linux-kernel - Re: [PATCH] intel_idle: PCI quirk to prevent Lenovo Ideapad s10-3 boot hang

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Date:	Sat, 16 Oct 2010 04:25:59 -0400 (EDT)
From:	Len Brown <lenb@...nel.org>
To:	Matthew Garrett <mjg59@...f.ucam.org>
Cc:	Linux Power Management List <linux-pm@...ts.osdl.org>,
	linux-pci@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] intel_idle: PCI quirk to prevent Lenovo Ideapad s10-3 boot
 hang

> > > > we check (and clear) that bit only if the acpi tables
> > > > tell us to do so.
> > > 
> > > Do the tables tell us to do so on this platform?
> > 
> > In this configuration, yes, otherwise acpi_idle
> > would have failed in exactly the same way.
> 
> So why is intel_idle not paying attention to what the platform is 
> requesting?

ACPI's BM_STS mechanism is obsolete, and is fundmentally
incompatible with a tickless OS.  The status bit is a NO-OP
on most modern chip-sets under normal conditions.
However, even when not a NO-OP, it is supposed to
be just an indicator and clearing it should have
no functional effect on the hardware except to
re-arm the hardware that looks for BM_STS.

Clearing BM_STS on the NM10 chipset at boot-time to
make the system boot has nothing to do with
"what the platform is requesting".
It is a workaround for a platform bug that is randomly
masked by how the behaviour of the legacy ACPI OS.

intel_idle it knows nothing about ACPI, and it never will.

thanks,
Len Brown, Intel Open Source Technology Center

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