I've looked a bit on the Triton chipset and I noticed that it's possible
to control memory mapping in the 0xC0000-0xFFFFF region (other PCI chipsets
are usually also capable of such things, but I'll look at them later). I've
written a very experimental patch filling the whole region with RAM
(throwing out all BIOSes) and thus gaining 256K (additional 4K come from
the 0x9C000 page which needn't to be reserved in such cases).
This patch breaks:
- PCI BIOS access (completely disabled by the patch and direct HW access
is used instead => everything should work well)
- APM
- Rebooting thru BIOS
Look at it, test it, do anything you want with it...
Current plans what to do next: write generic chipset support for Linux
allowing other extensions to be used (32-bit DMA addressing and so on)...
Good luck
Martin
--- arch/i386/mm/init.c.old Tue May 6 19:15:07 1997
+++ arch/i386/mm/init.c Tue May 6 19:20:05 1997
@@ -26,6 +26,7 @@
#include <asm/uaccess.h>
#include <asm/pgtable.h>
#include <asm/dma.h>
+#include <asm/io.h>
const char bad_pmd_string[] = "Bad pmd in pte_alloc: %08lx\n";
@@ -292,6 +293,7 @@
#endif
start_mem = PAGE_ALIGN(start_mem);
+#ifdef NO_DIRTY_MM_TRICKS_FOR_TRITON
/*
* IBM messed up *AGAIN* in their thinkpad: 0xA0000 -> 0x9F000.
* They seem to have done something stupid with the floppy
@@ -301,6 +303,29 @@
clear_bit(PG_reserved, &mem_map[MAP_NR(start_low_mem)].flags);
start_low_mem += PAGE_SIZE;
}
+#else
+ /*
+ * These hacks are only for Intel Triton chipsets, so we don't
+ * expect any odd ThinkPad behaviour.
+ */
+ while (start_low_mem < 0xa0000+PAGE_OFFSET) {
+ clear_bit(PG_reserved, &mem_map[MAP_NR(start_low_mem)].flags);
+ start_low_mem += PAGE_SIZE;
+ }
+ save_flags(tmp); /* Mark 0xc0000-0xcffff as readable, writeable and
cacheable */
+ cli();
+ outl(0x80000058, 0xcf8);
+ outl((inl(0xcfc) & 0x000000ff) | 0x77777000, 0xcfc);
+ outl(0x8000005c, 0xcf8);
+ outl(0x77777777, 0xcfc);
+ outl(0, 0xcf8);
+ restore_flags(tmp);
+ start_low_mem = PAGE_OFFSET + 0xc0000; /* And add them to the memory
pool */
+ while (start_low_mem < 0x100000+PAGE_OFFSET) {
+ clear_bit(PG_reserved, &mem_map[MAP_NR(start_low_mem)].flags);
+ start_low_mem += PAGE_SIZE;
+ }
+#endif
while (start_mem < end_mem) {
clear_bit(PG_reserved, &mem_map[MAP_NR(start_mem)].flags);
--- arch/i386/kernel/bios32.c.old Tue May 6 19:46:59 1997
+++ arch/i386/kernel/bios32.c Tue May 6 19:51:35 1997
@@ -889,6 +889,7 @@
*
*/
+#ifdef NO_DIRTY_MM_TRICKS_FOR_TRITON
for (check = (union bios32 *) __va(0xe0000);
check <= (union bios32 *) __va(0xffff0);
++check) {
@@ -921,6 +922,12 @@
}
if (bios32_entry && check_pcibios())
access_pci = &pci_bios_access;
+#else
+ /* We must disable PCI BIOS support for the Triton MM hack,
+ * but we can simply use direct access instead.
+ */
+ access_pci = check_direct_pci();
+#endif
#endif
return memory_start;
}