linux-kernel - Re: [PATCH 10/21] asm-generic: ioremap_uc should behave the same with and without MMU

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Message-ID: <mhng-3f709a8a-a8c3-4612-b4de-847d13b4af0a@palmer-si-x1c4>
Date:   Wed, 06 Nov 2019 09:56:34 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     Christoph Hellwig <hch@....de>
CC:     Arnd Bergmann <arnd@...db.de>, guoren@...nel.org, monstr@...str.eu,
        green.hu@...il.com, deanbo422@...il.com, gxt@....edu.cn,
        x86@...nel.org, linux-alpha@...r.kernel.org,
        linux-snps-arc@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-hexagon@...r.kernel.org, linux-ia64@...r.kernel.org,
        linux-m68k@...ts.linux-m68k.org, linux-mips@...r.kernel.org,
        nios2-dev@...ts.rocketboards.org, openrisc@...ts.librecores.org,
        linux-parisc@...r.kernel.org, linux-riscv@...ts.infradead.org,
        linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
        sparclinux@...r.kernel.org, linux-xtensa@...ux-xtensa.org,
        linux-mtd@...ts.infradead.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject:     Re: [PATCH 10/21] asm-generic: ioremap_uc should behave the same with and without MMU

On Mon, 28 Oct 2019 23:48:23 PDT (-0700), Christoph Hellwig wrote:
> Whatever reason there is for the existence of ioremap_uc, and the fact
> that it returns NULL by default on architectures with an MMU applies
> equally to nommu architectures, so don't provide different defaults.
>
> In practice the difference is meaningless as the only portable driver
> that uses ioremap_uc is atyfb which probably doesn't show up on nommu
> devices.
>
> Signed-off-by: Christoph Hellwig <hch@....de>
> ---
>  include/asm-generic/io.h | 36 ++++++++++++++++--------------------
>  1 file changed, 16 insertions(+), 20 deletions(-)
>
> diff --git a/include/asm-generic/io.h b/include/asm-generic/io.h
> index d02806513670..a98ed6325727 100644
> --- a/include/asm-generic/io.h
> +++ b/include/asm-generic/io.h
> @@ -935,18 +935,7 @@ static inline void *phys_to_virt(unsigned long address)
>   * defined your own ioremap_*() variant you must then declare your own
>   * ioremap_*() variant as defined to itself to avoid the default NULL return.
>   */
> -
> -#ifdef CONFIG_MMU
> -
> -#ifndef ioremap_uc
> -#define ioremap_uc ioremap_uc
> -static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
> -{
> -	return NULL;
> -}
> -#endif
> -
> -#else /* !CONFIG_MMU */
> +#ifndef CONFIG_MMU
>
>  /*
>   * Change "struct page" to physical address.
> @@ -980,14 +969,6 @@ static inline void __iomem *ioremap_nocache(phys_addr_t offset, size_t size)
>  }
>  #endif
>
> -#ifndef ioremap_uc
> -#define ioremap_uc ioremap_uc
> -static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
> -{
> -	return ioremap_nocache(offset, size);
> -}
> -#endif
> -
>  #ifndef ioremap_wc
>  #define ioremap_wc ioremap_wc
>  static inline void __iomem *ioremap_wc(phys_addr_t offset, size_t size)
> @@ -1004,6 +985,21 @@ static inline void __iomem *ioremap_wt(phys_addr_t offset, size_t size)
>  }
>  #endif
>
> +/*
> + * ioremap_uc is special in that we do require an explicit architecture
> + * implementation.  In general you do now want to use this function in a

Presumably that's supposed to be "do not want to use"?

> + * driver and use plain ioremap, which is uncached by default.  Similarly
> + * architectures should not implement it unless they have a very good
> + * reason.
> + */
> +#ifndef ioremap_uc
> +#define ioremap_uc ioremap_uc
> +static inline void __iomem *ioremap_uc(phys_addr_t offset, size_t size)
> +{
> +	return NULL;
> +}
> +#endif
> +
>  #ifdef CONFIG_HAS_IOPORT_MAP
>  #ifndef CONFIG_GENERIC_IOMAP
>  #ifndef ioport_map

With the fix:

Reviewed-by: Palmer Dabbelt <palmer@...belt.com>