linux-kernel - Re: [PATCH v3 34/37] mtd: nand: allow drivers to request minimum alignment for passed buffer

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Date:   Fri, 31 Mar 2017 13:01:03 +0900
From:   Masahiro Yamada <yamada.masahiro@...ionext.com>
To:     linux-mtd@...ts.infradead.org
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        David Woodhouse <dwmw2@...radead.org>,
        Marek Vasut <marek.vasut@...il.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>,
        Graham Moore <grmoore@...nsource.altera.com>,
        Enrico Jorns <ejo@...gutronix.de>,
        Chuanxiao Dong <chuanxiao.dong@...el.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Jassi Brar <jaswinder.singh@...aro.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>
Subject: Re: [PATCH v3 34/37] mtd: nand: allow drivers to request minimum
 alignment for passed buffer

Hi Boris,


2017-03-30 17:15 GMT+09:00 Masahiro Yamada <yamada.masahiro@...ionext.com>:
> In some cases, nand_do_{read,write}_ops is passed with unaligned
> ops->datbuf.  Drivers using DMA will be unhappy about unaligned
> buffer.
>
> The new struct member, buf_align, represents the minimum alignment
> the driver require for the buffer.  If the buffer passed from the
> upper MTD layer does not have enough alignment, nand_do_*_ops will
> use bufpoi.
>
> Signed-off-by: Masahiro Yamada <yamada.masahiro@...ionext.com>
> ---
>
> I was hit by this problem when I ran
>   # mount -t jffs2 /dev/mtdblock*  /mnt
>
> The buffer passed to nand_do_*_ops has 4 byte offset.
> The Denali IP cannot do DMA to/from this buffer because it
> requires 16 byte alignment for DMA.
>
>
> Changes in v3:
>   - Newly added
>
> Changes in v2: None
>
>  drivers/mtd/nand/nand_base.c | 12 ++++++++----
>  include/linux/mtd/nand.h     |  2 ++
>  2 files changed, 10 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/mtd/nand/nand_base.c b/drivers/mtd/nand/nand_base.c
> index e9d3195..b528ffa 100644
> --- a/drivers/mtd/nand/nand_base.c
> +++ b/drivers/mtd/nand/nand_base.c
> @@ -1953,9 +1953,10 @@ static int nand_do_read_ops(struct mtd_info *mtd, loff_t from,
>
>                 if (!aligned)
>                         use_bufpoi = 1;
> -               else if (chip->options & NAND_USE_BOUNCE_BUFFER)
> -                       use_bufpoi = !virt_addr_valid(buf);
> -               else
> +               else if (chip->options & NAND_USE_BOUNCE_BUFFER) {
> +                       use_bufpoi = !virt_addr_valid(buf) ||
> +                              !IS_ALIGNED((unsigned long)buf, chip->buf_align);
> +               } else
>                         use_bufpoi = 0;


I noticed I added unneeded braces here by mistake.
(When I was testing this part, I inserted printk here,
then I forgot to remove the {} . )

Can you fix-up it?

If requested, I can re-send it.





-- 
Best Regards
Masahiro Yamada