Re: DMA API issues

[Matt Porter <mporter@kernel.crashing.org>]

On Fri, Jun 18, 2004 at 07:19:58PM +0100, Ian Molton wrote:
> On Fri, 18 Jun 2004 11:07:21 -0700
> Matt Porter <mporter@kernel.crashing.org> wrote:
> 
> > Can't you just implement an arch-specific allocator for your 32KB
> > SRAM, then implement the DMA API streaming and dma_alloc/free APIs
> > on top of that?
> 
> Yes but thats not very generic is it? Im not the only one with this
> problem.

Yes, it's suboptimal, but an option.
 
> >  Since this architecture is obviously not designed
> > for performance
> 
> What makes you think writes to the 32K SRAM are any slower than to the
> SDRAM? the device is completely memory mapped.

I was referring to the small amount of space allowed for DMA
operations, obviously not the speed of accessing SRAM.
 
> >, it doesn't seem to be a big deal to have the streaming
> > APIs copy to/from the kmalloced (or whatever) buffer to/from the SRAM
> > allocated memory and then have those APIs return the proper dma_addr_t
> > for the embedded OHCI's address space view of the SRAM.
> 
> Again its a suboptimal solution, and on an architecture where the CPU
> isnt *that* fast in the first place it seems wrong to deliberately
> choose the slowest possible route...

Ok, so you're looking for a complete change to the streaming DMA APIs,
I guess.  Possibly requiring another call to allocate streaming-capable
memory since kmalloced buffers can't be used directly on your arch (or
all arches).  I agree it's suboptimal, it's one option to make it work
in the current API.

-Matt