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

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Date:   Wed, 1 Mar 2023 04:38:10 +0000
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Baoquan He <bhe@...hat.com>, linux-kernel@...r.kernel.org
Cc:     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,
        willy@...radead.org, 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 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...

> diff --git a/include/asm-generic/iomap.h b/include/asm-generic/iomap.h
> index 08237ae8b840..196087a8126e 100644
> --- a/include/asm-generic/iomap.h
> +++ b/include/asm-generic/iomap.h
> @@ -93,15 +93,15 @@ extern void __iomem *ioport_map(unsigned long port, unsigned int nr);
>  extern void ioport_unmap(void __iomem *);
>  #endif
>  
> -#ifndef ARCH_HAS_IOREMAP_WC
> +#ifndef ioremap_wc
>  #define ioremap_wc ioremap
>  #endif

... but it looks like this will break it, since in sfc/io.h
 `#ifdef ioremap_wc` will always be true (if I'm correctly
 understanding what we get via #include <linux/io.h>, which I'm
 probably not because asm includes always confuse me).
I.e. we're not just interested in "can code that calls ioremap_wc
 compile?", we care about whether we actually get WC, because
 we're making an optimisation decision based on it.