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Date: Wed, 9 May 2012 13:57:01 +0530
Message-ID: <CAK44p20fjH7B8O3whMXh8C+X2nQ31=Sx5iNqW8LHrfOWUt_VpA@mail.gmail.com>
Subject: Re: [PATCH v3 2/6] thermal: Add generic cpufreq cooling implementation
From: Amit Kachhap <amit.kachhap@linaro.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: linux-pm@lists.linux-foundation.org, durgadoss.r@intel.com,
        linux-acpi@vger.kernel.org, lenb@kernel.org, rui.zhang@intel.com,
        linaro-dev@lists.linaro.org, linux-kernel@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, patches@linaro.org
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On 9 May 2012 01:46, Andrew Morton <akpm@linux-foundation.org> wrote:
> 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.

Thanks Andrew for the detailed review. I will add more documentation
and post the next version shortly.
>
>> +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.
Agreed
>
>> + ? ? 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
Ok
>
> ? ? ? ?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?
Sure will add more details.
>
>
>> + ? ? 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?
Agreed the lock can be put over the entire funtion.
>
>> + ? ? return ret;
>> +}
>> +
>> +/* bind cpufreq callbacks to cpufreq cooling device */
>> +static struct thermal_cooling_device_ops cpufreq_cooling_ops = {
>
> Can it be made const?
Yes it can be made const as it is unmodified.
>
>> + ? ? .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);

Ok will use shorter variables.
>
>
>> + ? ? 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?
Yes lock can be extended to include it.
>
>> + ? ? ? ? ? ? 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.
Ok
>
>> +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)
>
>>
>> ...
>>
>
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