mirror of
https://github.com/torvalds/linux
synced 2024-11-05 18:23:50 +00:00
254592db61
Signed-off-by: Brian Norris <computersforpeace@gmail.com> Reviewed-by: Marek Vasut <marex@denx.de>
62 lines
2.3 KiB
Text
62 lines
2.3 KiB
Text
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.
|