linux-kernel - Re: [PATCH v2] acpi: Fix regression where _PPC is not read at boot even when ignore

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Date:	Thu, 18 Feb 2010 10:28:20 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Len Brown <lenb@...nel.org>
Cc:	Matthew Garrett <mjg@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	davej@...hat.com, Thomas Renninger <trenn@...e.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	cpufreq@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2] acpi: Fix regression where _PPC is not read at boot
	even when ignore_ppc=0

On Thu, Feb 18, 2010 at 04:02:39AM -0500, Len Brown wrote:
> > On Tue, Feb 16, 2010 at 10:07:07PM +0000, Matthew Garrett wrote:
> > > Did this ever get picked up?
> > 
> > Nope.  I vaguely recall asking a few times if there were any objections left,
> > but there weren't any, and I think Len or someone said it looked good back at
> > LPC last summer.  Does not appear in 2.6.33-rc8 though.
> 
> does it have a bugzilla entry? (as regressions tend to, thanks to rafael)
> I don't see this in my mailbox anymore.

Nope, no bugzilla entry.  Do I need to create one now?  A patch resend follows.

--D

---
Earlier, Ingo Molnar posted a patch to make it so that the kernel would avoid
reading _PPC on his broken T60.  Unfortunately, it seems that with Thomas
Renninger's patch last July to eliminate _PPC evaluations when the processor
driver loads, the kernel never actually reads _PPC at all!  This is problematic
if you happen to boot your non-T60 computer in a state where the BIOS _wants_
_PPC to be something other than zero.

So, put the _PPC evaluation back into acpi_processor_get_performance_info if
ignore_ppc isn't 1.

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---

 drivers/acpi/processor_perflib.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)


diff --git a/drivers/acpi/processor_perflib.c b/drivers/acpi/processor_perflib.c
index 2cabadc..a959f6a 100644
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -413,7 +413,11 @@ static int acpi_processor_get_performance_info(struct acpi_processor *pr)
 	if (result)
 		goto update_bios;
 
-	return 0;
+	/* We need to call _PPC once when cpufreq starts */
+	if (ignore_ppc != 1)
+		result = acpi_processor_get_platform_limit(pr);
+
+	return result;
 
 	/*
 	 * Having _PPC but missing frequencies (_PSS, _PCT) is a very good hint that
--
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