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Date: Fri, 4 Aug 2017 09:32:40 +0200
From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: David Woodhouse <dwmw2@infradead.org>,
        Brian Norris <computersforpeace@gmail.com>,
        Marek Vasut <marek.vasut@gmail.com>,
        Richard Weinberger <richard@nod.at>,
        Cyrille Pitchen <cyrille.pitchen@wedev4u.fr>,
        Jingoo Han <jg1.han@samsung.com>, Simon Baatz <gmbnomis@gmail.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        Arvind Yadav <arvind.yadav.cs@gmail.com>,
        linux-mtd@lists.infradead.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] mtd: orion-nand: fix build error with ARMv4
Message-ID: <20170804093240.25753a23@bbrezillon>
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On Fri, 21 Jul 2017 22:38:06 +0200
Arnd Bergmann <arnd@arndb.de> wrote:

> orion_nand_read_buf uses an inline assembly with the "ldrd"
> instruction, which is only available from ARMv5 upwards. This
> used to be fine, since all users have an ARMv5 or ARMv7 CPU,
> but now we can also build a multiplatform kernel with ARMv4
> support enabled in addition to the "kirkwood" (mvebu) platform.
> 
> This provides an alternative to call the readsl() function that
> is supposed to have the same effect and is also optimized for
> performance.
> 
> I first posted a version of this patch back in 2014, and there
> was some discussion about it then. This fixes the bugs identified
> back then and should be a reasonable alternative for the rare
> corner case.

Looks good to me. Applied to nand/next. Let's see if anyone complains
before the merge window.

Thanks,

Boris

> 
> Link: https://patchwork.kernel.org/patch/4144791/
> Cc: Jingoo Han <jg1.han@samsung.com>
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/mtd/nand/orion_nand.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/drivers/mtd/nand/orion_nand.c b/drivers/mtd/nand/orion_nand.c
> index 209170ed2b76..41cb7acfc044 100644
> --- a/drivers/mtd/nand/orion_nand.c
> +++ b/drivers/mtd/nand/orion_nand.c
> @@ -54,13 +54,16 @@ static void orion_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
>  {
>  	struct nand_chip *chip = mtd_to_nand(mtd);
>  	void __iomem *io_base = chip->IO_ADDR_R;
> +#if __LINUX_ARM_ARCH__ >= 5
>  	uint64_t *buf64;
> +#endif
>  	int i = 0;
>  
>  	while (len && (unsigned long)buf & 7) {
>  		*buf++ = readb(io_base);
>  		len--;
>  	}
> +#if __LINUX_ARM_ARCH__ >= 5
>  	buf64 = (uint64_t *)buf;
>  	while (i < len/8) {
>  		/*
> @@ -74,6 +77,10 @@ static void orion_nand_read_buf(struct mtd_info *mtd, uint8_t *buf, int len)
>  		buf64[i++] = x;
>  	}
>  	i *= 8;
> +#else
> +	readsl(io_base, buf, len/4);
> +	i = len / 4 * 4;
> +#endif
>  	while (i < len)
>  		buf[i++] = readb(io_base);
>  }