mmap() file operations and changing vm_start
From: sam (sam_at_here.com)
Date: 03/30/05
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Date: Tue, 29 Mar 2005 19:42:14 -0500
I am working on an embedded board running linux 2.4.28. I 've got a
driver module written that provides access to I/O and reserved memory.
I have noticed that user mmap() calls handled in my mmap() file operations
routine return a one-to-one mapping (between virtual and physical addresses)
for some addresses but not for others.
<= 0x9000 0000 -- one to one
>= 0xa000 0000 -- NON one to one
I thought about modifying the "vm_start" parameter but I dont think thats a
"safe" hack. MAP_FIXED returns an error message and doesnt even enter my
mmap() file operations routine.
I am currently re-reading the mmap and dma section of the linux device driver
manual but I would like pointers on a way around this.
Note the physical address I am trying get at : 0xb000 0000 isnt in conflict ...
meaning there arent any virtual addresss allocated between 0xb000 0000 and
0xbfff ffff so I should be able to get at this.
But the "vm_start" argument i am passed is consistently a virtual address
below this value.
Thanks in advance
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