Date:   Tue, 25 Oct 2022 15:57:22 +0800
From:   Kant Fan <kant@...winnertech.com>
To:     Chanwoo Choi <cwchoi00@...il.com>, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, cw00.choi@...sung.com, khilman@...com,
        rjw@...ysocki.net, mturquette@...com
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] PM/devfreq: governor: Add a private governor_data for
 governor

On 10/22/2022 7:41 AM, Chanwoo Choi wrote:
> Hi,
> 
> Looks good to me. But, you need to send it to the stable mailing list
> too as I commented on previous mail.
> 
> Please add stable@...r.kernel.org to Cc.
> 

Hi Chanwoo,
Thanks for the notice. Please review this patch-v4 [1].

[1]
https://lore.kernel.org/all/20221025072109.64025-1-kant@allwinnertech.com/

-- 
Best Regards,
Kant Fan

> On 22. 10. 14. 18:43, Kant Fan wrote:
>> The member void *data in the structure devfreq can be overwrite
>> by governor_userspace. For example:
>> 1. The device driver assigned the devfreq governor to simple_ondemand
>> by the function devfreq_add_device() and init the devfreq member
>> void *data to a pointer of a static structure devfreq_simple_ondemand_data
>> by the function devfreq_add_device().
>> 2. The user changed the devfreq governor to userspace by the command
>> "echo userspace > /sys/class/devfreq/.../governor".
>> 3. The governor userspace alloced a dynamic memory for the struct
>> userspace_data and assigend the member void *data of devfreq to
>> this memory by the function userspace_init().
>> 4. The user changed the devfreq governor back to simple_ondemand
>> by the command "echo simple_ondemand > /sys/class/devfreq/.../governor".
>> 5. The governor userspace exited and assigned the member void *data
>> in the structure devfreq to NULL by the function userspace_exit().
>> 6. The governor simple_ondemand fetched the static information of
>> devfreq_simple_ondemand_data in the function
>> devfreq_simple_ondemand_func() but the member void *data of devfreq was
>> assigned to NULL by the function userspace_exit().
>> 7. The information of upthreshold and downdifferential is lost
>> and the governor simple_ondemand can't work correctly.
>>
>> The member void *data in the structure devfreq is designed for
>> a static pointer used in a governor and inited by the function
>> devfreq_add_device(). This patch add an element named governor_data
>> in the devfreq structure which can be used by a governor(E.g userspace)
>> who want to assign a private data to do some private things.
>>
>> Fixes: ce26c5bb9569 ("PM / devfreq: Add basic governors")
>>
>> Acked-by: MyungJoo Ham <myungjoo.ham@...sung.com>
>>
>> Signed-off-by: Kant Fan <kant@...winnertech.com>
>> ---
>>   drivers/devfreq/devfreq.c            |  6 ++----
>>   drivers/devfreq/governor_userspace.c | 12 ++++++------
>>   include/linux/devfreq.h              |  7 ++++---
>>   3 files changed, 12 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
>> index 63347a5ae599..8c5f6f7fca11 100644
>> --- a/drivers/devfreq/devfreq.c
>> +++ b/drivers/devfreq/devfreq.c
>> @@ -776,8 +776,7 @@ static void remove_sysfs_files(struct devfreq *devfreq,
>>    * @dev:	the device to add devfreq feature.
>>    * @profile:	device-specific profile to run devfreq.
>>    * @governor_name:	name of the policy to choose frequency.
>> - * @data:	private data for the governor. The devfreq framework does not
>> - *		touch this value.
>> + * @data:	devfreq driver pass to governors, governor should not change it.
>>    */
>>   struct devfreq *devfreq_add_device(struct device *dev,
>>   				   struct devfreq_dev_profile *profile,
>> @@ -1011,8 +1010,7 @@ static void devm_devfreq_dev_release(struct device *dev, void *res)
>>    * @dev:	the device to add devfreq feature.
>>    * @profile:	device-specific profile to run devfreq.
>>    * @governor_name:	name of the policy to choose frequency.
>> - * @data:	private data for the governor. The devfreq framework does not
>> - *		touch this value.
>> + * @data:	 devfreq driver pass to governors, governor should not change it.
>>    *
>>    * This function manages automatically the memory of devfreq device using device
>>    * resource management and simplify the free operation for memory of devfreq
>> diff --git a/drivers/devfreq/governor_userspace.c b/drivers/devfreq/governor_userspace.c
>> index ab9db7adb3ad..d69672ccacc4 100644
>> --- a/drivers/devfreq/governor_userspace.c
>> +++ b/drivers/devfreq/governor_userspace.c
>> @@ -21,7 +21,7 @@ struct userspace_data {
>>   
>>   static int devfreq_userspace_func(struct devfreq *df, unsigned long *freq)
>>   {
>> -	struct userspace_data *data = df->data;
>> +	struct userspace_data *data = df->governor_data;
>>   
>>   	if (data->valid)
>>   		*freq = data->user_frequency;
>> @@ -40,7 +40,7 @@ static ssize_t set_freq_store(struct device *dev, struct device_attribute *attr,
>>   	int err = 0;
>>   
>>   	mutex_lock(&devfreq->lock);
>> -	data = devfreq->data;
>> +	data = devfreq->governor_data;
>>   
>>   	sscanf(buf, "%lu", &wanted);
>>   	data->user_frequency = wanted;
>> @@ -60,7 +60,7 @@ static ssize_t set_freq_show(struct device *dev,
>>   	int err = 0;
>>   
>>   	mutex_lock(&devfreq->lock);
>> -	data = devfreq->data;
>> +	data = devfreq->governor_data;
>>   
>>   	if (data->valid)
>>   		err = sprintf(buf, "%lu\n", data->user_frequency);
>> @@ -91,7 +91,7 @@ static int userspace_init(struct devfreq *devfreq)
>>   		goto out;
>>   	}
>>   	data->valid = false;
>> -	devfreq->data = data;
>> +	devfreq->governor_data = data;
>>   
>>   	err = sysfs_create_group(&devfreq->dev.kobj, &dev_attr_group);
>>   out:
>> @@ -107,8 +107,8 @@ static void userspace_exit(struct devfreq *devfreq)
>>   	if (devfreq->dev.kobj.sd)
>>   		sysfs_remove_group(&devfreq->dev.kobj, &dev_attr_group);
>>   
>> -	kfree(devfreq->data);
>> -	devfreq->data = NULL;
>> +	kfree(devfreq->governor_data);
>> +	devfreq->governor_data = NULL;
>>   }
>>   
>>   static int devfreq_userspace_handler(struct devfreq *devfreq,
>> diff --git a/include/linux/devfreq.h b/include/linux/devfreq.h
>> index 34aab4dd336c..4dc7cda4fd46 100644
>> --- a/include/linux/devfreq.h
>> +++ b/include/linux/devfreq.h
>> @@ -152,8 +152,8 @@ struct devfreq_stats {
>>    * @max_state:		count of entry present in the frequency table.
>>    * @previous_freq:	previously configured frequency value.
>>    * @last_status:	devfreq user device info, performance statistics
>> - * @data:	Private data of the governor. The devfreq framework does not
>> - *		touch this.
>> + * @data:	devfreq driver pass to governors, governor should not change it.
>> + * @governor_data:	private data for governors, devfreq core doesn't touch it.
>>    * @user_min_freq_req:	PM QoS minimum frequency request from user (via sysfs)
>>    * @user_max_freq_req:	PM QoS maximum frequency request from user (via sysfs)
>>    * @scaling_min_freq:	Limit minimum frequency requested by OPP interface
>> @@ -193,7 +193,8 @@ struct devfreq {
>>   	unsigned long previous_freq;
>>   	struct devfreq_dev_status last_status;
>>   
>> -	void *data; /* private data for governors */
>> +	void *data;
>> +	void *governor_data;
>>   
>>   	struct dev_pm_qos_request user_min_freq_req;
>>   	struct dev_pm_qos_request user_max_freq_req;
> 

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