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

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Date:	Tue, 5 Apr 2016 11:14:27 -0700
From:	Brian Norris <computersforpeace@...il.com>
To:	Vignesh R <vigneshr@...com>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Mark Brown <broonie@...nel.org>,
	Cyrille Pitchen <cyrille.pitchen@...el.com>
Subject: Re: [RESEND][PATCH] mtd: devices: m25p80: add support for mmap read
 request

+ Mark, Cyrille

On Tue, Mar 29, 2016 at 11:16:17AM +0530, Vignesh R 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>
> ---

Applied, with a small diff.

> 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;
> +

I added a memset(&msg, 0, sizeof(msg)), since spi_flash_read() doesn't
guarantee msg.retlen is zeroed for failures. Do we want a
spi_flash_read_message_init() function, to mirror spi_message_init()?

> +		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 */

Speaking of "other combinations": does the TI QSPI controller support
MMAP'ed read modes other than 1/1/{1,2,4}? It doesn't seem to implement
support, and the SPI core doesn't handle this. So if we merge any of
Cyrille's work on other modes, then this is going to break quickly.

> +		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;
> +		return ret;
> +	}
> +
>  	spi_message_init(&m);
>  	memset(t, 0, (sizeof t));
>  

Brian