On Apr 19, 2008, at 6:07 AM, Gerhard Pircher wrote:
-------- Original-Nachricht --------
Datum: Thu, 17 Apr 2008 21:57:05 -0500 (CDT)
Von: Kumar Gala <[EMAIL PROTECTED]>
An: Paul Mackerras <[EMAIL PROTECTED]>
CC: linuxppc-dev@ozlabs.org
Betreff: [PATCH] [POWERPC] Port fixmap from x86 and use for
kmap_atomic
The fixmap code from x86 allows us to have compile time virtual
addresses
that we change the physical addresses of at run time.
...
+/*
+ * Here we define all the compile-time 'special' virtual
+ * addresses. The point is to have a constant address at
+ * compile time, but to set the physical address only
+ * in the boot process. We allocate these special addresses
+ * from the end of virtual memory (0xfffff000) backwards.
+ * Also this lets us do fail-safe vmalloc(), we
+ * can guarantee that these special addresses and
+ * vmalloc()-ed addresses never overlap.
I don't understand how highmem works, but I'm just interested to
know, if
this implementation could conflict somehow with the non coherent DMA
implementation in dma-noncoherent.c (which uses address space from
0xff100000 to 0xff300000 for DMA memory).
if the size is fixed we can easily change it so the Kconfig options
aren't needed anymore.
On the other side could dma-noncoherent.c benefit from fixmaps so
that it
isn't necessary to configure a start address for DMA allocations?
Its possible however the fixmap is all about keeping the VA the same
while changing the PA. I think some work that is being done for the SW
IOMMU might be more useful to your needs.
- k
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