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dm: core: Add documentation about device removal

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Make mention of this feature in the core documentation so people can
discover it without looking at a header file.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2021-01-24 14:32:48 -07:00
parent 6224dc9ba4
commit 7a3c628c43
1 changed files with 20 additions and 0 deletions
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20
doc/driver-model/design.rst
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@ -880,6 +880,26 @@ If a parent has children these will be destroyed first. After this point
the device does not exist and its memory has be deallocated.
Special cases for removal
-------------------------
Some devices need to do clean-up before the OS is called. For example, a USB
driver may want to stop the bus. This can be done in the remove() method.
Some special flags are used to determine whether to remove the device:
DM_FLAG_OS_PREPARE - indicates that the device needs to get ready for OS
boot. The device will be removed just before the OS is booted
DM_REMOVE_ACTIVE_DMA - indicates that the device uses DMA. This is
effectively the same as DM_FLAG_OS_PREPARE, so the device is removed
before the OS is booted
DM_FLAG_VITAL - indicates that the device is 'vital' to the operation of
other devices. It is possible to remove this device after all regular
devices are removed. This is useful e.g. for a clock, which need to
be active during the device-removal phase.
The dm_remove_devices_flags() function can be used to remove devices based on
their driver flags.
Data Structures
---------------