Re: io resources and cached mappings (was: [git pull] drm patches for 2.6.27-rc1)

[Keith Packard <keithp@keithp.com>]

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On Sun, 2008-10-19 at 19:53 +0200, Ingo Molnar wrote:

> Note how simple and consistent it all gets: IO resources already know 
> their physical location and their size limits. Being able to cache an 
> ioremap in a mapping [and being able to use atomic kmaps on 32-bit] is a 
> relatively simple and natural extension to the concept.

I'm not sure I see any value in caching mappings here; we're mostly
interested in copying lots of data onto the card and so we use a lot of
different mappings; atomic mappings are easy to use, and efficient
enough.

Also, if we're using a resource, I'd like to just use byte offsets and
not pfns; the resource presumably knows the base address.

> i think we need to finalize the API names and their abstraction level, 
> and then could even merge those APIs into v2.6.28 on a fast path, to 
> enable you to use it. It does not interact with anything else so it 
> should be safe to do.

Let's figure out the API we want, then figure out whether it makes sense
to stick it into 2.6.28 or whether we just want to wait for .29. I don't
mind rewriting the driver for the next release.

I will probably use something like the io_reserve stuff for .28 though;
it makes the code easier to read and gives us good performance on 64 bit
kernels.

-- 
keith.packard@intel.com

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