RE: [PATCH v6 08/11] cpufreq: amd_pstate: add driver working mode status sysfs entry

[Yuan, Perry]

[AMD Official Use Only - General]

Hi Mario.

> -----Original Message-----
> From: Limonciello, Mario <Mario.Limonciello@xxxxxxx>
> Sent: Friday, December 2, 2022 11:57 PM
> To: Yuan, Perry <Perry.Yuan@xxxxxxx>; rafael.j.wysocki@xxxxxxxxx; Huang,
> Ray <Ray.Huang@xxxxxxx>; viresh.kumar@xxxxxxxxxx
> Cc: Sharma, Deepak <Deepak.Sharma@xxxxxxx>; Fontenot, Nathan
> <Nathan.Fontenot@xxxxxxx>; Deucher, Alexander
> <Alexander.Deucher@xxxxxxx>; Huang, Shimmer
> <Shimmer.Huang@xxxxxxx>; Du, Xiaojian <Xiaojian.Du@xxxxxxx>; Meng,
> Li (Jassmine) <Li.Meng@xxxxxxx>; Karny, Wyes <Wyes.Karny@xxxxxxx>;
> linux-pm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: Re: [PATCH v6 08/11] cpufreq: amd_pstate: add driver working
> mode status sysfs entry
> 
> On 12/2/2022 01:47, Perry Yuan wrote:
> > From: Perry Yuan <Perry.Yuan@xxxxxxx>
> >
> > While amd-pstate driver was loaded with specific driver mode, it will
> 
> The *driver* doesn't need to check which mode is enabled from the sysfs
> file, but userspace may want to check this.  I think you should reword this
> accordingly in the commit message.
> 
> > need to check which mode is enabled for the pstate driver,add this
> > sysfs entry to show the current status
> >
> > $ cat /sys/devices/system/cpu/amd-pstate/status
> > active
> >
> > Signed-off-by: Perry Yuan <Perry.Yuan@xxxxxxx>
> > ---
> >   drivers/cpufreq/amd-pstate.c | 44
> ++++++++++++++++++++++++++++++++++++
> >   1 file changed, 44 insertions(+)
> >
> > diff --git a/drivers/cpufreq/amd-pstate.c
> > b/drivers/cpufreq/amd-pstate.c index 6936df6e8642..7f748a579023 100644
> > --- a/drivers/cpufreq/amd-pstate.c
> > +++ b/drivers/cpufreq/amd-pstate.c
> > @@ -66,6 +66,8 @@ static bool cppc_active;
> >   static int cppc_load __initdata;
> >
> >   static struct cpufreq_driver *default_pstate_driver;
> > +static struct cpufreq_driver amd_pstate_epp_driver; static struct
> > +cpufreq_driver amd_pstate_driver;
> >   static struct amd_cpudata **all_cpu_data;
> >   static struct amd_pstate_params global_params;
> >
> > @@ -807,6 +809,46 @@ static ssize_t store_boost(struct kobject *a,
> >   	return count;
> >   }
> >
> > +static ssize_t amd_pstate_show_status(char *buf) {
> > +	if (!default_pstate_driver)
> > +		return sysfs_emit(buf, "off\n");
> > +
> > +	return sysfs_emit(buf, "%s\n", default_pstate_driver ==
> &amd_pstate_epp_driver ?
> > +					"active" : "passive");
> > +}
> > +
> > +static int amd_pstate_update_status(const char *buf, size_t size) {
> > +	/* FIXME! */
> > +	return -EOPNOTSUPP;
> > +}
> 
> Why not just fix this as part of the series?  It should be no different than
> unloading the driver and reloading it in the appropriate mode, right?

There is one kernel hang issue for the amd-pstate driver when unloading it before this. 
I have added one fix patch for this in V7, and added the driver mode switching code as well.
The driver mode can be switched now.

Perry.

> 
> Is this going to be a short term FIXME/TODO or a long term?  If it's long term,
> it might be better to just make the attribute ro and and have just the show
> callback.  Then when you're ready to make it rw you can add the store
> callback, change it from ro to rw and update documentation at that time.
> 

Fixed in V7. It is working well now. 

> > +
> > +static ssize_t show_status(struct kobject *kobj,
> > +			   struct kobj_attribute *attr, char *buf)
> > +{
> > +	ssize_t ret;
> > +
> > +	mutex_lock(&amd_pstate_driver_lock);
> > +	ret = amd_pstate_show_status(buf);
> > +	mutex_unlock(&amd_pstate_driver_lock);
> > +
> > +	return ret;
> > +}
> > +
> > +static ssize_t store_status(struct kobject *a, struct kobj_attribute *b,
> > +			    const char *buf, size_t count)
> > +{
> > +	char *p = memchr(buf, '\n', count);
> > +	int ret;
> > +
> > +	mutex_lock(&amd_pstate_driver_lock);
> > +	ret = amd_pstate_update_status(buf, p ? p - buf : count);
> > +	mutex_unlock(&amd_pstate_driver_lock);
> > +
> > +	return ret < 0 ? ret : count;
> > +}
> > +
> >   cpufreq_freq_attr_ro(amd_pstate_max_freq);
> >   cpufreq_freq_attr_ro(amd_pstate_lowest_nonlinear_freq);
> >
> > @@ -814,6 +856,7 @@ cpufreq_freq_attr_ro(amd_pstate_highest_perf);
> >   cpufreq_freq_attr_rw(energy_performance_preference);
> >   cpufreq_freq_attr_ro(energy_performance_available_preferences);
> >   define_one_global_rw(boost);
> > +define_one_global_rw(status);
> >
> >   static struct freq_attr *amd_pstate_attr[] = {
> >   	&amd_pstate_max_freq,
> > @@ -833,6 +876,7 @@ static struct freq_attr *amd_pstate_epp_attr[] = {
> >
> >   static struct attribute *pstate_global_attributes[] = {
> >   	&boost.attr,
> > +	&status.attr,
> 
> In the series I didn't see a matching Documentation update for the new
> sysfs file, can you please add one?

Added in V7.
Please help to take a look

> 
> >   	NULL
> >   };
> >