>
> Since you're running on an RM9000 class CPU, why don't just use a
64-bit
> kernel? Highmem is just so f*cking insane that you want to avoid it
like
> French kisses from a zombie suffering ebola. If you have DMA
restrictions
> then you may consider reusing ZONE_DMA.
[Anoop P.A.] I understand that I am working on 64 bit kernel in
parallel, DMA issue made me concentrate on highmem support as immediate
option.
> small 32-bit system that didn't need highmem or went 64-bit right away
so
> the gaps in the code while well known were never fixed up ...
[Anoop P.A.] I presume with decreased value of RAM, more 32 bit machines
will come with bulk of memory pretty soon to the world of highmem
>
> I'm a bit surprised that the patch posted actually made things work
better
> for you since it entirely avoids flushing of highmem pages. The code
as
> it
> was originally written using page_address() will perform cacheflushes
> for highmem pages as well - but only for highmem pages are actually
are
> mapped. That is your code will flush less pages than the existing
code.
[Anoop P.A.] I confirmed it, calling __dma_sync for highmem map address
occasionally causes memory corruption ( reports bus error , segmentation
fault etc..) .
Blowing entire scache (I understand it is pain) for highmem pages fixed
my file corruption issue
--- linux-2.6.18/arch/mips/mm/dma-noncoherent.c 2006-08-23
23:16:07.000000000 +0530
+++ linux-2.6.18/arch/mips/mm/dma-noncoherent.c 2010-08-06
20:48:36.000000000 +0530
@@ -15,6 +15,7 @@
#include <asm/cache.h>
#include <asm/io.h>
+#include <asm/r4kcache.h>
/*
* Warning on the terminology - Linux calls an uncached area coherent;
@@ -131,13 +132,21 @@
for (i = 0; i < nents; i++, sg++) {
unsigned long addr;
+ if (!PageHighMem(sg->page))
+ {
+ addr = (unsigned
long)page_address(sg->page) + sg->offset;
+ __dma_sync(addr, sg->length, direction);
+ }
+ else
+ {
+ /*blasting entire cache for all the highmem page's might
be over head
+ But __dma_sync is failing for mapped highmem pages, so
this is the
+ easiest solution for time being*/
+ blast_scache32(); /*RM9000 sc_line=32 */
+ }
- addr = (unsigned long) page_address(sg->page);
- if (addr) {
- __dma_sync(addr + sg->offset, sg->length,
direction);
- sg->dma_address =
(dma_addr_t)page_to_phys(sg->page)
+ sg->dma_address = (dma_addr_t)page_to_phys(sg->page)
+ sg->offset;
- }
}
return nents;
Thanks
Anoop
