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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 18 Oct 2012 11:18:53 -0400
From:	Huang Shijie <shijie8@...il.com>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	Huang Shijie <b32955@...escale.com>,
	Vinod Koul <vinod.koul@...ux.intel.com>, marex@...x.de,
	alsa-devel@...a-project.org, shawn.guo@...aro.org,
	linux@....linux.org.uk, tiwai@...e.de,
	artem.bityutskiy@...ux.intel.com,
	broonie@...nsource.wolfsonmicro.com, linux-mmc@...r.kernel.org,
	w.sang@...gutronix.de, perex@...ex.cz,
	linux-mtd@...ts.infradead.org, linux-i2c@...r.kernel.org,
	ben-linux@...ff.org, djbw@...com, khali@...ux-fr.org,
	cjb@...top.org, dwmw2@...radead.org, lrg@...com,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dma: add new DMA control commands

On Thu, Oct 18, 2012 at 5:29 AM, Jassi Brar <jaswinder.singh@...aro.org> wrote:
> On 18 October 2012 12:15, Huang Shijie <b32955@...escale.com> 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 ...
>>
>> But with this patch, we only need to enable/disable dma clock one time, just
>> at we select the nand chip.
>>
> If the clock is the dmac's property (not channels'), the toggling
> seems too aggressive.
> You could try using runtime_suspend/resume for clock
> disabling/enabling. How about employing autosuspend with a few ms
> delay?

Yes, employing the autosuspend is workable method too.o
But it's a little more complicated then this patch. You have to create
a thread or workqueue to
do the job.

What's more, I think other DMA engine may also meets the same issue as
the mxs-dma, such as the imx-sdma.
It's somehow a common issue to disable the clocks when no one use the
DMA engine.
Do you also suggest employing the autosuspend? Why not use a simple
way to handle this issue?
When the dma device want to use a DMA engine, it just needs to issue a
DMA_START command.

thanks
Huang Shijie
Huang Shijie
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/