I'm desperately trying to make Linux use int 0x15/eax=0xE820 instead of
0x15/0xE801 (if available) to detect the RAM. Two reasons for this, first
to get rid of the "mem=" boot parameters when RAM is > 64Mb (might already
be gone in the recent 2.1.x), second and most important, because I don't
want Linux to clobber the ACPI table area, at least until I could parse it
safe.
I have two problems :
* Now I can talk to the BIOS and get the SMAP correctly, but I don't see
where I could pass this information from arch/i386/boot/setup.S to
arch/i386/kernel/setup.c (I tried places such as 0x0FE00, (PARAM + 1024)
(obviously a wrong one once I RTFM'ed Doc/i386/zero*.txt...), ( (PARAM +
2048 + 64) and reducing the cmdline buffer to 64 bytes, ...).
My current system needs about 192 bytes to report the system memory
address map, I think a 1 kbyte buffer would be quite safe a value. But
where ? (Is the code from setup.S still visible early in setup_arch ?
Would reserving a 1k buffer in setup.S and writing there do the trick ?
Would it be safe for me to use data over (PARAM + 0x900), since the
command line is supposed to be under 256 bytes ?)
* Once I get a nice map of the memory, I'll get several sparse blocks of
usable memory, with blocks of reserved stuff (ROM, ACPI, ACPI/NVS etc...)
inside, which I'll want to skip.
Is mem_init() in arch/i386/mm/init.c the right place to play with ?
(basically, I'd do something like :
while (start_mem < end_mem) {
+ if (!reserved_by_the_bios(start_mem,PAGE_SIZE)) {
clear_bit(PG_reserved,
&mem_map[MAP_NR(start_mem)].flags);
start_mem += PAGE_SIZE;
+ }
}
Would that work ? (actually, getting away with start_low_mem and
start_mem, and looping through the list of available memory runs as given
by the BIOS could be an even better idea)
(additionally, the ACPI "RSD PTR " table scan looks very similar to the
smp_scan_config() which takes place in the #ifdef __SMP__ block in
paging_init(). Should I do a similar acpi_scan_rsd() there too, before
that memory is remapped away, or can I do it later (at module
initialisation, for instance) ?.
Finally, is clearing the PG_reserved bit in the ACPI memory pages
(after I copy them away) enough to let the MM subsystem use them ?
Thank you very much in advance
-- Cyrille
------------------------------
Je me demande pourquoi les gens me regardent comme ēa, dans le RER...
les cheveux bleus, sūrement !
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