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SubjectRe: [PATCH] libata-sff: Don't call bmdma_stop on non DMA capable controllers
Linus Torvalds wrote:
>
> On Fri, 26 Jan 2007, David Woodhouse wrote:
>> You're thinking of MMIO, while the case we were discussing was PIO. My
>> laptop is perfectly happy to assign PIO resources from zero.
>
> I was indeed thinking MMIO, but I really think it should extend to PIO
> also. It certainly is (again) true on PC's, where the low IO space is
> special and reserved for motherboard/system devices.

Via the even-less-of-an-excuse-than-you-thought department:

Many (most?) non-x86 handle PIO via special mappings and additional
serialization instructions, but otherwise treat PIO register space in a
very similar manner to MMIO.

Thus, it's /easier/ on non-x86 to ensure that PIO addresses never land
at zero, because you must remap /anyway/. It's only on x86 that PIO
register spaces are accessed by vastly different CPU instructions. Most
other arches convert PIO accesses into massage+mmio R/W+massage.

On sparc64, for example, after I pointed this out to DaveM, he was able
to implement the new iomap interface without the 'if (pio-mem-area)'
branch present on x86.

Jeff



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