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Diffstat (limited to 'doc/driver-model/spi-howto.txt')
| -rw-r--r-- | doc/driver-model/spi-howto.txt | 40 |
1 files changed, 37 insertions, 3 deletions
diff --git a/doc/driver-model/spi-howto.txt b/doc/driver-model/spi-howto.txt index 719dbd5..5bc29ad 100644 --- a/doc/driver-model/spi-howto.txt +++ b/doc/driver-model/spi-howto.txt @@ -3,7 +3,8 @@ How to port a SPI driver to driver model Here is a rough step-by-step guide. It is based around converting the exynos SPI driver to driver model (DM) and the example code is based -around U-Boot v2014.10-rc2 (commit be9f643). +around U-Boot v2014.10-rc2 (commit be9f643). This has been updated for +v2015.04. It is quite long since it includes actual code examples. @@ -262,8 +263,8 @@ U_BOOT_DEVICE(board_spi0) = { .platdata = &platdata_spi0, }; -You will unfortunately need to put the struct into a header file in this -case so that your board file can use it. +You will unfortunately need to put the struct definition into a header file +in this case so that your board file can use it. 9. Add the device private data @@ -592,3 +593,36 @@ board. You can use 'tools/patman/patman' to prepare, check and send patches for your work. See the README for details. + +20. A little note about SPI uclass features: + +The SPI uclass keeps some information about each device 'dev' on the bus: + + struct dm_spi_slave_platdata - this is device_get_parent_platdata(dev) + This is where the chip select number is stored, along with + the default bus speed and mode. It is automatically read + from the device tree in spi_child_post_bind(). It must not + be changed at run-time after being set up because platform + data is supposed to be immutable at run-time. + struct spi_slave - this is device_get_parentdata(dev) + Already mentioned above. It holds run-time information about + the device. + +There are also some SPI uclass methods that get called behind the scenes: + + spi_post_bind() - called when a new bus is bound + This scans the device tree for devices on the bus, and binds + each one. This in turn causes spi_child_post_bind() to be + called for each, which reads the device tree information + into the parent (per-child) platform data. + spi_child_post_bind() - called when a new child is bound + As mentioned above this reads the device tree information + into the per-child platform data + spi_child_pre_probe() - called before a new child is probed + This sets up the mode and speed in struct spi_slave by + copying it from the parent's platform data for this child. + It also sets the 'dev' pointer, needed to permit passing + 'struct spi_slave' around the place without needing a + separate 'struct udevice' pointer. + +The above housekeeping makes it easier to write your SPI driver. |