Re: [PATCH] PCI: Add pci shutdown ability

[Pavel Machek <pavel@ucw.cz>]

On Po 25-04-05 18:13:27, Dave Jones wrote:
> On Mon, Apr 25, 2005 at 02:58:31PM -0700, Andrew Morton wrote:
>  > Alan Stern <stern@rowland.harvard.edu> wrote:
>  > >
>  > > On Mon, 25 Apr 2005, Alexander Nyberg wrote:
>  > > 
>  > > > Not sure what you mean by "make kexec work nicer" but if it is because
>  > > > some devices don't work after a kexec I have some objections.
>  > > 
>  > > That was indeed the reason, at least in my case.  The newly-rebooted
>  > > kernel doesn't work too well when there are active devices, with no driver
>  > > loaded, doing DMA and issuing IRQs because they were never shut down.
>  > 
>  > I have vague memories of this being discussed at some length last year. 
>  > Nothing comprehensive came of it, except that perhaps the kdump code should
>  > spin with irqs off for a couple of seconds so the DMA and IRQs stop.
>  > 
>  > (Ongoing DMA is not a problem actually, because the kdump kernel won't be
>  > using that memory anyway)
> 
> Actually, some cpufreq drivers *should* do their speed transitions with
> all PCI mastering disabled. The lack of any infrastructure to quiesce drivers
> and prevent new DMA transactions from occuring whilst the transition occurs
> means that currently.. we don't.  So +1 for any driver model work that
> may lead to something we can use here.

Well, you can do "half suspend to ram; change your frequency; half
resume" today, and it should work, but I do not think you'll like the
speed.

In a ideal world, calling device_suspend(PMSG_FREEZE) gets you exactly
that, and we'll do our best to make it fast enough.

OTOH it *needs* to switch consoles to text one (because X may be
running DMA, right?); I do not think you'll like that one.
								Pavel
-- 
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