
the clk_gate2_ops does not have any @->prepare.

thanks
Huang Shijie

> method?
>


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