linux-kernel - Re: [PATCH 7/9] dmaengine: Move slave caps to dma

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Date:	Wed, 1 Oct 2014 10:27:05 +0200
From:	Maxime Ripard <maxime.ripard@...e-electrons.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Vinod Koul <vinod.koul@...el.com>, dmaengine@...r.kernel.org,
	lars@...afoo.de, linux-kernel@...r.kernel.org,
	Laurent Pinchart <laurent.pinchart@...asonboard.com>,
	linux-arm-kernel@...ts.infradead.org,
	Antoine Ténart <antoine@...e-electrons.com>
Subject: Re: [PATCH 7/9] dmaengine: Move slave caps to dma_device

On Sat, Sep 27, 2014 at 10:28:47AM +0100, Russell King - ARM Linux wrote:
> On Sat, Sep 27, 2014 at 10:54:43AM +0200, Maxime Ripard wrote:
> > The previous code was relying on the fact that the slave_caps were to be
> > defined on a per channel basis.
> > 
> > However, this proved to be a bit overkill, since every driver filling these so
> > far were hardcoding it, disregarding which channel was actually given.
> > 
> > Add these capabilities to the dma_device structure, so that drivers can just
> > provide them at probe time, and be done with it.
> 
> This is also buggy for the same reason as patch 6.

Indeed

> The only way to do this is to either have a flag day, fixing all drivers
> at once (which isn't going to happen) or leave the caps code as-is, and
> provide a library function which drivers can hook into the caps callback
> which retrieves the information from dma_device.
> 
> That way, DMA engine drivers which are using the new method can just
> install the new function, and those which haven't been updated with
> capabilities can carry on as they are, and are detectable to drivers.

Which is pretty much the current behaviour, isn't it?

> What would be acceptable is to have the DMA engine registration function
> spot the lack of DMA caps function and print a warning at boot to
> encourage people to add it.

That would be an option too.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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