Re: [PATCH 1/2] dma-mapping: fix page attributes for dma_mmap_*

[Shawn Anastasio]

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.

> > 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.

> > 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`?