Based on kernel version 4.16.1. Page generated on 2018-04-09 11:53 EST.
1 SPI NOR framework 2 ============================================ 3 4 Part I - Why do we need this framework? 5 --------------------------------------- 6 7 SPI bus controllers (drivers/spi/) only deal with streams of bytes; the bus 8 controller operates agnostic of the specific device attached. However, some 9 controllers (such as Freescale's QuadSPI controller) cannot easily handle 10 arbitrary streams of bytes, but rather are designed specifically for SPI NOR. 11 12 In particular, Freescale's QuadSPI controller must know the NOR commands to 13 find the right LUT sequence. Unfortunately, the SPI subsystem has no notion of 14 opcodes, addresses, or data payloads; a SPI controller simply knows to send or 15 receive bytes (Tx and Rx). Therefore, we must define a new layering scheme under 16 which the controller driver is aware of the opcodes, addressing, and other 17 details of the SPI NOR protocol. 18 19 Part II - How does the framework work? 20 -------------------------------------- 21 22 This framework just adds a new layer between the MTD and the SPI bus driver. 23 With this new layer, the SPI NOR controller driver does not depend on the 24 m25p80 code anymore. 25 26 Before this framework, the layer is like: 27 28 MTD 29 ------------------------ 30 m25p80 31 ------------------------ 32 SPI bus driver 33 ------------------------ 34 SPI NOR chip 35 36 After this framework, the layer is like: 37 MTD 38 ------------------------ 39 SPI NOR framework 40 ------------------------ 41 m25p80 42 ------------------------ 43 SPI bus driver 44 ------------------------ 45 SPI NOR chip 46 47 With the SPI NOR controller driver (Freescale QuadSPI), it looks like: 48 MTD 49 ------------------------ 50 SPI NOR framework 51 ------------------------ 52 fsl-quadSPI 53 ------------------------ 54 SPI NOR chip 55 56 Part III - How can drivers use the framework? 57 --------------------------------------------- 58 59 The main API is spi_nor_scan(). Before you call the hook, a driver should 60 initialize the necessary fields for spi_nor{}. Please see 61 drivers/mtd/spi-nor/spi-nor.c for detail. Please also refer to fsl-quadspi.c 62 when you want to write a new driver for a SPI NOR controller. 63 Another API is spi_nor_restore(), this is used to restore the status of SPI 64 flash chip such as addressing mode. Call it whenever detach the driver from 65 device or reboot the system.