Re: AMD64 dma_alloc_coherent crashes on non PCI device (was SATA open bugs)

[James Bottomley <James.Bottomley@SteelEye.com>]

On Fri, 2007-08-10 at 00:17 +0100, Alan Cox wrote:
> > If the device you're passing has a NULL dma_mask pointer that means the
> > platform hasn't set it up correctly for dma ... and that's the
> 
> Well it may not do DMA. 

Unfortunately, I don't think we've considered that possibility in the
integration of the dma API and generic devices.

> > underlying problem (although it's not necessarily a libata problem): you
> > can't call dma_ operations on a device that hasn't been set up in the
> > platform for it.
> 
> Right.
> 
> Ok so what is the right way given a random *correctly* set up device that
> may or may not be DMA capable to determine this. Its an arbitary device
> pointer for an arbitary device class on an arbitary platform which may or
> may not support DMA for this device class ?
> 
> Can I called dma_alloc_coherent and get a NULL back or do we need a
> device_can_dma() check in each platform ?

Fundamentally it's a different question.  The dma_alloc is just saying
can you set up a coherent memory area that this device can reach.  Often
the platform cannot necessarily discover this.  I'd say the best signal
is that the driver has called dma_set_mask(dev, DMA_MASK_NONE) (which
isn't defined yet). So the platform has a signal that the device isn't
DMA capable.

James