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Documentation: add the document for the SPI NOR framework

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This patch adds the document for the SPI NOR framework.

Signed-off-by: Huang Shijie <b32955@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
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Huang Shijie 2014-02-28 15:58:00 +08:00 committed by Brian Norris
parent b199489d37
commit 1ef391084b
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Documentation/mtd/spi-nor.txt Normal file
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SPI NOR framework
============================================
Part I - why we need this framework?
-------------------------------------
The SPI bus controller only deals with the byte stream.
Some controller does not works like a SPI bus controller, it works
like a SPI NOR controller instead, such as the Freescale's QuadSPI controller.
The Freescale's QuadSPI controller should know the NOR commands to
find the right LUT sequence. Unfortunately, the old code can not meet
this requirement.
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 the drivers use the framework
-------------------------------------
The main API is the spi_nor_scan(). Before you call the hook, you should
initialize the necessary fields for spi_nor{}.
Please see the drivers/mtd/spi-nor/spi-nor.c for detail.
Please also reference to the fsl-quadspi.c when you want to write a new driver
for a SPI NOR controller.