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Date:   Wed, 06 Nov 2019 09:56:34 -0800 (PST)
Subject:     Re: [PATCH 10/21] asm-generic: ioremap_uc should behave the same with and without MMU
In-Reply-To: <20191029064834.23438-11-hch@lst.de>
CC:     Arnd Bergmann <arnd@arndb.de>, guoren@kernel.org, monstr@monstr.eu,
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From:   Palmer Dabbelt <palmer@dabbelt.com>
To:     Christoph Hellwig <hch@lst.de>
Message-ID: <mhng-3f709a8a-a8c3-4612-b4de-847d13b4af0a@palmer-si-x1c4>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@lst.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@dabbelt.com>