linux-kernel - Re: [PATCH 15/30] usb/musb: use a Kconfig choice to pick the right DMA method

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Message-ID: <1757336.Qk72n3s00p@wuerfel>
Date:	Sun, 02 Oct 2011 20:00:31 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	Tony Lindgren <tony@...mide.com>, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org, Felipe Balbi <balbi@...com>
Subject: Re: [PATCH 15/30] usb/musb: use a Kconfig choice to pick the right DMA method

On Sunday 02 October 2011 17:14:47 Russell King - ARM Linux wrote:
> On Sun, Oct 02, 2011 at 04:45:45PM +0200, Arnd Bergmann wrote:
> > The logic to allow only one DMA driver in MUSB is currently
> > flawed, because it also allows picking no DMA driver at all
> > and also not selecting PIO mode.
> > 
> > Using a choice statement makes this foolproof for now and
> > also simplifies the Makefile.
> > 
> > Unfortunately, we will have to revisit this when we start
> > supporting multiple ARM platforms in a single kernel binary,
> > because at that point we will actually need to select
> > multiple DMA drivers and pick the right one at run-time.
> 
> I thought there was some work going on to convert this to use the
> dmaengine stuff?

That would certainly be the best solution here, I wasn't aware
that it has already been discussed.

Unfortunately, even with the dma parts out of the way there is
a lot that needs to be done to make musb, ehci or ohci
really cross-platform. Right now, you can only have one
platform driver glue for each of those drivers, and they
should eventually be converted to a large library module for
the core, with independent platform driver front-end, similar
to the recent conversion of the sdhci driver by Shawn Guo,
and the way that a lot of the other common drivers work.

	Arnd
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