linux-kernel - Re: 2.6.31-rc2+: Interrupts enabled after cpufreq

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Message-ID: <20090710234646.GA11669@redhat.com>
Date:	Fri, 10 Jul 2009 19:46:47 -0400
From:	Dave Jones <davej@...hat.com>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Marcin Slusarz <marcin.slusarz@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux PM List <linux-pm@...ts.linux-foundation.org>,
	cpufreq@...r.kernel.org
Subject: Re: 2.6.31-rc2+: Interrupts enabled after cpufreq_suspend

On Sat, Jul 11, 2009 at 08:23:37AM +1000, Ben Herrenschmidt wrote:
 > On Fri, 2009-07-10 at 15:25 -0400, Dave Jones wrote:
 > 
 > > The answer seems to be in 42d4dc3f4e1ec1396371aac89d0dccfdd977191b
 > > which introduced all this code to work around some failure that only happens
 > > on PPC...
 > > 
 > >     [PATCH] Add suspend method to cpufreq core
 > >     
 > >     In order to properly fix some issues with cpufreq vs. sleep on
 > >     PowerBooks, I had to add a suspend callback to the pmac_cpufreq driver.
 > >     I must force a switch to full speed before sleep and I switch back to
 > >     previous speed on resume.
 > > 
 > > 
 > > Ben, is there something better we can do here ?
 > > 
 > > I really don't want to add an #ifdef __powerpc__ to core code if we can help it.
 > > I'd rather we didn't call into driver guts at all from the suspend path.
 > 
 > Wait a minute ... having a suspend/resume method in cpufreq is one
 > thing, having it muck around with SMP is another :-) The ppc code
 > doesn't do that.
 > 
 > There's nothing fundamentally "fail" in requiring a switch to a given
 > frequency before suspend. I don't know what kind of major FAIL the K8
 > code is doing here though :-)

The fail part comes from the fact that interrupts get reenabled.
And that's something that can easily happen out of our control if
we call into acpi_cpufreq's ->get method for example, so powernow-k8 isn't
the sole reason.

 > I'm happy instead of #ifdef's however to push the logic into the ppc
 > driver, or use a flag that the ppc driver sets to enable that logic.

Cool.

	Dave

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