linux-kernel - Re: [PATCH] mtd: m25p80: consider max message size in m25p80_read when use the spi_mem

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Date:   Thu, 16 Aug 2018 08:33:07 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Chuanhua Han <chuanhua.han@....com>
Cc:     dwmw2@...radead.org, computersforpeace@...il.com,
        marek.vasut@...il.com, richard@....at, cyrille.pitchen@...ev4u.fr,
        broonie@...nel.org, pp@...ix.com, Zhiqiang.Hou@....com,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mtd: m25p80: consider max message size in m25p80_read
 when use the spi_mem_xx() API

Hi Chuanhua,

On Wed, 15 Aug 2018 14:33:43 +0800
Chuanhua Han <chuanhua.han@....com> wrote:

> Consider a message size limit when calculating the maximum amount
> of data that can be read.
> 
> Signed-off-by: Chuanhua Han <chuanhua.han@....com>
> ---
>  drivers/mtd/devices/m25p80.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index e84563d..87efa56 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -128,7 +128,12 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
>  	op.dummy.nbytes = (nor->read_dummy * op.dummy.buswidth) / 8;
>  
>  	while (remaining) {
> -		op.data.nbytes = remaining < UINT_MAX ? remaining : UINT_MAX;
> +		op.data.nbytes = min3(remaining,
> +				spi_max_transfer_size(flash->spimem->spi),
> +				spi_max_message_size(flash->spimem->spi) -
> +				sizeof(op.cmd.opcode) -
> +				op.addr.nbytes -
> +				op.dummy.nbytes);

Nope, this sort of things should go in the SPI controller driver
->adjust_op_size() hook or directly in spi_mem_adjust_op_size() if it's
generic enough (which doesn't seem to be the case since your not
counting the opcode, addr and dummy bytes in the message length).

Regards,

Boris