linux-kernel - Re: [PATCH 1/2] spi: sun4i: add DMA support

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Date:	Thu, 17 Mar 2016 11:43:08 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	Priit Laes <plaes@...es.org>, Chen-Yu Tsai <wens@...e.org>,
	linux-spi <linux-spi@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Emilio López <emilio@...pez.com.ar>
Subject: Re: [PATCH 1/2] spi: sun4i: add DMA support

On Thu, Mar 17, 2016 at 11:58:05AM +0100, Michal Suchanek wrote:
> On 17 March 2016 at 08:27, Maxime Ripard

> > You're mixing two things up: the fact that we can't do more than the
> > FIFO length in PIO and that we're missing DMA support. We have patches
> > to address both, and there's no depedency between the two.

> The only thing is that although DMA is optional on pretty much any
> system you will have DMA available unless you broke your config. You
> really do want the DMA support when it is available. So there will be
> nobody testing the non-DMA part and it will be prone to bitrot.

Well, it might be worth doing PIO for very short transfers even if you
have DMA - it's quite common for this to perform better.

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