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dm: doc: Update description of pre-relocation support

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Add some description about pre-relocation driver binding, including
usage of DM_FLAG_PRE_RELOC flag and caveats.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Bin Meng 2018-10-24 06:36:40 -07:00 committed by Simon Glass
parent 8ee27da343
commit 1a6bd4717f
1 changed files with 12 additions and 4 deletions
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16
doc/driver-model/README.txt
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@ -830,10 +830,18 @@ Pre-Relocation Support
----------------------
For pre-relocation we simply call the driver model init function. Only
drivers marked with DM_FLAG_PRE_RELOC or the device tree
'u-boot,dm-pre-reloc' flag are initialised prior to relocation. This helps
to reduce the driver model overhead. This flag applies to SPL and TPL as
well, if device tree is enabled there.
drivers marked with DM_FLAG_PRE_RELOC or the device tree 'u-boot,dm-pre-reloc'
property are initialised prior to relocation. This helps to reduce the driver
model overhead. This flag applies to SPL and TPL as well, if device tree is
enabled (CONFIG_OF_CONTROL) there.
Note when device tree is enabled, the device tree 'u-boot,dm-pre-reloc'
property can provide better control granularity on which device is bound
before relocation. While with DM_FLAG_PRE_RELOC flag of the driver all
devices with the same driver are bound, which requires allocation a large
amount of memory. When device tree is not used, DM_FLAG_PRE_RELOC is the
only way for statically declared devices via U_BOOT_DEVICE() to be bound
prior to relocation.
It is possible to limit this to specific relocation steps, by using
the more specialized 'u-boot,dm-spl' and 'u-boot,dm-tpl' flags