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


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