linux-kernel - Re: [RESEND][PATCH] mtd: devices: m25p80: add support for mmap read request

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Date:	Wed, 18 May 2016 11:23:35 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Vignesh R <vigneshr@...com>
Cc:	Brian Norris <computersforpeace@...il.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	David Woodhouse <dwmw2@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RESEND][PATCH] mtd: devices: m25p80: add support for mmap read request

Hello,

On 29 March 2016 at 07:46, Vignesh R <vigneshr@...com> wrote:
> Certain SPI controllers may provide accelerated hardware interface to
> read from m25p80 type flash devices in order to provide better read
> performance. SPI core supports such devices with spi_flash_read() API.
> Call spi_flash_read(), if supported, to make use of such interface.
>
> Signed-off-by: Vignesh R <vigneshr@...com>
> ---
>
> Resend v5:
> Rebased on top of v4.6-rc1
> v5: http://www.spinics.net/lists/devicetree/msg106696.html
>
>  drivers/mtd/devices/m25p80.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
>
> diff --git a/drivers/mtd/devices/m25p80.c b/drivers/mtd/devices/m25p80.c
> index c9c3b7fa3051..7730e633d7d3 100644
> --- a/drivers/mtd/devices/m25p80.c
> +++ b/drivers/mtd/devices/m25p80.c
> @@ -131,6 +131,26 @@ static int m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
>         /* convert the dummy cycles to the number of bytes */
>         dummy /= 8;
>
> +       if (spi_flash_read_supported(spi)) {
> +               struct spi_flash_read_message msg;
> +               int ret;
> +
> +               msg.buf = buf;
> +               msg.from = from;
> +               msg.len = len;
> +               msg.read_opcode = nor->read_opcode;
> +               msg.addr_width = nor->addr_width;
> +               msg.dummy_bytes = dummy;
> +               /* TODO: Support other combinations */
> +               msg.opcode_nbits = SPI_NBITS_SINGLE;
> +               msg.addr_nbits = SPI_NBITS_SINGLE;
> +               msg.data_nbits = m25p80_rx_nbits(nor);
> +
> +               ret = spi_flash_read(spi, &msg);
> +               *retlen = msg.retlen;

This is wrong. The previous retlen is never passed into msg so it must
be added and not assigned as is seen a few lines below:

        ret = m.actual_length - m25p_cmdsz(nor) - dummy;
        if (ret < 0)
                return -EIO;
        *retlen += ret;

This interface with odd design and poor documentation will be
hopefully weeded out with
mtd: spi-nor: stop passing around retlen
so there is probably no need to patch this separately.

Thanks

Michal