1================= 2SPI NOR framework 3================= 4 5Part I - Why do we need this framework? 6--------------------------------------- 7 8SPI bus controllers (drivers/spi/) only deal with streams of bytes; the bus 9controller operates agnostic of the specific device attached. However, some 10controllers (such as Freescale's QuadSPI controller) cannot easily handle 11arbitrary streams of bytes, but rather are designed specifically for SPI NOR. 12 13In particular, Freescale's QuadSPI controller must know the NOR commands to 14find the right LUT sequence. Unfortunately, the SPI subsystem has no notion of 15opcodes, addresses, or data payloads; a SPI controller simply knows to send or 16receive bytes (Tx and Rx). Therefore, we must define a new layering scheme under 17which the controller driver is aware of the opcodes, addressing, and other 18details of the SPI NOR protocol. 19 20Part II - How does the framework work? 21-------------------------------------- 22 23This framework just adds a new layer between the MTD and the SPI bus driver. 24With this new layer, the SPI NOR controller driver does not depend on the 25m25p80 code anymore. 26 27Before this framework, the layer is like:: 28 29 MTD 30 ------------------------ 31 m25p80 32 ------------------------ 33 SPI bus driver 34 ------------------------ 35 SPI NOR chip 36 37After this framework, the layer is like:: 38 39 MTD 40 ------------------------ 41 SPI NOR framework 42 ------------------------ 43 m25p80 44 ------------------------ 45 SPI bus driver 46 ------------------------ 47 SPI NOR chip 48 49With the SPI NOR controller driver (Freescale QuadSPI), it looks like:: 50 51 MTD 52 ------------------------ 53 SPI NOR framework 54 ------------------------ 55 fsl-quadSPI 56 ------------------------ 57 SPI NOR chip 58 59Part III - How can drivers use the framework? 60--------------------------------------------- 61 62The main API is spi_nor_scan(). Before you call the hook, a driver should 63initialize the necessary fields for spi_nor{}. Please see 64drivers/mtd/spi-nor/spi-nor.c for detail. Please also refer to spi-fsl-qspi.c 65when you want to write a new driver for a SPI NOR controller. 66Another API is spi_nor_restore(), this is used to restore the status of SPI 67flash chip such as addressing mode. Call it whenever detach the driver from 68device or reboot the system. 69