Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))

[Pavel Machek <pavel@ucw.cz>]

Hi!

> > I'd love to see it too. Pavel, even if you don't want to merge it for a
> > while, we can always incorporate it in the Suspend2 patches so it gets
> > some testing. I know I'd try it on my i830 based Omnibook.
> 
> Can we use call_usermodehelper at this early resume stage (before any
> video access)? Calling vm86 directly is probably not going to fly
> because we want to be shielded from any misbehaviour in the bios code
> and it may be necessary to kill the process running the bios code.
> 
> Cases in point: My bios will cause the POSTing application to segfault.
> Others have reported the POSTing application just hangs, but the
> important things are done before the hang, so killing it after maybe
> 5 seconds would be ok.
> 
> Rough outline how to do that without adding tons of code:
> We need a call_usermodehelper_from_ram_with_timeout for that.
> 
> Kernel:                          Userspace:
> User wants to enter S3
> init_mutex_locked(s3_sem)
> call_usermodehelper("vesaposter")
>                                  vesaposter calls LRMI_init
>                                  vesaposter mlocks all its memory
>                                  vesaposter calls into kernel
>                                           and down(s3_sem)
> suspend vesafb
> 
> User has triggered resume
> run wakeup.S
> thaw essential threads
> set a timer of 5 seconds
> up(s3_sem)
> thaw and schedule vesaposter
> wait for timer or vesaposter termination
>                                  vesaposter returns from kernel
>                                  vesaposter posts video card
>                                  vesaposter terminates
> resume vesafb
> continue resume
> 
> Problems with that approach:
> - vesaposter has to be locked in memory to avoid disk accesses
> - vesafb has to refrain from touching video until after POST
> - the vesaposter thread has to be the first unfrozen and
>   scheduled and completed thread. Only after that we can resume
>   vesafb and other threads
> - the locking will be tricky

- it is ugly

What about simply blocking all video accesses before disk (etc) is
resumed, so that "normal" (not locked in memory) application can be
used?
								Pavel
-- 
People were complaining that M$ turns users into beta-testers...
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