linux-kernel - Re: [PATCH v5 01/17] asm-generic/iomap.h: remove ARCH_HAS_IOREMAP

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Message-ID: <Y/7eceqZ+89iPm1C@casper.infradead.org>
Date:   Wed, 1 Mar 2023 05:11:13 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     Edward Cree <ecree.xilinx@...il.com>
Cc:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, linux-mm@...ck.org, arnd@...db.de,
        christophe.leroy@...roup.eu, hch@...radead.org,
        agordeev@...ux.ibm.com, wangkefeng.wang@...wei.com,
        schnelle@...ux.ibm.com, David.Laight@...lab.com, shorne@...il.com,
        loongarch@...ts.linux.dev, linux-m68k@...ts.linux-m68k.org,
        linux-mips@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        x86@...nel.org, netdev@...r.kernel.org,
        Martin Habets <habetsm.xilinx@...il.com>
Subject: Re: [PATCH v5 01/17] asm-generic/iomap.h: remove ARCH_HAS_IOREMAP_xx
 macros

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.