linux-kernel - Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1

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Message-ID: <55E8DFCE.5040504@rock-chips.com>
Date:	Fri, 4 Sep 2015 08:03:26 +0800
From:	Shawn Lin <shawn.lin@...k-chips.com>
To:	Mark Brown <broonie@...nel.org>
Cc:	shawn.lin@...k-chips.com, Vinod Koul <vinod.koul@...el.com>,
	Heiko Stuebner <heiko@...ech.de>,
	Jaroslav Kysela <perex@...ex.cz>,
	Takashi Iwai <tiwai@...e.com>,
	Doug Anderson <dianders@...omium.org>,
	Olof Johansson <olofj@...gle.com>,
	Sonny Rao <sonnyrao@...omium.org>,
	Addy Ke <addy.ke@...k-chips.com>, dmaengine@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-rockchip@...ts.infradead.org, alsa-devel@...a-project.org,
	linux-spi@...r.kernel.org, Olof Johansson <olof@...om.net>
Subject: Re: [PATCH v3 8/9] spi: rockchip: modify DMA max burst to 1

On 2015/9/4 1:45, Mark Brown wrote:
> On Thu, Sep 03, 2015 at 09:41:43PM +0800, Shawn Lin wrote:
>> On 2015/9/3 20:54, Mark Brown wrote:
>
>>> If this is a quirk of the DMA controller why is it being fixed with a
>>> property specific to the SPI controller?  Can't the DMA controller just
>>> override the burst size?
>
>> Cool...that's a good question. Actually DMA controller can't do that since
>> block peripheral controller(e.g sd/emmc, they always access data by
>> block-512Bytes.) can't meet the case. So It's hard for dma controller know
>> who is the caller, and what should be done.
>
> You could take a guess based on request size, but that's going to be a
> bit error prone I imagine.
>

yes, not always cover all cases.

>> The only thing dma controller can do is avoid to execute DMAFLUSHP on its
>> own. But how about peripheral controller trigger non-multiple access? So
>> that's what I mentioned on covery letter that we should do "broken things"
>> for both dma controller and some peripherals.
>
> The other thing it could do is provide the information out via some
> internal Linux API which the drivers could query instead of directly
> having a DT property in each client driver.  That way at least the DT
> only needs the quirk in one place even if the clients need to handle it
> individually.

Good idea. Thanks, Mark.

>


-- 
Best Regards
Shawn Lin

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