Re: [PATCH 1/5] spi: introduce mmap read support for spi flash devices

Jagan Teki
2015-09-04T11:25:33Z

On 4 September 2015 at 13:59, Vignesh R <vigneshr@ti.com> wrote:
> In addition to providing direct access to SPI bus, some spi controller
> hardwares (like ti-qspi) provide special memory mapped port
> to accesses SPI flash devices in order to increase read performance.
> This means the controller can automatically send the SPI signals
> required to read data from the SPI flash device.
> For this, spi controller needs to know flash specific information like
> read command to use, dummy bytes and address width. Once these settings
> are populated in hardware registers, any read accesses to flash's memory
> map region(SoC specific) through memcpy or mem-to-mem DMA copy will be
> handled by controller hardware. The hardware will automatically generate
> spi signals required to read data from flash and present it to CPU or
> DMA engine.
>
> Introduce spi_mtd_mmap_read() method to support memory mapped read
> over SPI flash devices. SPI master drivers can implement this method to
> support memory mapped read interfaces. m25p80 flash driver and other
> flash drivers can call this to request memory mapped read. The interface
> should only be used mtd flashes and cannot be used with other spi devices.
>
> Signed-off-by: Vignesh R <vigneshr@ti.com>
> ---
> include/linux/spi/spi.h | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
>
> diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
> index d673072346f2..b74a3f169fc2 100644
> --- a/include/linux/spi/spi.h
> +++ b/include/linux/spi/spi.h
> @@ -293,6 +293,23 @@ static inline void spi_unregister_driver(struct spi_driver *sdrv)
> * @handle_err: the subsystem calls the driver to handle an error that occurs
> * in the generic implementation of transfer_one_message().
> * @unprepare_message: undo any work done by prepare_message().
> + * @spi_mtd_mmap_read: some spi-controller hardwares provide memory
> + * mapped interface to communicate with mtd flashes.
> + * For this, spi controller needs to know flash
> + * memory settings like read command to use, dummy
> + * bytes and address width. Once these settings are
> + * populated in hardware registers, any read
> + * accesses to flash's memory map region(as defined
> + * by SoC) through memcpy or mem-to-mem DMA copy
> + * will be handled by controller hardware. The
> + * hardware will automatically generate spi signals
> + * required to read data from flash and present it
> + * to CPU or DMA. SPI master drivers can use this
> + * callback to implement memory mapped read
> + * interface. Flash driver (like m25p80) requests
> + * memory mapped read via this method. The interface
> + * should only be used mtd flashes and cannot be
> + * used with other spi devices.
> * @cs_gpios: Array of GPIOs to use as chip select lines; one per CS
> * number. Any individual value may be -ENOENT for CS lines that
> * are not GPIOs (driven by the SPI controller itself).
> @@ -438,6 +455,10 @@ struct spi_master {
> struct spi_message *message);
> int (*unprepare_message)(struct spi_master *master,
> struct spi_message *message);
> + int (*spi_mtd_mmap_read)(struct spi_device *spi,
> + loff_t from, size_t len, size_t *retlen,
> + u_char *buf, u8 read_opcode,
> + u8 addr_width, u8 dummy_bytes);

This looks un-manageable to know spi core or master knows what are the
command or opcode used by spi-nor flash and also I think mmap support
seems to be flash related or any justification this is spi bus
master/controller feature?

thanks!
--
Jagan | openedev.