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

From: Brian Norris
Date: Tue Apr 05 2016 - 14:14:43 EST


+ 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@xxxxxx>
> ---

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