Re: Compaq Presario "reboot" problems

[linux-os (Dick Johnson)]

On Fri, 18 Nov 2005, Denis Vlasenko wrote:

> On Thursday 17 November 2005 20:51, linux-os (Dick Johnson) wrote:
>>
>> With Linux-2.4.26 I reported that if a Compaq gets rebooted while
>> running Linux-2.4.26, it will not be able to restart Windows 2000.
>> It cam restart Linux fine. Today, I tried the same thing with
>> Linux-2.6.13.4. It fails, too.
>>
>> The symptoms are that you just "reboot" Linux. When the GRUB loader
>> comes up, I select my Windows-2000/professional. That M$ Crap comes
>> up to where it's just about to start the high-resolution screen.
>> Then it stops forever, no interrupts, no nothing. I need to disconnect
>> power and remove the battery to recover.
>>
>> It appears as though Linux is still restarting as a "warm boot",
>> rather than a cold boot (in other words, putting magic in the
>> shutdown byte of CMOS) so the hardware doesn't get properly
>> initialized. Would somebody please check this out. When changing
>> operating systems, you need a cold-boot.
>
> Can you check which driver does that? The test would be to
> boot a special Linux setup which reboots immediately
> (say, wuth init=/some/reboot_script.sh boot param).
>
> Then start removing drivers from kernel until you
> can boot Win successfully after Linux reboots.
> --
> vda

I booted into a shell from a floppy disk. There were no drivers
installed, not even the IDE driver. I could not reboot windows
after linux was up and rebooted. This was Linux-2.6.13.4. Then
I tried linux-2.4.26 which corresponds to the version when I
first reported this problem. The same thing happens. Therefore,
I temporarily modified linux-2.6.13.4 to force a triple-fault
and processor reset when doing a reboot. With this temporary
modification it is possible to boot windows after Linux was
running.

This is the reboot patch. It is not a "solution", just something
that shows that the current reboot code doesn't force the BIOS
to start from scratch, which is essential when changing operating
systems.


--- linux-2.6.13.4/arch/i386/kernel/reboot.c.orig	2005-11-18 08:29:12.000000000 -0500
+++ linux-2.6.13.4/arch/i386/kernel/reboot.c	2005-11-18 08:52:40.000000000 -0500
@@ -337,6 +337,11 @@

  void machine_restart(char * __unused)
  {
+        for(;;) {
+	__asm__ __volatile__("\tmovl %cr0, %eax\n"
+			     "\tandl $~0x80000000,  %eax\n"
+			     "\tmovl %eax, %cr0\n");
+        }
  	machine_shutdown();
  	machine_emergency_restart();
  }

Just in case the M$ mailer screws up everything, the patch
is attached also.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.13.4 on an i686 machine (5589.54 BogoMips).
Warning : 98.36% of all statistics are fiction.
.


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Thank you.--- linux-2.6.13.4/arch/i386/kernel/reboot.c.orig	2005-11-18 08:29:12.000000000 -0500
+++ linux-2.6.13.4/arch/i386/kernel/reboot.c	2005-11-18 08:52:40.000000000 -0500
@@ -337,6 +337,11 @@
 
 void machine_restart(char * __unused)
 {
+        for(;;) {
+	__asm__ __volatile__("\tmovl %cr0, %eax\n"
+			     "\tandl $~0x80000000,  %eax\n"
+			     "\tmovl %eax, %cr0\n");
+        }
 	machine_shutdown();
 	machine_emergency_restart();
 }