Re: [PATCH 6/8] acpi-cpufreq: Add compatibility for legacy AMD cpb sysfs knob

From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Andre Przywara <andre.przywara@amd.com>
Cc: cpufreq@vger.kernel.org, Matthew Garrett <mjg@redhat.com>,
	Andreas Herrmann <andreas.herrmann3@amd.com>,
	Thomas Renninger <trenn@suse.de>,
	linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 6/8] acpi-cpufreq: Add compatibility for legacy AMD cpb sysfs knob
Date: Sun, 5 Aug 2012 23:29:36 +0200	[thread overview]
Message-ID: <201208052329.36556.rjw@sisk.pl> (raw)
In-Reply-To: <1343305724-2809-7-git-send-email-andre.przywara@amd.com>

On Thursday, July 26, 2012, Andre Przywara wrote:
> The powernow-k8 driver supported a sysfs knob called "cpb", which was
> instantiated per CPU, but actually acted globally for the whole
> system. To keep some compatibility with this feature, we re-introduce
> this behavior here, but:
> a) only enable it on AMD CPUs and
> b) protect it with a Kconfig switch
> 
> I'd like to consider this feature obsolete. Lets keep it around for
> some kernel versions and then phase it out.

You're not keeing it, but moving it to a different driver. :-)

Why don't we ask the users who really really want it to use powernow-k8
instead?

Rafael

> Signed-off-by: Andre Przywara <andre.przywara@amd.com>
> ---
>  drivers/cpufreq/Kconfig.x86    |   12 ++++++++++
>  drivers/cpufreq/acpi-cpufreq.c |   46 ++++++++++++++++++++++++++++++++++++++-
>  2 files changed, 56 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/cpufreq/Kconfig.x86 b/drivers/cpufreq/Kconfig.x86
> index 78ff7ee..d2f2320 100644
> --- a/drivers/cpufreq/Kconfig.x86
> +++ b/drivers/cpufreq/Kconfig.x86
> @@ -32,6 +32,18 @@ config X86_ACPI_CPUFREQ
>  
>  	  If in doubt, say N.
>  
> +config X86_ACPI_CPUFREQ_CPB
> +	default y
> +	bool "Legacy cpb sysfs knob support for AMD CPUs"
> +	depends on X86_ACPI_CPUFREQ && CPU_SUP_AMD
> +	help
> +	  The powernow-k8 driver used to provide a sysfs knob called "cpb"
> +	  to disable the Core Performance Boosting feature of AMD CPUs. This
> +	  file has now been superseeded by the more generic "boost" entry.
> +
> +	  By enabling this option the acpi_cpufreq driver provides the old
> +	  entry in addition to the new boost ones, for compatibility reasons.
> +
>  config ELAN_CPUFREQ
>  	tristate "AMD Elan SC400 and SC410"
>  	select CPU_FREQ_TABLE
> diff --git a/drivers/cpufreq/acpi-cpufreq.c b/drivers/cpufreq/acpi-cpufreq.c
> index ca41aaa..1ba4cac 100644
> --- a/drivers/cpufreq/acpi-cpufreq.c
> +++ b/drivers/cpufreq/acpi-cpufreq.c
> @@ -131,8 +131,7 @@ static void boost_set_msrs(bool enable, const struct cpumask *cpumask)
>  	wrmsr_on_cpus(cpumask, msr_addr, msrs);
>  }
>  
> -static ssize_t store_global_boost(struct kobject *kobj, struct attribute *attr,
> -				  const char *buf, size_t count)
> +static ssize_t _store_boost(const char *buf, size_t count)
>  {
>  	int ret;
>  	unsigned long val = 0;
> @@ -159,6 +158,12 @@ static ssize_t store_global_boost(struct kobject *kobj, struct attribute *attr,
>  	return count;
>  }
>  
> +static ssize_t store_global_boost(struct kobject *kobj, struct attribute *attr,
> +				  const char *buf, size_t count)
> +{
> +	return _store_boost(buf, count);
> +}
> +
>  static ssize_t show_global_boost(struct kobject *kobj,
>  				 struct attribute *attr, char *buf)
>  {
> @@ -169,6 +174,21 @@ static struct global_attr global_boost = __ATTR(boost, 0644,
>  						show_global_boost,
>  						store_global_boost);
>  
> +#ifdef CONFIG_X86_ACPI_CPUFREQ_CPB
> +static ssize_t store_cpb(struct cpufreq_policy *policy, const char *buf,
> +			 size_t count)
> +{
> +	return _store_boost(buf, count);
> +}
> +
> +static ssize_t show_cpb(struct cpufreq_policy *policy, char *buf)
> +{
> +	return sprintf(buf, "%u\n", boost_enabled);
> +}
> +
> +static struct freq_attr cpb = __ATTR(cpb, 0644, show_cpb, store_cpb);
> +#endif
> +
>  static int check_est_cpu(unsigned int cpuid)
>  {
>  	struct cpuinfo_x86 *cpu = &cpu_data(cpuid);
> @@ -887,6 +907,7 @@ static int acpi_cpufreq_resume(struct cpufreq_policy *policy)
>  
>  static struct freq_attr *acpi_cpufreq_attr[] = {
>  	&cpufreq_freq_attr_scaling_available_freqs,
> +	NULL,	/* this is a placeholder for cpb, do not remove */
>  	NULL,
>  };
>  
> @@ -958,6 +979,27 @@ static int __init acpi_cpufreq_init(void)
>  	if (ret)
>  		return ret;
>  
> +#ifdef CONFIG_X86_ACPI_CPUFREQ_CPB
> +	/* this is a sysfs file with a strange name and an even stranger
> +	 * semantic - per CPU instantiation, but system global effect.
> +	 * Lets enable it only on AMD CPUs for compatibility reasons and
> +	 * only if configured. This is considered legacy code, which
> +	 * will probably be removed at some point in the future.
> +	 */
> +	if (check_amd_hwpstate_cpu(0)) {
> +		struct freq_attr **iter;
> +
> +		pr_debug("adding sysfs entry for cpb\n");
> +
> +		for (iter = acpi_cpufreq_attr; *iter != NULL; iter++)
> +			;
> +
> +		/* make sure there is a terminator behind it */
> +		if (iter[1] == NULL)
> +			*iter = &cpb;
> +	}
> +#endif
> +
>  	ret = cpufreq_register_driver(&acpi_cpufreq_driver);
>  	if (ret)
>  		free_acpi_perf_data();
> 