Messages in this thread | | | Date | Mon, 3 Nov 2008 09:37:27 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] Add io-mapping functions to dynamically map large device apertures |
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* Keith Packard <keithp@keithp.com> wrote:
> On Fri, 2008-10-31 at 10:21 +0100, Ingo Molnar wrote: > > > it's ugly and inflexible to put x86 dependencies into generic headers. > > (even though with a high likelyhood 32-bit x86 will be the only arch > > to ever implement the iomap_atomic() APIs) > > > > Instead please add a HAVE_ATOMIC_IOMAP define to arch/x86/Kconfig: > > > > config HAVE_ATOMIC_IOMAP > > def_bool y > > depends on X86_32 > > > > ... and use #ifndef HAVE_ATOMIC_IOMAP in include/linux/io-mapping.h > > instead of #ifdef CONFIG_X86_64. > > Just to clarify the issue here: there are two separate > implementations of the io_mapping API -- one for 'large address > space' machines where ioremap_wc can handle the typical graphics > aperture within the kernel virtual map, and the other using > iomap_atomic_prot_pfn for machines with puny address spaces. > > All large address space machines can provide the io_mapping API > without any archtecture-specific support. For efficient 32-bit > io_mapping support, we require the new iomap_atomic_prot_pfn > function. > > So, it seems like what I want to do is use the large address space > code on any machine which supports it, and then use the > iomap_atomic_prot_pfn version for small address space machines which > have the iomap_atomic_prot_pfn function.
Correct.
> What I think you're suggesting is to just assume that machines > without iomap_atomic_prot_pfn have address spaces large enough to > support the ioremap_wc path. The alternative is to create a third > (slow) path (which I did before the iomap_atomic_prot_pfn API was > introduced) that uses ioremap_wc at run time for small address space > machines without iomap_atomic_prot_pfn. > > Let me know which you'd prefer and I'll get a patch out ASAP.
Please lets keep it simple: i.e. always use ioremap_wc() when there's no iomap_atomic_prot_pfn() 32-bit API provided.
( and by all means ioremap_wc() will just work fine on most 32-bit architectures out of box: they dont go about trying to map hundreds of megabytes of graphics aperture. If they nevertheless need it, they can implement iomap_atomic_prot_pfn() to add support. )
Ingo
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