Re: DMA API issues

[Jamey Hicks <jamey.hicks@hp.com>]

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