linux-kernel - Re: [PATCH] drivers/cpufreq: Warn user when powernow-k8 tries to fall back to acpi-cpufreq and it is unavailable.

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Date:	Fri, 18 Jan 2013 19:06:59 +0000
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Borislav Petkov <bp@...en8.de>,
	"Gopalakrishnan, Aravind" <Aravind.Gopalakrishnan@....com>,
	"rjw@...k.pl" <rjw@...k.pl>, Andre Przywara <andre@...rep.de>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Andreas <linuxuser330250@....net>
Subject: Re: [PATCH] drivers/cpufreq: Warn user when powernow-k8 tries to
 fall back to acpi-cpufreq and it is unavailable.

On Fri, Jan 18, 2013 at 08:00:21PM +0100, Borislav Petkov wrote:

> ##################################################################################
> # x86 drivers.
> # Link order matters. K8 is preferred to ACPI because of firmware bugs in early
> # K8 systems.
> ...
> 
> Great. :(

The only case I can see this hitting would be if the platform is using 
system IO rather than fixed hardware functionality. Easiest thing to do 
there would be something like this:

diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
index 0d048f6..8b466d5 100644
--- a/drivers/cpufreq/acpi-cpufreq.c
+++ b/drivers/cpufreq/acpi-cpufreq.c
@@ -762,6 +762,11 @@ static int acpi_cpufreq_cpu_init(struct cpufreq_policy *policy)
 
 	switch (perf->control_register.space_id) {
 	case ACPI_ADR_SPACE_SYSTEM_IO:
+		if (boot_cpu_data.x86_vendor == X86_VENDOR_AMD) {
+			pr_debug("Old AMD systems must use native drivers\n");
+			result = -ENODEV;
+			goto err_unreg;
+		}
 		pr_debug("SYSTEM IO addr space\n");
 		data->cpu_feature = SYSTEM_IO_CAPABLE;
 		break;

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