On 8/7/19 8:04 AM, Christoph Hellwig wrote:

Actually it is typical modern Linux style to just provide a prototype
and then use "if (IS_ENABLED(CONFIG_FOO))" to guard the call(s) to it.

I see.

quoted

Also, like Will mentioned earlier, the function name isn't entirely
accurate anymore. I second the suggestion of using something like
arch_dma_noncoherent_pgprot().

As mentioned I plan to remove arch_dma_mmap_pgprot for 5.4, so I'd
rather avoid churn for the short period of time.

Yeah, fair enough.

quoted

As for your idea of defining
pgprot_dmacoherent for all architectures as

#ifndef pgprot_dmacoherent
#define pgprot_dmacoherent pgprot_noncached
#endif

I think that the name here is kind of misleading too, since this
definition will only be used when there is no support for proper
DMA coherency.

Do you have a suggestion for a better name?  I'm pretty bad at naming,
so just reusing the arm name seemed like a good way to avoid having
to make naming decisions myself.

Good question. Perhaps something like `pgprot_dmacoherent_fallback`
would better convey that this is only used for devices that don't
support DMA coherency? Or maybe `pgprot_dma_noncoherent`?


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