Re: [PATCH v2 3/6] devfreq: Factor out devfreq_set_governor()

[Yaxiong Tian <tianyaxiong@kylinos.cn>]

在 2026/5/13 17:38, Jie Zhan 写道:
> Factor out common governor setting logic into devfreq_set_governor() so as
> to consolidate the code in governor_store() and devfreq_add_device().
>
> The caller is expected to hold 'devfreq_list_lock', enforced via
> lockdep_assert_held().  This is required because devfreq_add_device() must
> hold the lock from setting governor until the device is added to
> 'devfreq_list', so that a concurrent devfreq_remove_governor() cannot free
> the governor in between.
>
> Signed-off-by: Jie Zhan <zhanjie9@hisilicon.com>

I'm a bit unclear about the purpose of this commit, or the problem it 
solves. Can you explain it more clearly?


> ---
>   drivers/devfreq/devfreq.c | 117 ++++++++++++++++++--------------------
>   1 file changed, 56 insertions(+), 61 deletions(-)
>
> diff --git a/drivers/devfreq/devfreq.c b/drivers/devfreq/devfreq.c
> index 53c40d795a13..9e3e6a7348f8 100644
> --- a/drivers/devfreq/devfreq.c
> +++ b/drivers/devfreq/devfreq.c
> @@ -318,6 +318,59 @@ static struct devfreq_governor *try_then_request_governor(const char *name)
>   	return governor;
>   }
>   
> +static int devfreq_set_governor(struct devfreq *df,
> +				const struct devfreq_governor *new_gov)
> +{
> +	const struct devfreq_governor *old_gov;
> +	struct device *dev;
> +	int ret;
> +
> +	lockdep_assert_held(&devfreq_list_lock);
> +
> +	old_gov = df->governor;
> +	dev = &df->dev;
> +
> +	if (old_gov) {
> +		if (old_gov == new_gov)
> +			return 0;
> +
> +		if (IS_SUPPORTED_FLAG(old_gov->flags, IMMUTABLE) ||
> +		    IS_SUPPORTED_FLAG(new_gov->flags, IMMUTABLE))
> +			return -EINVAL;
> +
> +		/* Stop the current governor */
> +		ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
> +		if (ret) {
> +			dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
> +				 __func__, df->governor->name, ret);
> +			return ret;
> +		}
> +	}
> +
> +	/* Start the new governor */
> +	df->governor = new_gov;
> +	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> +	if (ret) {
> +		dev_warn(dev, "%s: Governor %s not started(%d)\n",
> +			 __func__, df->governor->name, ret);
> +
> +		/* Restore previous governor */
> +		df->governor = old_gov;
> +		if (!df->governor)
> +			return ret;
> +
> +		ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> +		if (ret) {
> +			dev_err(dev, "%s: restore Governor %s failed (%d)\n",
> +				__func__, df->governor->name, ret);
> +			df->governor = NULL;
> +			return ret;
> +		}
> +	}
> +
> +	return sysfs_update_group(&df->dev.kobj, &gov_attr_group);
> +}
> +
>   static int devfreq_notify_transition(struct devfreq *devfreq,
>   		struct devfreq_freqs *freqs, unsigned int state)
>   {
> @@ -942,9 +995,7 @@ struct devfreq *devfreq_add_device(struct device *dev,
>   		goto err_init;
>   	}
>   
> -	devfreq->governor = governor;
> -	err = devfreq->governor->event_handler(devfreq, DEVFREQ_GOV_START,
> -						NULL);
> +	err = devfreq_set_governor(devfreq, governor);
>   	if (err) {
>   		dev_err_probe(dev, err,
>   			"%s: Unable to start governor for the device\n",
> @@ -952,10 +1003,6 @@ struct devfreq *devfreq_add_device(struct device *dev,
>   		goto err_init;
>   	}
>   
> -	err = sysfs_update_group(&devfreq->dev.kobj, &gov_attr_group);
> -	if (err)
> -		goto err_init;
> -
>   	list_add(&devfreq->node, &devfreq_list);
>   
>   	mutex_unlock(&devfreq_list_lock);
> @@ -1380,7 +1427,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>   	struct devfreq *df = to_devfreq(dev);
>   	int ret;
>   	char str_governor[DEVFREQ_NAME_LEN + 1];
> -	const struct devfreq_governor *governor, *prev_governor;
> +	const struct devfreq_governor *governor;
>   
>   	ret = sscanf(buf, "%" __stringify(DEVFREQ_NAME_LEN) "s", str_governor);
>   	if (ret != 1)
> @@ -1391,59 +1438,7 @@ static ssize_t governor_store(struct device *dev, struct device_attribute *attr,
>   	if (IS_ERR(governor))
>   		return PTR_ERR(governor);
>   
> -	if (!df->governor)
> -		goto start_new_governor;
> -
> -	if (df->governor == governor)
> -		return count;
> -
> -	if (IS_SUPPORTED_FLAG(df->governor->flags, IMMUTABLE) ||
> -	    IS_SUPPORTED_FLAG(governor->flags, IMMUTABLE))
> -		return -EINVAL;
> -
> -	/*
> -	 * Stop the current governor and remove the specific sysfs files
> -	 * which depend on current governor.
> -	 */
> -	ret = df->governor->event_handler(df, DEVFREQ_GOV_STOP, NULL);
> -	if (ret) {
> -		dev_warn(dev, "%s: Governor %s not stopped(%d)\n",
> -			 __func__, df->governor->name, ret);
> -		return ret;
> -	}
> -
> -start_new_governor:
> -	/*
> -	 * Start the new governor and create the specific sysfs files
> -	 * which depend on the new governor.
> -	 */
> -	prev_governor = df->governor;
> -	df->governor = governor;
> -	ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> -	if (ret) {
> -		dev_warn(dev, "%s: Governor %s not started(%d)\n",
> -			 __func__, df->governor->name, ret);
> -
> -		/* Restore previous governor */
> -		df->governor = prev_governor;
> -		if (!df->governor)
> -			return ret;
> -
> -		ret = df->governor->event_handler(df, DEVFREQ_GOV_START, NULL);
> -		if (ret) {
> -			dev_err(dev,
> -				"%s: reverting to Governor %s failed (%d)\n",
> -				__func__, prev_governor->name, ret);
> -			df->governor = NULL;
> -			return ret;
> -		}
> -	}
> -
> -	/*
> -	 * Create the sysfs files for the new governor. But if failed to start
> -	 * the new governor, restore the sysfs files of previous governor.
> -	 */
> -	ret = sysfs_update_group(&df->dev.kobj, &gov_attr_group);
> +	ret = devfreq_set_governor(df, governor);
>   	if (ret)
>   		return ret;
>