Unconditional registering EMDA platform devices

[Uwe Kleine-König]

Hello Arnd,

On Fri, Oct 24, 2014 at 06:14:01PM +0200, Arnd Bergmann wrote:
> On Friday 24 October 2014 16:29:04 Andrew Lunn wrote:
> > Hi Matt
> > 
> > I've had a report of a Debian kernel running on a Marvell XP system
Not really relevant, but it's a Armada 370, not XP system.

> > giving warnings:
> > 
> > [    0.114771] edma-dma-engine edma-dma-engine.0: Can't allocate PaRAM dummy slot
> > [    0.114794] edma-dma-engine: probe of edma-dma-engine.0 failed with error -5
> >
> > These seem to be coming from drivers/dma/emda.c
> > 
> > That driver has a subsys_initcall(edma_init);
> > 
> > and the edma_init function is unconditionally registering a driver and
> > a platform device. For a multiarch kernel, this is not a good idea.
> > 
> > Please could you make this conditionally. Maybe look into the DT and
> > see if the DMA is needed on the platform?
>  
> I just looked at that code an I'm completely confused about how that
> even works today. I do see that the driver is used on ATAGS based
> davinci machines, which means we can't just look into the DT.
> 
> The main problem seems to stem from arch/arm/common/edma.c being
> half the driver that provides interfaces to both drivers/dma/edma.c
> and to sound/soc/davinci/davinci-pcm.c, while drivers/dma/edma.c
> is not really a driver by itself. My preferred solution to this would
> be to move arch/arm/common/edma.c into drivers/dma/edma.c and still
> have it export its private API, but I assume that the dmaengine
> maintainers have already NAKed that approach.
Isn't the preferred solution that sound/soc/davinci/davinci-pcm.c only
uses dmaengine stuff and the private API goes away?

> Would the approach below work?
I didn't test it yet, but I assume it makes the warning disappear on
machines without an "edma" platform device. So it would solve my
problem.

> 8<-------
> Subject: dma: edma: move device registration to platform code
> 
> The horrible split between the low-level part of the edma support
> and the dmaengine front-end driver causes problems on multiplatform
> kernels. This is an attempt to improve the situation slightly
> by only registering the dmaengine devices that are actually
> present.
> 
> Signed-off-by: Arnd Bergmann <arnd at arndb.de>
> [...]
> diff --git a/drivers/dma/edma.c b/drivers/dma/edma.c
> index 123f578d6dd3..4cfaaa5a49be 100644
> --- a/drivers/dma/edma.c
> +++ b/drivers/dma/edma.c
There is a comment in drivers/dma/edma.c reading:

/*
 * This will go away when the private EDMA API is folded
 * into this driver and the platform device(s) are
 * instantiated in the arch code. We can only get away
 * with this simplification because DA8XX may not be built
 * in the same kernel image with other DaVinci parts. This
 * avoids having to sprinkle dmaengine driver platform devices
 * and data throughout all the existing board files.
 */

Just looking into arch/arm/mach-davinci/Kconfig it seems wrong that
DA8XX may not be enabled with other DaVinci parts. So probably there is
really more broken here ...

Best regards
Uwe