[deliverable/linux.git] / Documentation / mtd / spi-nor.txt

                          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.
Commit	Line	Data
1ef39108 HS	1	SPI NOR framework
	2	============================================
	3
	4	Part I - why we need this framework?
	5	-------------------------------------
	6
	7	The SPI bus controller only deals with the byte stream.
	8	Some controller does not works like a SPI bus controller, it works
	9	like a SPI NOR controller instead, such as the Freescale's QuadSPI controller.
	10
	11	The Freescale's QuadSPI controller should know the NOR commands to
	12	find the right LUT sequence. Unfortunately, the old code can not meet
	13	this requirement.
	14
	15	Part II - How does the framework work?
	16	-------------------------------------
	17
	18	This framework just adds a new layer between the MTD and the SPI bus driver.
	19	With this new layer, the SPI NOR controller driver does not depend on the
	20	m25p80 code anymore.
	21
	22	Before this framework, the layer is like:
	23
	24	MTD
	25	------------------------
	26	m25p80
	27	------------------------
	28	SPI bus driver
	29	------------------------
	30	SPI NOR chip
	31
	32	After this framework, the layer is like:
	33	MTD
	34	------------------------
	35	SPI NOR framework
	36	------------------------
	37	m25p80
	38	------------------------
	39	SPI bus driver
	40	------------------------
	41	SPI NOR chip
	42
	43	With the SPI NOR controller driver(Freescale QuadSPI), it looks like:
	44	MTD
	45	------------------------
	46	SPI NOR framework
	47	------------------------
	48	fsl-quadSPI
	49	------------------------
	50	SPI NOR chip
	51
	52	Part III - How can the drivers use the framework
	53	-------------------------------------
	54
	55	The main API is the spi_nor_scan(). Before you call the hook, you should
	56	initialize the necessary fields for spi_nor{}.
	57	Please see the drivers/mtd/spi-nor/spi-nor.c for detail.
	58	Please also reference to the fsl-quadspi.c when you want to write a new driver
	59	for a SPI NOR controller.