[U-Boot-Users] pci auto allocate region problem?

[xianghui ren]

hello, everybody:
In pciauto_region_allocate function, I can't  understand the mean of  the
sentence "addr = ((res->bus_lower - 1) | (size - 1)) + 1;".
why to do "-1" and "+1" operate?
why to do or operate?
What does the variable "addr" mean?

Thanks in advance!
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