Re: [PATCH v5 01/17] asm-generic/iomap.h: remove ARCH_HAS_IOREMAP_xx macros

[Matthew Wilcox]

On Wed, Mar 01, 2023 at 04:38:10AM +0000, Edward Cree wrote:
> On 01/03/2023 03:42, Baoquan He wrote:
> > diff --git a/drivers/net/ethernet/sfc/io.h b/drivers/net/ethernet/sfc/io.h
> > index 30439cc83a89..07f99ad14bf3 100644
> > --- a/drivers/net/ethernet/sfc/io.h
> > +++ b/drivers/net/ethernet/sfc/io.h
> > @@ -70,7 +70,7 @@
> >   */
> >  #ifdef CONFIG_X86_64
> >  /* PIO is a win only if write-combining is possible */
> > -#ifdef ARCH_HAS_IOREMAP_WC
> > +#ifdef ioremap_wc
> >  #define EFX_USE_PIO 1
> >  #endif
> >  #endif
> 
> So I don't know how valid what we're doing here is...

Well, x86 defines ARCH_HAS_IOREMAP_WC unconditionally, so it doesn't
affect you ... but you raise a good question about how a driver can
determine if it's actually getting WC memory.