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author | Linus Torvalds | 2019-07-16 21:21:41 +0200 |
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committer | Linus Torvalds | 2019-07-16 21:21:41 +0200 |
commit | c309b6f24222246c18a8b65d3950e6e755440865 (patch) | |
tree | 11893170f5c246bb0dee8066e85878af04162ab0 /Documentation/driver-api/mtd/spi-nor.rst | |
parent | Merge tag 'xtensa-20190715' of git://github.com/jcmvbkbc/linux-xtensa (diff) | |
parent | docs: kbuild: fix build with pdf and fix some minor issues (diff) | |
download | kernel-qcow2-linux-c309b6f24222246c18a8b65d3950e6e755440865.tar.gz kernel-qcow2-linux-c309b6f24222246c18a8b65d3950e6e755440865.tar.xz kernel-qcow2-linux-c309b6f24222246c18a8b65d3950e6e755440865.zip |
Merge tag 'docs/v5.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media
Pull rst conversion of docs from Mauro Carvalho Chehab:
"As agreed with Jon, I'm sending this big series directly to you, c/c
him, as this series required a special care, in order to avoid
conflicts with other trees"
* tag 'docs/v5.3-1' of git://git.kernel.org/pub/scm/linux/kernel/git/mchehab/linux-media: (77 commits)
docs: kbuild: fix build with pdf and fix some minor issues
docs: block: fix pdf output
docs: arm: fix a breakage with pdf output
docs: don't use nested tables
docs: gpio: add sysfs interface to the admin-guide
docs: locking: add it to the main index
docs: add some directories to the main documentation index
docs: add SPDX tags to new index files
docs: add a memory-devices subdir to driver-api
docs: phy: place documentation under driver-api
docs: serial: move it to the driver-api
docs: driver-api: add remaining converted dirs to it
docs: driver-api: add xilinx driver API documentation
docs: driver-api: add a series of orphaned documents
docs: admin-guide: add a series of orphaned documents
docs: cgroup-v1: add it to the admin-guide book
docs: aoe: add it to the driver-api book
docs: add some documentation dirs to the driver-api book
docs: driver-model: move it to the driver-api book
docs: lp855x-driver.rst: add it to the driver-api book
...
Diffstat (limited to 'Documentation/driver-api/mtd/spi-nor.rst')
-rw-r--r-- | Documentation/driver-api/mtd/spi-nor.rst | 66 |
1 files changed, 66 insertions, 0 deletions
diff --git a/Documentation/driver-api/mtd/spi-nor.rst b/Documentation/driver-api/mtd/spi-nor.rst new file mode 100644 index 000000000000..f5333e3bf486 --- /dev/null +++ b/Documentation/driver-api/mtd/spi-nor.rst @@ -0,0 +1,66 @@ +================= +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. +Another API is spi_nor_restore(), this is used to restore the status of SPI +flash chip such as addressing mode. Call it whenever detach the driver from +device or reboot the system. |