Re: [Qemu-devel] [PATCH 4/3] wakeup: only reset the CPU

[Laszlo Ersek]

On 03/05/13 17:59, David Woodhouse wrote:> On Tue, 2013-03-05 at 17:03 +0100, 
Paolo Bonzini wrote:
>> Resuming from suspend-to-RAM should not reset all devices.  Only the
>> CPU should get a reset signal.
>
> Hm... on reflection, I don't actually know if this is true.
>
> Perhaps we *should* reset all devices. After all, in a real machine
> they'll all have been turned off and the RAM will have been in
> self-refresh. Surely they have to be reset?
>
> So maybe we should *let* the i440FX PAM registers get reset to point to
> ROM. And fix the firmware to *cope* with that, check to see if the
> shadow RAM already holds an image of a started-up firmware with the
> correct checksum, and jump back to it.
>
> That is: perhaps it's a *SeaBIOS* bug that suspend/resume doesn't work
> if the PAM configuration is reset?

I think it is indeed a problem with SeaBIOS. (git.seabios.org
(80.81.252.135) seems to be down ATM, so I can only check at f465e1ec.)
Open romlayout.S:

   622  reset_vector:
   623          ljmpw $SEG_BIOS, $entry_post

   537  entry_post:
   538          cmpl $0, %cs:HaveRunPost                // Check for 
resume/reboot
   539          jnz entry_resume
   540          ENTRY_INTO32 _cfunc32flat_handle_post   // Normal entry point

   239  entry_resume:
...
   248          // Call handler.
   249          jmp handle_resume

handle_resume() [src/resume.c]
  inb_cmos(CMOS_RESET_CODE)

It checks the CMOS only after looking at HaveRunPost. The value of
HaveRunPost depends on the PAM settings. It's always 0 in ROM, in which
case we continue at handle_post() [src/post.c].

Laszlo