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@xxxxxx>
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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
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@@ -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@xxxxxxxxxx> Tested-by: Paul Walmsley <paul.walmsley@xxxxxxxxxx> # rv32, rv64 boot - Paul
