Re: memory barrier to ensure copy_to_user() completes
- From: Alan Cox <alan@xxxxxxxxxxxxxxxxxxx>
- Date: Fri, 31 Aug 2007 17:08:07 +0100
Which memory barrier do I require if I need to ensure that a
copy_to_user(dest, src, len) completes before the next statement?
Define "completes"
copy_to_user(dest, src, len) ;
//rmb(); OR wmb(); OR barrier(); OR mb(); ??????
Usually none of them
If I'm writing to hardware, and need to ensure the correct order, I'll
use wmb(), right?
No
e.g.:
#define HW_address1 20
#define HW_address2 40
*((int *)HW_address1) = 0x00000001;
wmb(); // is this good???
*((int *)HW_address2) = 0x00000010;
Linux doesn't define directly poking kernel addresses to hit hardware as
valid (and on many platforms it doesn't work). Use readl/writel and their
ordering is defined.
Read Documentation/io_ordering.txt and Docuemntation/pci.txt
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