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authorBrian Norris <computersforpeace@gmail.com>2014-04-08 20:17:04 -0700
committerBrian Norris <computersforpeace@gmail.com>2014-04-14 11:23:01 -0700
commit254592db612aeb55d80399a04995b68f7da48c99 (patch)
treeb123f4ff44d473400578363cd9cdb8a9a780c51f /Documentation/mtd
parent58b89a1f4c2a65b10b8f7b90b6ff2161b19bb0d1 (diff)
Documentation: spi-nor: rewrite some portions
Signed-off-by: Brian Norris <computersforpeace@gmail.com> Reviewed-by: Marek Vasut <marex@denx.de>
Diffstat (limited to 'Documentation/mtd')
-rw-r--r--Documentation/mtd/spi-nor.txt37
1 files changed, 20 insertions, 17 deletions
diff --git a/Documentation/mtd/spi-nor.txt b/Documentation/mtd/spi-nor.txt
index 294d5b06f892..548d6306ebca 100644
--- a/Documentation/mtd/spi-nor.txt
+++ b/Documentation/mtd/spi-nor.txt
@@ -1,19 +1,23 @@
SPI NOR framework
============================================
-Part I - why we need this framework?
--------------------------------------
+Part I - Why do 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.
+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.
-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.
+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
@@ -40,7 +44,7 @@ m25p80 code anymore.
------------------------
SPI NOR chip
- With the SPI NOR controller driver(Freescale QuadSPI), it looks like:
+ With the SPI NOR controller driver (Freescale QuadSPI), it looks like:
MTD
------------------------
SPI NOR framework
@@ -49,11 +53,10 @@ m25p80 code anymore.
------------------------
SPI NOR chip
-Part III - How can the drivers use the framework
--------------------------------------
+Part III - How can 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.
+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.

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