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Diffstat (limited to 'Documentation/driver-api/mtd/spi-nor.rst')
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diff --git a/Documentation/driver-api/mtd/spi-nor.rst b/Documentation/driver-api/mtd/spi-nor.rst new file mode 100644 index 000000000000..f5333e3bf486 --- /dev/null +++ b/Documentation/driver-api/mtd/spi-nor.rst @@ -0,0 +1,66 @@ +================= +SPI NOR framework +================= + +Part I - Why do we need this framework? +--------------------------------------- + +SPI bus controllers (drivers/spi/) only deal with streams of bytes; the bus +controller operates agnostic of the specific device attached. However, some +controllers (such as Freescale's QuadSPI controller) cannot easily handle +arbitrary streams of bytes, but rather are designed specifically for SPI NOR. + +In particular, Freescale's QuadSPI controller must know the NOR commands to +find the right LUT sequence. Unfortunately, the SPI subsystem has no notion of +opcodes, addresses, or data payloads; a SPI controller simply knows to send or +receive bytes (Tx and Rx). Therefore, we must define a new layering scheme under +which the controller driver is aware of the opcodes, addressing, and other +details of the SPI NOR protocol. + +Part II - How does the framework work? +-------------------------------------- + +This framework just adds a new layer between the MTD and the SPI bus driver. +With this new layer, the SPI NOR controller driver does not depend on the +m25p80 code anymore. + +Before this framework, the layer is like:: + + MTD + ------------------------ + m25p80 + ------------------------ + SPI bus driver + ------------------------ + SPI NOR chip + + After this framework, the layer is like: + MTD + ------------------------ + SPI NOR framework + ------------------------ + m25p80 + ------------------------ + SPI bus driver + ------------------------ + SPI NOR chip + + With the SPI NOR controller driver (Freescale QuadSPI), it looks like: + MTD + ------------------------ + SPI NOR framework + ------------------------ + fsl-quadSPI + ------------------------ + SPI NOR chip + +Part III - How can drivers use the framework? +--------------------------------------------- + +The main API is spi_nor_scan(). Before you call the hook, a driver should +initialize the necessary fields for spi_nor{}. Please see +drivers/mtd/spi-nor/spi-nor.c for detail. Please also refer to fsl-quadspi.c +when you want to write a new driver for a SPI NOR controller. +Another API is spi_nor_restore(), this is used to restore the status of SPI +flash chip such as addressing mode. Call it whenever detach the driver from +device or reboot the system. |