Re: DMA API issues

[Jamey Hicks]

Matt Porter wrote:

> On Fri, Jun 18, 2004 at 02:33:18PM -0400, Jamey Hicks wrote:
>  
>
> Yes, it can be cleaner, but it's not something I would say is
> completely broken with the DMA API.  It does provide a way to
> make your device specific implementation, regardless of whether
> it's managed ideally via a struct device pointer.  Migrating to
> dev->dma* sounds suspiciously like a 2.7ism.
>  
The DMA API is certainly not completely broken.  Except for page_to_dma 
needing struct device the interface could be implemented with per-device 
dma operation implementations.

> > described, but there is already a good start towards that support in 
> > 2.6.  The other thing that might be needed is passing device to 
> >    
>
> Where's that code?
>
>  
arch/arm/common/dmabounce.c

> > page_to_dma so that device specific dma addresses can be constructed.
> >    
>
> A struct device argument to page_to_dma seems like a no brainer to be
> included.
>
>  
>
> > Deepak Saxena wrote a pretty good summary as part if the discussion 
> > about this issue on the linux-arm-kernel mailing list:
> >
> > http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2004-June/022796.html
> >    
>
> Ahh, ok.  Deepak and I have discussed this idea F2F on a several
> occassions, I recall he needed it for the small floating PCI window
> he has to manage on the IXP* ports.  It may help in some embedded
> PPC areas as well.
>
>  
>
> > I think I'm looking for something like the PARISC hppa_dma_ops but more 
> > generic:
> >  
> > http://lists.arm.linux.org.uk/pipermail/linux-arm-kernel/2004-June/022813.html
> >    
>
> I see that's somewhat like what David Brownell suggested before...a single
> pointer to a set of dma ops from struct device.  hppa_dma_ops translated
> into a generic dma_ops entity with fields corresponding to existing
> DMA API calls would be a good starting point. We can get rid of some
> address translation hacks in a lot of custom embedded PPC drivers
> with something like this.
>  
Yes, I think this would be generally useful.

Jamey


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