Messages in this thread | | | Date | Sat, 17 Aug 2019 14:07:29 -0700 (PDT) | From | Paul Walmsley <> | Subject | Re: [PATCH 15/26] asm-generic: ioremap_uc should behave the same with and without MMU |
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On Sat, 17 Aug 2019, Christoph Hellwig wrote:
> Whatever reason there is for the existence of ioremap_uc, and the fact > that it returns NULL by default on architectures with an MMU applies > equally to nommu architectures, so don't provide different defaults. > > In practice the difference is meaningless as the only portable driver > that uses ioremap_uc is atyfb which probably doesn't show up on nommu > devices. > > Signed-off-by: Christoph Hellwig <hch@lst.de>
[ ... ]
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h > index d02806513670..a98ed6325727 100644 > --- a/include/asm-generic/io.h > +++ b/include/asm-generic/io.h
[ ... ]
> @@ -1004,6 +985,21 @@ static inline void __iomem *ioremap_wt(phys_addr_t offset, size_t size) > } > #endif > > +/* > + * ioremap_uc is special in that we do require an explicit architecture > + * implementation. In general you do now want to use this function in a ^^^ not
> + * driver and use plain ioremap, which is uncached by default. Similarly ^ instead
> + * architectures should not implement it unless they have a very good > + * reason. > + */
Looks like this mess is only needed on x86 with certain graphics drivers and conflicts between MTRR and page table-based MMU attributes.
Reviewed-by: Paul Walmsley <paul.walmsley@sifive.com> Tested-by: Paul Walmsley <paul.walmsley@sifive.com> # rv32, rv64 boot
- Paul
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