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

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Message-ID: <20160318203352.GL2566@sirena.org.uk>
Date:	Fri, 18 Mar 2016 20:33:52 +0000
From:	Mark Brown <broonie@...nel.org>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Michal Suchanek <hramrach@...il.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 Fri, Mar 18, 2016 at 09:23:10PM +0100, Maxime Ripard wrote:
> On Thu, Mar 17, 2016 at 12:54:08PM +0100, Michal Suchanek wrote:

> > Very few device drivers would work with 63byte transfers only and the
> > code for manually driving the CS line in case the DMA engine fails to
> > configure will necessarily go untested most of the time since most
> > systems will have DMA configured properly.

> That's not true. A significant portion would work. I don't like to
> make up numbers, but I guess only the EEPROMs and rather big screens
> wouldn't work.

You'll probably also see devices doing things like firmware downloads,
there's a bunch of applications for larger transfers.  Like you say it's
definitely not going to be a universal problem though, there's many
devices that just use SPI for fast register access.

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