Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))
From: Nigel Cunningham (ncunningham_at_linuxmail.org)
Date: 02/04/05
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- In reply to: Carl-Daniel Hailfinger: "[RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
- Next in thread: Jon Smirl: "Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
- Reply: Jon Smirl: "Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
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To: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2005@gmx.net> Date: Fri, 04 Feb 2005 13:51:55 +1100
Hi.
On Fri, 2005-02-04 at 13:35, Carl-Daniel Hailfinger wrote:
> 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.
Yuckkkkk!
> 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
That's no biggie.
> - vesafb has to refrain from touching video until after POST
Which is why I think we should do the post asap (as you have). What is
counted as an essential thread?
> - the vesaposter thread has to be the first unfrozen and
> scheduled and completed thread. Only after that we can resume
> vesafb and other threads
All other threads will be frozen, and we don't have scheduler hooks that
will hang up our new kiddie, so we should be right there.
> - the locking will be tricky
But also simplified by the fact that everything else is frozen.
> Advantages:
> - the problems all seem to be solvable easily
> - security and stability are similar to the current userspace code
> - we can use vesafb on such machines
> - the kernel code won't be much more than two dozen lines
> - the userspace POSTing code can be upgraded without the need
> for kernel updates (no policy in the kernel)
>
> What do you think?
Show us some code :>
Nigel
-- Nigel Cunningham Software Engineer, Canberra, Australia http://www.cyclades.com Ph: +61 (2) 6292 8028 Mob: +61 (417) 100 574 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
- Previous message: Bartlomiej Zolnierkiewicz: "[patch 9/9] convert device drivers to driver-model"
- In reply to: Carl-Daniel Hailfinger: "[RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
- Next in thread: Jon Smirl: "Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
- Reply: Jon Smirl: "Re: [RFC] Reliable video POSTing on resume (was: Re: [ACPI] Samsung P35, S3, black screen (radeon))"
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