Adrian Cox [off-list ref] wrote:
Yes - and I set ISA_DMA_THRESHOLD to 0x00ffffff. It's not possible to
use ISA DMA with the Via southbridge unless you have main memory at 0x0
on the PCI bus.
As I understand it, you also have to have no I/O hole in the mapping of the
bottom 16 MB of memory onto PCI, right? As I understand it, Linux/PPC is a sane
PPC OS and treats all PPC memory as normal, without any special treatment for
0xA0000-0xFFFFF, so your DMA buffer could legitimately end up in that region
and if your memory map has an I/O hole you would be screwed, right? And of
course main memory on PCI at 0 with no I/O hole means you can't have video on
the same PCI bus... !@#$ing pee sea legacy :(
MS
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Michael Sokolov wrote:
As I understand it, you also have to have no I/O hole in the mapping of the
bottom 16 MB of memory onto PCI, right? As I understand it, Linux/PPC is a sane
PPC OS and treats all PPC memory as normal, without any special treatment for
0xA0000-0xFFFFF, so your DMA buffer could legitimately end up in that region
and if your memory map has an I/O hole you would be screwed, right? And of
course main memory on PCI at 0 with no I/O hole means you can't have video on
the same PCI bus... !@#$ing pee sea legacy :(
I have two CT69030 VGA chips on the same PCI bus, but I only enable
their PCI memory mapped regions, and never use the legacy VGA addresses.
Linux on this board doesn't hand out memory in the 0xa0000 to 0xfffff
region as DMA buffers, because that range is part of the kernel text
segment. Linux on i386 explicity removes that range from the memory
map, and for completeness I should probably ensure that those pages are
marked reserved in case a minimal kernel comes below the 1MB barrier.
--
Adrian Cox http://www.humboldt.co.uk/
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