Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <abc402b1-1253-fe94-94c4-afb1dfb9aebd@gmail.com>
Date:   Thu, 13 Oct 2022 04:19:03 +0900
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.11.0
Subject: Re: [PATCH v2] devfreq: governor: Add a private governor_data for
 governors in devfreq
Content-Language: en-US
From:   Chanwoo Choi <cwchoi00@gmail.com>
To:     Kant Fan <kant@allwinnertech.com>, myungjoo.ham@samsung.com,
        kyungmin.park@samsung.com, cw00.choi@samsung.com
Cc:     linux-pm@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20221010072202.78731-1-kant@allwinnertech.com>
 <00ed0b46-54db-330e-8ff8-146ff9a09491@gmail.com>
In-Reply-To: <00ed0b46-54db-330e-8ff8-146ff9a09491@gmail.com>
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 22. 10. 13. 04:00, Chanwoo Choi wrote:
> Hi,
> 
> I'm sorry for late reply. It looks good to me.
> Instead, this patch should contain the 'Fixes' information
> with the following commit because the changed code was merged
> on the patch[1]. Also, need to send it to stable mailing list.
> 
> [1] ce26c5bb9569d8b826f01b8620fc16d8da6821e9
> PM / devfreq: Add basic governors
> 
> Lastly, I think that need to change the patch title as following:
> - PM / devfreq: governor: Add a private governor_data for governor
> 
> 
> On 22. 10. 10. 16:22, 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.
>>
>> Acked-by: MyungJoo Ham <myungjoo.ham@samsung.com>
>>
>> Signed-off-by: Kant Fan <kant@allwinnertech.com>
>> ---
>>  drivers/devfreq/governor_userspace.c | 12 ++++++------
>>  include/linux/devfreq.h              |  7 ++++---
>>  2 files changed, 10 insertions(+), 9 deletions(-)
>>
>> 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..d265af3fb0a4 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 core pass to governors, governor should not change it.

In addition, the devfreq driver pass the 'data' from devfreq driver
to governor by using devfreq_add_device. I think that 'devfreq driver'
is more proper 

* @data:	devfreq driver pass to governors, governor should not change it.

And then, there are extra changes required.

diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
index 63347a5ae599..0c59b7978391 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

-- 
Best Regards,
Samsung Electronics
Chanwoo Choi