Date: Wed, 1 Oct 2014 10:27:05 +0200
From: Maxime Ripard <maxime.ripard@free-electrons.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: Vinod Koul <vinod.koul@intel.com>, dmaengine@vger.kernel.org,
        lars@metafoo.de, linux-kernel@vger.kernel.org,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        linux-arm-kernel@lists.infradead.org,
        Antoine =?iso-8859-1?Q?T=E9nart?= <antoine@free-electrons.com>
Subject: Re: [PATCH 7/9] dmaengine: Move slave caps to dma_device
Message-ID: <20141001082705.GF6884@lukather>
References: <1411808085-27792-1-git-send-email-maxime.ripard@free-electrons.com>
 <1411808085-27792-8-git-send-email-maxime.ripard@free-electrons.com>
 <20140927092846.GA5182@n2100.arm.linux.org.uk>
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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.
> >=20
> > However, this proved to be a bit overkill, since every driver filling t=
hese so
> > far were hardcoding it, disregarding which channel was actually given.
> >=20
> > Add these capabilities to the dma_device structure, so that drivers can=
 just
> > provide them at probe time, and be done with it.
>=20
> 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.
>=20
> 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

--=20
Maxime Ripard, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com

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