[PATCH] use ljmp to reboot (Re: at_keyboard flush on i386-qemu)

[Robert Millan <rmh@aybabtu.com>]

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On Sat, Jun 27, 2009 at 01:25:21PM +0200, Robert Millan wrote:
> 
> Hi,
> 
> Pavel pointed out earlier that sometimes when starting on i386-qemu GRUB
> receives spurious events from AT keyboard.  It seems that it is the role
> of the firmware to flush this buffer at startup.
> 
> Unless someone has a better idea, I would fix this with:
> 
>   - Moving at_keyboard to kernel on i386-qemu.
> 
>   - [ifdef GRUB_MACHINE_QEMU]: flush the input buffer at at_keyboard
>     startup by reading and discarding events for a fixed amount of time.
> 
> I don't like that we have a race here.  Suggestions welcome on how to
> improve that, but TTBOMK if there's more than one event you can't tell
> when you're processing the last one.

Actually I diagnosed this completely wrong.  The real problem is we're
using the keyboard to reboot the machine, which (at least on QEMU) results
in spurious keys being put in the buffer.

I think we should just jump to 0xffff0 to reboot.  I didn't know back when I
wrote reboot.c, but this is supposedly more reliable since we're jumping to
code in ROM which hasn't been overwritten (kern/i386/pc/startup.S uses the
same trick for its own grub_reboot()).

See attached patch.

-- 
Robert Millan

  The DRM opt-in fallacy: "Your data belongs to us. We will decide when (and
  how) you may access your data; but nobody's threatening your freedom: we
  still allow you to remove your data and not access it at all."

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2009-07-07  Robert Millan  <rmh.grub@aybabtu.com>

	* conf/i386-coreboot.rmk (reboot_mod_SOURCES): Remove
	`kern/i386/reboot.c'.
	* kern/i386/qemu/startup.S: Include `"../realmode.S"'.
	(grub_reboot): New function.
	* kern/i386/realmode.S: Include `<grub/machine/machine.h>'.
	(prot_to_real): Only enable i8086 interrupts on i386-pc.
	* include/grub/i386/coreboot/init.h (grub_reboot): New function
	prototype.

Index: conf/i386-coreboot.rmk
===================================================================
--- conf/i386-coreboot.rmk	(revision 2398)
+++ conf/i386-coreboot.rmk	(working copy)
@@ -174,7 +174,7 @@ linux_mod_CFLAGS = $(COMMON_CFLAGS)
 linux_mod_LDFLAGS = $(COMMON_LDFLAGS)
 
 # For reboot.mod.
-reboot_mod_SOURCES = commands/reboot.c kern/i386/reboot.c
+reboot_mod_SOURCES = commands/reboot.c
 reboot_mod_CFLAGS = $(COMMON_CFLAGS)
 reboot_mod_LDFLAGS = $(COMMON_LDFLAGS)
 
Index: kern/i386/qemu/startup.S
===================================================================
--- kern/i386/qemu/startup.S	(revision 2398)
+++ kern/i386/qemu/startup.S	(working copy)
@@ -95,3 +95,11 @@ codestart:
 
 	/* This should never happen.  */
 	jmp	EXT_C(grub_stop)
+
+#include "../realmode.S"
+
+FUNCTION(grub_reboot)
+	call    prot_to_real
+	.code16
+	ljmp	$0xf000, $0xfff0
+	.code32
Index: kern/i386/realmode.S
===================================================================
--- kern/i386/realmode.S	(revision 2398)
+++ kern/i386/realmode.S	(working copy)
@@ -41,6 +41,8 @@
  *       with "ret $N" where N is ((the number of arguments) - 3) * 4.
  */
 
+#include <grub/machine/machine.h>
+
 /*
  *  This is the area for all of the special variables.
  */
@@ -215,8 +217,10 @@ realcseg:
 	movw	%ax, %gs
 	movw	%ax, %ss
 
+#ifdef GRUB_MACHINE_PCBIOS
 	/* restore interrupts */
 	sti
+#endif
 
 	/* return on new stack! */
 	DATA32	ret
Index: include/grub/i386/coreboot/init.h
===================================================================
--- include/grub/i386/coreboot/init.h	(revision 2398)
+++ include/grub/i386/coreboot/init.h	(working copy)
@@ -1,6 +1,6 @@
 /*
  *  GRUB  --  GRand Unified Bootloader
- *  Copyright (C) 2007  Free Software Foundation, Inc.
+ *  Copyright (C) 2007,2009  Free Software Foundation, Inc.
  *
  *  GRUB is free software: you can redistribute it and/or modify
  *  it under the terms of the GNU General Public License as published by
@@ -24,5 +24,6 @@
 
 void EXPORT_FUNC(grub_stop) (void) __attribute__ ((noreturn));
 void EXPORT_FUNC(grub_stop_floppy) (void);
+void EXPORT_FUNC (grub_reboot) (void) __attribute__ ((noreturn));
 
 #endif