Re: [PATCH v3 2/6] thermal: Add generic cpufreq cooling implementation

Andrew Morton
2012-05-08T20:16:32Z

On Tue, 8 May 2012 21:48:14 +0530
Amit Daniel Kachhap <amit.kachhap@linaro.org> wrote:

> This patch adds support for generic cpu thermal cooling low level
> implementations using frequency scaling up/down based on the registration
> parameters. Different cpu related cooling devices can be registered by the
> user and the binding of these cooling devices to the corresponding
> trip points can be easily done as the registration APIs return the
> cooling device pointer. The user of these APIs are responsible for
> passing clipping frequency . The drivers can also register to recieve
> notification about any cooling action called. Even the driver can effect
> the cooling action by modifying the default data such as freq_clip_max if
> needed.
>
>
> ...
>
> +struct cpufreq_cooling_device {
> + int id;
> + struct thermal_cooling_device *cool_dev;
> + struct freq_clip_table *tab_ptr;
> + unsigned int tab_size;
> + unsigned int cpufreq_state;
> + const struct cpumask *allowed_cpus;
> + struct list_head node;
> +};

It would be nice to document the fields. Especially id, tab_size,
cpufreq_state and node. For `node' we should describe the locking for
the list, and describe which list_head anchors this list.

> +static LIST_HEAD(cooling_cpufreq_list);
> +static DEFINE_MUTEX(cooling_cpufreq_lock);
> +static DEFINE_IDR(cpufreq_idr);
> +static DEFINE_PER_CPU(unsigned int, max_policy_freq);
> +static struct freq_clip_table *notify_table;
> +static int notify_state;
> +static BLOCKING_NOTIFIER_HEAD(cputherm_state_notifier_list);
> +
> +static int get_idr(struct idr *idr, struct mutex *lock, int *id)
> +{
> + int err;
> +again:
> + if (unlikely(idr_pre_get(idr, GFP_KERNEL) == 0))
> + return -ENOMEM;
> +
> + if (lock)
> + mutex_lock(lock);

The test for NULL `lock' is unneeded. In fact the `lock' argument
could be removed altogether - just use cooling_cpufreq_lock directly.

> + err = idr_get_new(idr, NULL, id);
> + if (lock)
> + mutex_unlock(lock);
> + if (unlikely(err == -EAGAIN))
> + goto again;
> + else if (unlikely(err))
> + return err;
> +
> + *id = *id & MAX_ID_MASK;
> + return 0;
> +}
> +
> +static void release_idr(struct idr *idr, struct mutex *lock, int id)
> +{
> + if (lock)
> + mutex_lock(lock);

Ditto.

> + idr_remove(idr, id);
> + if (lock)
> + mutex_unlock(lock);
> +}
> +
>
> ...
>
> +
> +/*Below codes defines functions to be used for cpufreq as cooling device*/
> +static bool is_cpufreq_valid(int cpu)
> +{
> + struct cpufreq_policy policy;
> + return !cpufreq_get_policy(&policy, cpu) ? true : false;

Can use

return !cpufreq_get_policy(&policy, cpu);

> +}
> +
> +static int cpufreq_apply_cooling(struct cpufreq_cooling_device *cpufreq_device,
> + unsigned long cooling_state)
> +{
> + unsigned int event, cpuid;
> + struct freq_clip_table *th_table;
> +
> + if (cooling_state > cpufreq_device->tab_size)
> + return -EINVAL;
> +
> + cpufreq_device->cpufreq_state = cooling_state;
> +
> + /*cpufreq thermal notifier uses this cpufreq device pointer*/

This code looks like it was written by two people.

/* One who does this */
/*And one who does this*/

The first one was right. Please go through all the comments in all the
patches and get the layout consistent?

> + notify_state = cooling_state;
> +
> + if (notify_state > 0) {
> + th_table = &(cpufreq_device->tab_ptr[cooling_state - 1]);
> + memcpy(notify_table, th_table, sizeof(struct freq_clip_table));
> + event = CPUFREQ_COOLING_TYPE;
> + blocking_notifier_call_chain(&cputherm_state_notifier_list,
> + event, notify_table);
> + }
> +
> + for_each_cpu(cpuid, cpufreq_device->allowed_cpus) {
> + if (is_cpufreq_valid(cpuid))
> + cpufreq_update_policy(cpuid);
> + }
> +
> + notify_state = -1;
> +
> + return 0;
> +}
> +
> +static int cpufreq_thermal_notifier(struct notifier_block *nb,
> + unsigned long event, void *data)
> +{
> + struct cpufreq_policy *policy = data;
> + unsigned long max_freq = 0;
> +
> + if ((event != CPUFREQ_ADJUST) || (notify_state == -1))

Please document `notify_state', at its definition site. This reader
doesn't know what "notify_state == -1" *means*.

> + return 0;
> +
> + if (notify_state > 0) {
> + max_freq = notify_table->freq_clip_max;
> +
> + if (per_cpu(max_policy_freq, policy->cpu) == 0)
> + per_cpu(max_policy_freq, policy->cpu) = policy->max;
> + } else {
> + if (per_cpu(max_policy_freq, policy->cpu) != 0) {
> + max_freq = per_cpu(max_policy_freq, policy->cpu);
> + per_cpu(max_policy_freq, policy->cpu) = 0;
> + } else {
> + max_freq = policy->max;
> + }
> + }
> +
> + /* Never exceed user_policy.max*/
> + if (max_freq > policy->user_policy.max)
> + max_freq = policy->user_policy.max;
> +
> + if (policy->max != max_freq)
> + cpufreq_verify_within_limits(policy, 0, max_freq);
> +
> + return 0;
> +}
> +
>
> ...
>
> +/*This cooling may be as PASSIVE/ACTIVE type*/
> +static int cpufreq_set_cur_state(struct thermal_cooling_device *cdev,
> + unsigned long state)
> +{
> + int ret = -EINVAL;
> + struct cpufreq_cooling_device *cpufreq_device;
> +
> + mutex_lock(&cooling_cpufreq_lock);
> + list_for_each_entry(cpufreq_device, &cooling_cpufreq_list, node) {
> + if (cpufreq_device && cpufreq_device->cool_dev == cdev) {
> + ret = 0;
> + break;
> + }
> + }
> + mutex_unlock(&cooling_cpufreq_lock);
> +
> + if (!ret)
> + ret = cpufreq_apply_cooling(cpufreq_device, state);

Now that we've dropped the lock, what prevents *cpufreq_device from
getting freed, or undesirably altered?

> + return ret;
> +}
> +
> +/* bind cpufreq callbacks to cpufreq cooling device */
> +static struct thermal_cooling_device_ops cpufreq_cooling_ops = {

Can it be made const?

> + .get_max_state = cpufreq_get_max_state,
> + .get_cur_state = cpufreq_get_cur_state,
> + .set_cur_state = cpufreq_set_cur_state,
> +};
> +
> +static struct notifier_block thermal_cpufreq_notifier_block = {
> + .notifier_call = cpufreq_thermal_notifier,
> +};
> +
> +struct thermal_cooling_device *cpufreq_cooling_register(
> + struct freq_clip_table *tab_ptr, unsigned int tab_size,
> + const struct cpumask *mask_val)
> +{
> + struct thermal_cooling_device *cool_dev;
> + struct cpufreq_cooling_device *cpufreq_dev = NULL;
> + unsigned int cpufreq_dev_count = 0;
> + char dev_name[THERMAL_NAME_LENGTH];
> + int ret = 0, id = 0, i;
> +
> + if (tab_ptr == NULL || tab_size == 0)
> + return ERR_PTR(-EINVAL);
> +
> + list_for_each_entry(cpufreq_dev, &cooling_cpufreq_list, node)
> + cpufreq_dev_count++;
> +
> + cpufreq_dev =
> + kzalloc(sizeof(struct cpufreq_cooling_device), GFP_KERNEL);

The 80-col contortions are ugly. Alternatives are

cpufreq_dev = kzalloc(sizeof(struct cpufreq_cooling_device),
GFP_KERNEL);

or, better,

cpufreq_dev = kzalloc(sizeof(*cpufreq_dev), GFP_KERNEL);

> + if (!cpufreq_dev)
> + return ERR_PTR(-ENOMEM);
> +
> + if (cpufreq_dev_count == 0) {
> + notify_table = kzalloc(sizeof(struct freq_clip_table),
> + GFP_KERNEL);
> + if (!notify_table) {
> + kfree(cpufreq_dev);
> + return ERR_PTR(-ENOMEM);
> + }
> + }
> +
> + cpufreq_dev->tab_ptr = tab_ptr;
> + cpufreq_dev->tab_size = tab_size;
> + cpufreq_dev->allowed_cpus = mask_val;
> +
> + /* Initialize all the tab_ptr->mask_val to the passed mask_val */
> + for (i = 0; i < tab_size; i++)
> + ((struct freq_clip_table *)&tab_ptr[i])->mask_val = mask_val;
> +
> + ret = get_idr(&cpufreq_idr, &cooling_cpufreq_lock, &cpufreq_dev->id);

hm, "get_idr" is a poor name. One would expect it to do a lookup, but
it actually does an installation. That's a result of the poorly-named
idr_get_new(), I expect.

> + if (ret) {
> + kfree(cpufreq_dev);
> + return ERR_PTR(-EINVAL);
> + }
> +
> + sprintf(dev_name, "thermal-cpufreq-%d", cpufreq_dev->id);
> +
> + cool_dev = thermal_cooling_device_register(dev_name, cpufreq_dev,
> + &cpufreq_cooling_ops);
> + if (!cool_dev) {
> + release_idr(&cpufreq_idr, &cooling_cpufreq_lock,
> + cpufreq_dev->id);
> + kfree(cpufreq_dev);
> + return ERR_PTR(-EINVAL);
> + }
> + cpufreq_dev->id = id;
> + cpufreq_dev->cool_dev = cool_dev;
> + mutex_lock(&cooling_cpufreq_lock);
> + list_add_tail(&cpufreq_dev->node, &cooling_cpufreq_list);
> + mutex_unlock(&cooling_cpufreq_lock);
> +
> + /*Register the notifier for first cpufreq cooling device*/
> + if (cpufreq_dev_count == 0)
> + cpufreq_register_notifier(&thermal_cpufreq_notifier_block,
> + CPUFREQ_POLICY_NOTIFIER);
> + return cool_dev;
> +}
> +EXPORT_SYMBOL(cpufreq_cooling_register);
> +
> +void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev)
> +{
> + struct cpufreq_cooling_device *cpufreq_dev = NULL;
> + unsigned int cpufreq_dev_count = 0;
> +
> + mutex_lock(&cooling_cpufreq_lock);
> + list_for_each_entry(cpufreq_dev, &cooling_cpufreq_list, node) {
> + if (cpufreq_dev && cpufreq_dev->cool_dev == cdev)
> + break;
> + cpufreq_dev_count++;
> + }
> +
> + if (!cpufreq_dev || cpufreq_dev->cool_dev != cdev) {
> + mutex_unlock(&cooling_cpufreq_lock);
> + return;
> + }
> +
> + list_del(&cpufreq_dev->node);
> + mutex_unlock(&cooling_cpufreq_lock);
> +
> + /*Unregister the notifier for the last cpufreq cooling device*/
> + if (cpufreq_dev_count == 1) {

But we dropped the lock, so local variable cpufreq_dev_count is now
meaningless. What prevents a race here?

> + cpufreq_unregister_notifier(&thermal_cpufreq_notifier_block,
> + CPUFREQ_POLICY_NOTIFIER);
> + kfree(notify_table);
> + }
> +
> + thermal_cooling_device_unregister(cpufreq_dev->cool_dev);
> + release_idr(&cpufreq_idr, &cooling_cpufreq_lock, cpufreq_dev->id);
> + kfree(cpufreq_dev);
> +}
> +EXPORT_SYMBOL(cpufreq_cooling_unregister);
>
> ...
>
> +struct freq_clip_table {
> + unsigned int freq_clip_max;
> + unsigned int polling_interval;
> + unsigned int temp_level;
> + const struct cpumask *mask_val;
> +};

hm, what does this thing do. Needs a nice comment for the uninitiated,
please. Something which describes the overall roles, responsibilities
and general reasons for existence.

> +int cputherm_register_notifier(struct notifier_block *nb, unsigned int list);
> +int cputherm_unregister_notifier(struct notifier_block *nb, unsigned int list);
> +
> +#ifdef CONFIG_CPU_FREQ
> +struct thermal_cooling_device *cpufreq_cooling_register(
> + struct freq_clip_table *tab_ptr, unsigned int tab_size,
> + const struct cpumask *mask_val);
> +
> +void cpufreq_cooling_unregister(struct thermal_cooling_device *cdev);
> +#else /*!CONFIG_CPU_FREQ*/

(more whacky comment layout)

>
> ...
>