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Subject[PATCH] Re: e820 memory detection fix for ThinkPad

David Weinhall wrote:

> On Tue, Dec 19, 2000 at 07:16:40PM -0500, Marc Joosen wrote:
> >
> > This is a tiny patch to make the int15/e820 memory mapping work on
> > ThinkPads. Until now, I have had to give lilo a mem= option with one
> If this simple patch solves your problem, great! But in that case,
> PLEASE add a note telling WHY the assignment is done for every
> iteration; else some smarthead will probably submit a patch someday
> in the future along the lines of "assigning this only once makes the
> loop faster"...
> Anyhow, good spotting!

Thanks for the tip, David. I hope that whoever wants to move that line
out of the loop is aware that it is only executed ~10 times :) So I
hereby submit a second version of the patch, that includes a link to
the documentation and #defines the word SMAP (thanks to David Parsons
for that):

--- linux/arch/i386/boot/setup.S.orig Mon Oct 30 17:44:29 2000
+++ linux/arch/i386/boot/setup.S Thu Dec 21 19:37:12 2000
@@ -289,10 +289,11 @@
# a whole bunch of different types, and allows memory holes and
# everything. We scan through this memory map and build a list
# of the first 32 memory areas, which we return at [E820MAP].
+# This is documented at
+#define SMAP 0x534d4150

- movl $0x534d4150, %edx # ascii `SMAP'
xorl %ebx, %ebx # continuation counter
movw $E820MAP, %di # point into the whitelist
# so we can have the bios
@@ -300,13 +301,15 @@

movl $0x0000e820, %eax # e820, upper word zeroed
+ movl $SMAP, %edx # do this every time, some
+ # bioses are forgetful
movl $20, %ecx # size of the e820rec
pushw %ds # data record.
popw %es
int $0x15 # make the call
jc bail820 # fall to e801 if it fails

- cmpl $0x534d4150, %eax # check the return is `SMAP'
+ cmpl $SMAP, %eax # check the return is `SMAP'
jne bail820 # fall to e801 if it fails

# cmpl $1, 16(%di) # is this usable memory?

Again, please copy any comments to me (, since
I'm not subscribed to linux-kernel.

Marc Joosen
Communication Link Design
IBM T.J. Watson Research Center
Yorktown Heights, NY

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