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Message-ID: <YAXQCK7dmHrSq29b@kroah.com>
Date: Mon, 18 Jan 2021 19:14:32 +0100
From: Greg KH <greg@...ah.com>
To: Lukasz Luba <lukasz.luba@....com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
cw00.choi@...sung.com, myungjoo.ham@...sung.com,
kyungmin.park@...sung.com
Subject: Re: [PATCH] PM / devfreq: Add sysfs attributes to simple_ondemand
governor
On Mon, Jan 18, 2021 at 05:56:06PM +0000, Lukasz Luba wrote:
>
>
> On 1/18/21 5:17 PM, Greg KH wrote:
> > On Fri, Jan 15, 2021 at 05:05:30PM +0000, Lukasz Luba wrote:
> > > The simple_ondemand devfreq governor is used by quite a few devices, like
> > > GPUs, DSPs, memory controllers, etc. It implements algorithm which tries
> > > to predict the device frequency based on past statistics. There are two
> > > tunables for the algorithm: 'upthreshold' and 'downdifferential'. These
> > > tunables change the behavior of the decision, e.g. how fast to increase
> > > the frequency or how rapidly limit the frequency. These values might be
> > > different based on the application which is currently running, e.g.
> > > different behavior is needed for a game than for web browsing or clean
> > > desktop. The patch exports these two tunables so they can be adjusted
> > > based on current need. There is also a check with the allowed ranges
> > > to make sure the values are correct and safe.
> > >
> > > Signed-off-by: Lukasz Luba <lukasz.luba@....com>
> > > ---
> > > drivers/devfreq/governor_simpleondemand.c | 135 ++++++++++++++++++++++
> > > 1 file changed, 135 insertions(+)
> > >
> > > diff --git a/drivers/devfreq/governor_simpleondemand.c b/drivers/devfreq/governor_simpleondemand.c
> > > index d57b82a2b570..4b3c182e0a49 100644
> > > --- a/drivers/devfreq/governor_simpleondemand.c
> > > +++ b/drivers/devfreq/governor_simpleondemand.c
> > > @@ -15,6 +15,7 @@
> > > /* Default constants for DevFreq-Simple-Ondemand (DFSO) */
> > > #define DFSO_UPTHRESHOLD (90)
> > > #define DFSO_DOWNDIFFERENCTIAL (5)
> > > +#define DFSO_MAX_VALUE (100)
> > > static int devfreq_simple_ondemand_func(struct devfreq *df,
> > > unsigned long *freq)
> > > {
> > > @@ -84,15 +85,149 @@ static int devfreq_simple_ondemand_func(struct devfreq *df,
> > > return 0;
> > > }
> > > +static ssize_t upthreshold_show(struct device *dev,
> > > + struct device_attribute *attr, char *buf)
> > > +{
> > > + struct devfreq_simple_ondemand_data *data;
> > > + struct devfreq *df = to_devfreq(dev);
> > > +
> > > + if (!df->data)
> > > + return -EINVAL;
> > > +
> > > + data = df->data;
> > > +
> > > + return sprintf(buf, "%d\n", data->upthreshold);
> >
> > sysfs_emit()?
> >
> > Also, you forgot the Documentation/ABI/ updates for new sysfs files :(
>
> True, I will remember next time.
>
> >
> >
> > > +}
> > > +
> > > +static ssize_t upthreshold_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t count)
> > > +{
> > > + struct devfreq_simple_ondemand_data *data;
> > > + struct devfreq *df = to_devfreq(dev);
> > > + unsigned int value;
> > > + int ret;
> > > +
> > > + if (!df->data)
> > > + return -EINVAL;
> > > +
> > > + data = df->data;
> > > +
> > > + ret = kstrtouint(buf, 10, &value);
> > > + if (ret < 0)
> > > + return -EINVAL;
> > > +
> > > + mutex_lock(&df->lock);
> > > +
> > > + if (value > DFSO_MAX_VALUE || value <= data->downdifferential) {
> > > + mutex_unlock(&df->lock);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + data->upthreshold = value;
> > > + mutex_unlock(&df->lock);
> > > +
> > > + return count;
> > > +}
> > > +static DEVICE_ATTR_RW(upthreshold);
> > > +
> > > +static ssize_t downdifferential_show(struct device *dev,
> > > + struct device_attribute *attr, char *buf)
> > > +{
> > > + struct devfreq_simple_ondemand_data *data;
> > > + struct devfreq *df = to_devfreq(dev);
> > > +
> > > + if (!df->data)
> > > + return -EINVAL;
> > > +
> > > + data = df->data;
> > > +
> > > + return sprintf(buf, "%d\n", data->downdifferential);
> > > +}
> > > +
> > > +static ssize_t downdifferential_store(struct device *dev,
> > > + struct device_attribute *attr,
> > > + const char *buf, size_t count)
> > > +{
> > > + struct devfreq_simple_ondemand_data *data;
> > > + struct devfreq *df = to_devfreq(dev);
> > > + unsigned int value;
> > > + int ret;
> > > +
> > > + if (!df->data)
> > > + return -EINVAL;
> > > +
> > > + data = df->data;
> > > +
> > > + ret = kstrtouint(buf, 10, &value);
> > > + if (ret < 0)
> > > + return -EINVAL;
> > > +
> > > + mutex_lock(&df->lock);
> > > +
> > > + if (value > DFSO_MAX_VALUE || value >= data->upthreshold) {
> > > + mutex_unlock(&df->lock);
> > > + return -EINVAL;
> > > + }
> > > +
> > > + data->downdifferential = value;
> > > + mutex_unlock(&df->lock);
> > > +
> > > + return count;
> > > +}
> > > +static DEVICE_ATTR_RW(downdifferential);
> > > +
> > > +static void devfreq_simple_ondemand_sysfs_setup(struct devfreq *df)
> > > +{
> > > + struct devfreq_simple_ondemand_data *data;
> > > + int ret;
> > > +
> > > + if (!df->data) {
> > > + /* The memory will be freed automatically */
> > > + df->data = devm_kzalloc(&df->dev,
> > > + sizeof(struct devfreq_simple_ondemand_data),
> > > + GFP_KERNEL);
> > > + if (!df->data) {
> > > + dev_warn(&df->dev, "Unable to allocate memory");
> > > + return;
> > > + }
> > > + }
> > > +
> > > + data = df->data;
> > > +
> > > + /* After new allocation setup default values, since they are used */
> > > + if (!data->upthreshold)
> > > + data->upthreshold = DFSO_UPTHRESHOLD;
> > > +
> > > + if (!data->downdifferential)
> > > + data->downdifferential = DFSO_DOWNDIFFERENCTIAL;
> > > +
> > > + ret = sysfs_create_file(&df->dev.kobj, &dev_attr_upthreshold.attr);
> > > + if (ret < 0)
> > > + dev_warn(&df->dev, "Unable to create 'upthreshold' attr\n");
> > > +
> > > + ret = sysfs_create_file(&df->dev.kobj, &dev_attr_downdifferential.attr);
> > > + if (ret < 0)
> > > + dev_warn(&df->dev, "Unable to create 'downdifferential' attr\n");
> >
> > You just raced with userspace and lost :(
> >
> > Please use the default sysfs groups so that it all works properly.
> >
> > Huge hint, when calling sysfs_* from a driver, that usually means you
> > are doing something wrong.
>
> I should have used kobject_init_and_add() and the default devfreq
> sysfs group as a parent.
No, never use "raw" kobjects in the sys/devices/ tree, that is a sure
way to ensure that userspace will never be notified or see your
attributes.
thanks,
greg k-h
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