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

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Message-ID: <20090430095414.GA19462@srcf.ucam.org>
Date:	Thu, 30 Apr 2009 10:54:14 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Darrick J. Wong" <djwong@...ibm.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, Apr 30, 2009 at 09:25:56AM +0200, Ingo Molnar wrote:

> OTOH, if you rely on me figuring out which patch to revert and what 
> to do, it will take an indeterminate amount of time - together with 
> all the other items in my 'would be nice to hack on, given a bit of 
> free time' queue :)

Here's Darrick's patch:

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.

This second version restores the correct function call, which simplifies
the patch.  I apologize for the churn and the poor eyesight.

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 cafb410..85af717 100644
--- a/drivers/acpi/processor_perflib.c
+++ b/drivers/acpi/processor_perflib.c
@@ -348,7 +348,11 @@ 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

-- 
Matthew Garrett | mjg59@...f.ucam.org
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