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
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doc/driver-model/README.txt | 16 ++++++++++++---- 1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/doc/driver-model/README.txt b/doc/driver-model/README.txt index 3654163..07b120d 100644 --- a/doc/driver-model/README.txt +++ b/doc/driver-model/README.txt @@ -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