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Date: Sat, 2 Jul 2011 23:56:24 +0200
From: "Rafael J. Wysocki" <rjw@...k.pl>
To: MyungJoo Ham <myungjoo.ham@...sung.com>
Cc: linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
Len Brown <len.brown@...el.com>, Pavel Machek <pavel@....cz>,
"Greg Kroah-Hartman" <gregkh@...e.de>,
Kyungmin Park <kyungmin.park@...sung.com>,
Jiejing Zhang <kzjeef@...il.com>,
Colin Cross <ccross@...gle.com>, Nishanth Menon <nm@...com>,
Thomas Gleixner <tglx@...utronix.de>, myungjoo.ham@...il.com
Subject: Re: [PATCH v3 1/3] PM: Introduce DEVFREQ: generic DVFS framework with device-specific OPPs
Hi,
I'm not sure if spelling DEVFREQ in the kerneldoc comments with capitals is
a good idea, it looks kind of odd. I'm not sure what would be look better,
though.
On Friday, May 27, 2011, MyungJoo Ham wrote:
...
> +/**
> + * devfreq_monitor() - Regularly run devfreq_do() and support device DEVFREQ tickle.
I'd say "periodically" istead of "regularly".
> + * @work: the work struct used to run devfreq_monitor periodically.
Also please say something more about the "tickle" thinkg here.
> + */
> +static void devfreq_monitor(struct work_struct *work)
> +{
> + struct devfreq *devfreq;
> + int error;
> + bool continue_polling = false;
> + struct devfreq *to_remove = NULL;
> +
> + mutex_lock(&devfreq_list_lock);
> +
> + list_for_each_entry(devfreq, &devfreq_list, node) {
> + /* Remove the devfreq entry that failed */
> + if (to_remove) {
> + list_del(&to_remove->node);
> + kfree(to_remove);
> + to_remove = NULL;
> + }
> +
> + /*
> + * If the device is tickled and the tickle duration is left,
> + * do not change the frequency for a while
> + */
> + if (devfreq->tickle) {
> + continue_polling = true;
> + devfreq->tickle--;
> +
> + /*
> + * If the tickle is ending and the device is not going
> + * to poll, force the device to poll next time so that
> + * it can return to the original frequency afterwards.
> + * However, non-polling device will have 0 polling_ms,
> + * it will not poll again later.
> + */
> + if (devfreq->tickle == 0 && devfreq->next_polling == 0)
> + devfreq->next_polling = 1;
> +
> + continue;
> + }
> +
> + /* This device does not require polling */
> + if (devfreq->next_polling == 0)
> + continue;
> +
> + continue_polling = true;
> +
> + if (devfreq->next_polling == 1) {
> + /* This device is polling this time */
I'd remove this comment, it's confusing IMO. Besides, it may be better
to structure the code like this:
if (devfreq->next_polling-- == 1) {
}
and then you wouldn't need the "else" at all.
> + error = devfreq_do(devfreq);
> + if (error && error != -EAGAIN) {
> + /*
> + * Remove a devfreq with error. However,
> + * We cannot remove it right here because the
Comma after "here", please.
> + * devfreq pointer is going to be used by
> + * list_for_each_entry above. Thus, it is
> + * removed afterwards.
Why don't you use list_for_each_entry_safe(), then?
> + */
> + to_remove = devfreq->dev;
> + dev_err(devfreq->dev, "devfreq_do error(%d). "
> + "DEVFREQ is removed from the device\n",
> + error);
> + continue;
> + }
> + devfreq->next_polling = DIV_ROUND_UP(
> + devfreq->profile->polling_ms,
> + DEVFREQ_INTERVAL);
> + } else {
> + /* The device will poll later when next_polling = 1 */
> + devfreq->next_polling--;
> + }
> + }
> +
> + if (to_remove) {
> + list_del(&to_remove->node);
> + kfree(to_remove);
> + to_remove = NULL;
> + }
> +
> + if (continue_polling) {
> + polling = true;
> + queue_delayed_work(devfreq_wq, &devfreq_work,
> + msecs_to_jiffies(DEVFREQ_INTERVAL));
> + } else {
> + polling = false;
> + }
OK, so why exactly continue_polling is needed? It seems you might siply use
"polling" instead of it above.
> +
> + mutex_unlock(&devfreq_list_lock);
> +}
...
> +/**
> + * devfreq_update() - Notify that the device OPP has been changed.
> + * @dev: the device whose OPP has been changed.
> + * @may_not_exist: do not print error message even if the device
> + * does not have devfreq entry.
This argument isn't used any more.
> + */
> +int devfreq_update(struct device *dev)
> +{
> + struct devfreq *devfreq;
> + int err = 0;
> +
> + mutex_lock(&devfreq_list_lock);
> +
> + devfreq = find_device_devfreq(dev);
> + if (IS_ERR(devfreq)) {
> + err = PTR_ERR(devfreq);
> + goto out;
> + }
> +
> + if (devfreq->tickle) {
> + /* If the max freq available is changed, re-tickle */
It would be good to explain what "re-tickle" means.
> + unsigned long freq = devfreq->profile->max_freq;
> + struct opp *opp = opp_find_freq_floor(devfreq->dev, &freq);
> +
> + if (IS_ERR(opp)) {
> + err = PTR_ERR(opp);
> + goto out;
> + }
> +
> + /* Max freq available is not changed */
> + if (devfreq->previous_freq == freq)
> + goto out;
> +
> + err = devfreq->profile->target(devfreq->dev, opp);
> + if (!err)
> + devfreq->previous_freq = freq;
Why don't we run devfreq_do() in this case?
> + } else {
> + /* Reevaluate the proper frequency */
> + err = devfreq_do(devfreq);
> + }
> +
> +out:
> + mutex_unlock(&devfreq_list_lock);
> + return err;
> +}
> +
Add a kerneldoc comment here, please.
> +static int _devfreq_tickle_device(struct devfreq *df, unsigned long delay)
> +{
> + int err = 0;
> + unsigned long freq;
> + struct opp *opp;
> +
> + freq = df->profile->max_freq;
> + opp = opp_find_freq_floor(df->dev, &freq);
> + if (IS_ERR(opp))
> + return PTR_ERR(opp);
> +
> + if (df->previous_freq != freq) {
> + err = df->profile->target(df->dev, opp);
> + if (!err)
> + df->previous_freq = freq;
> + }
> + if (err) {
> + dev_err(df->dev, "%s: Cannot set frequency.\n", __func__);
> + } else {
> + df->tickle = delay;
> + df->num_tickle++;
> + }
> +
> + if (devfreq_wq && !polling) {
> + polling = true;
> + queue_delayed_work(devfreq_wq, &devfreq_work,
> + msecs_to_jiffies(DEVFREQ_INTERVAL));
> + }
> +
> + return err;
> +}
Thanks,
Rafael
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