linux-kernel - Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

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Date:	Tue, 31 May 2016 14:27:07 +0100
From:	Mark Brown <broonie@...nel.org>
To:	Michal Suchanek <hramrach@...il.com>
Cc:	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-sunxi <linux-sunxi@...glegroups.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>,
	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@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 5/5] RFC spi: sun4i: add DMA support

On Tue, May 31, 2016 at 12:44:54PM +0200, Michal Suchanek wrote:
> On 30 May 2016 at 17:50, Mark Brown <broonie@...nel.org> wrote:
> > On Mon, May 30, 2016 at 05:28:10PM +0200, Michal Suchanek wrote:

> >> It's what the driver did to start with and it was requested to fall
> >> back to non-DMA in the case DMA is not available.

> > Why?  I really can't see any sensible use case for this that doesn't
> > have a better solution available.

> Of course, the solution is to compile in the DMA driver.

> It's been argued that some drivers which use only short transfers will
> just work.

With nothing else in the system that needs DMA?  It's making the
performance of the system less reliable for the benefit of a very narrow
use case.

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