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SubjectRe: [PATCH update] PM: Introduce core framework for run-time PM of I/O devices (rev. 12)
On Wed, 5 Aug 2009, Rafael J. Wysocki wrote:

> Hi,
>
> The patch below should address all of your recent comments.
>
> Additionally I changed a few bits that I thought could turn out to be
> problematic at one point.

Looking good. I've got a few more suggestions.

It occurred to me that there's no need for a separate
"runtime_failure" flag. A nonzero value of "last_error" will do just
as well. If you make this change, note that it affects the
documentation as well as the code.

If we defer a resume request while a suspend is in progress, then when
the suspend finishes should the resume be carried out immediately
rather than queued? I don't see any reason why not.


> +/**
> + * __pm_runtime_suspend - Carry out run-time suspend of given device.
> + * @dev: Device to suspend.
> + * @from_wq: If set, the function has been called via pm_wq.
> + *
> + * Check if the device can be suspended and run the ->runtime_suspend() callback
> + * provided by its bus type. If another suspend has been started earlier, wait
> + * for it to finish. If there's an idle notification pending, cancel it. If
> + * there's a suspend request scheduled while this function is running and @sync
> + * is 'true', cancel that request.

Change the last two sentences as follows: If an idle notification or suspend
request is pending or scheduled, cancel it.

> + *
> + * This function must be called under dev->power.lock with interrupts disabled.
> + */
> +int __pm_runtime_suspend(struct device *dev, bool from_wq)
> + __releases(&dev->power.lock) __acquires(&dev->power.lock)
> +{
...
> + pm_runtime_deactivate_timer(dev);
> +
> + if (dev->power.request_pending) {
> + /* Pending resume requests take precedence over us. */
> + if (dev->power.request == RPM_REQ_RESUME)
> + return -EAGAIN;
> + /* Other pending requests need to be canceled. */
> + dev->power.request = RPM_REQ_NONE;
> + }

Might as well use pm_runtime_cancel_pending since we have it:

/* Pending resume requests take precedence over us. */
if (dev->power.request_pending && dev->power.request == RPM_REQ_RESUME)
return -EAGAIN;
/* Other pending requests need to be canceled. */
pm_runtime_cancel_pending(dev);
...
> + if (dev->power.deferred_resume) {
> + __pm_request_resume(dev);

__pm_runtime_resume instead?


> +/**
> + * __pm_runtime_resume - Carry out run-time resume of given device.
> + * @dev: Device to resume.
> + * @from_wq: If set, the function has been called via pm_wq.
> + *
> + * Check if the device can be woken up and run the ->runtime_resume() callback
> + * provided by its bus type. If another resume has been started earlier, wait
> + * for it to finish. If there's a suspend running in parallel with this
> + * function, wait for it to finish and resume the device. If there's a suspend
> + * request or idle notification pending, cancel it. If there's a resume request
> + * scheduled while this function is running, cancel that request.

Change the last two sentences as follows: Cancel any pending requests.

> + *
> + * This function must be called under dev->power.lock with interrupts disabled.
> + */
> +int __pm_runtime_resume(struct device *dev, bool from_wq)
> + __releases(&dev->power.lock) __acquires(&dev->power.lock)
> +{
> + struct device *parent = NULL;
> + int retval = 0;
> +
> + repeat:
> + if (dev->power.runtime_failure)
> + return -EINVAL;

Here and in two places below, goto out_parent instead of returning
directly.

...
> + if (!parent && dev->parent) {
> + /*
> + * Increment the parent's resume counter and resume it if
> + * necessary.
> + */
> + parent = dev->parent;
> + spin_unlock_irq(&dev->power.lock);
> +
> + retval = pm_runtime_get_sync(parent);
> +
> + spin_lock_irq(&dev->power.lock);
> + /* We can resume if the parent's run-time PM is disabled. */
> + if (retval < 0 && retval != -EAGAIN)
> + goto out_parent;

Instead of checking retval, how about checking the parent's PM status?
Also, this isn't needed if the parent is set to ignore children.


> +static int __pm_request_idle(struct device *dev)
> +{
> + int retval = 0;
> +
> + if (dev->power.runtime_failure)
> + retval = -EINVAL;
> + else if (atomic_read(&dev->power.usage_count) > 0
> + || dev->power.disable_depth > 0
> + || dev->power.timer_expires > 0

This line should be removed.

...
> + if (dev->power.request_pending && dev->power.request != RPM_REQ_NONE) {
> + /* Any requests other then RPM_REQ_IDLE take precedence. */
> + if (dev->power.request != RPM_REQ_IDLE)
> + retval = -EAGAIN;
> + return retval;
> + }
> +
> + dev->power.request = RPM_REQ_IDLE;
> + if (dev->power.request_pending)
> + return retval;
> +
> + dev->power.request_pending = true;
> + queue_work(pm_wq, &dev->power.work);

This should be done consistently with the other routines. Thus:

if (dev->power.request_pending) {
/* All other requests take precedence. */
if (dev->power.request == RPM_REQ_NONE)
dev->power.request = RPM_REQ_IDLE;
else if (dev->power.request != RPM_REQ_IDLE)
retval = -EAGAIN;
return retval;
}
dev->power.request = RPM_REQ_IDLE;
dev->power.request_pending = true;
queue_work(pm_wq, &dev->power.work);


> +int __pm_runtime_set_status(struct device *dev, unsigned int status)
> +{
> + struct device *parent = dev->parent;
> + unsigned long flags;
> + bool notify_parent = false;
> + int error = 0;
> +
> + if (status != RPM_ACTIVE && status != RPM_SUSPENDED)
> + return -EINVAL;
> +
> + spin_lock_irqsave(&dev->power.lock, flags);
> +
> + if (!dev->power.runtime_failure && !dev->power.disable_depth)
> + goto out;

Set "error" to a negative code?


> @@ -757,11 +770,16 @@ static int dpm_prepare(pm_message_t stat
> dev->power.status = DPM_PREPARING;
> mutex_unlock(&dpm_list_mtx);
>
> - error = device_prepare(dev, state);
> + if (pm_runtime_disable(dev) && device_may_wakeup(dev))
> + /* Wake-up during suspend. */
> + error = -EBUSY;

Or maybe "Wakeup was requested during sleep transition."


> + unsigned int deferred_resume;
> + - set if ->runtime_resume() is about to be run while ->runtime_suspend() is
> + being executed for that device and it is not practical to wait for the
> + suspend to complete; means "queue up a resume request as soon as you've
> + suspended"

"start a resume" instead of "queue up a resume request"?


> +5. Run-time PM Initialization
...
> +If the defaul initial run-time PM status of the device (i.e. 'suspended')

Fix spelling of "default".

> +reflects the actual state of the device, its bus type's or its driver's
> +->probe() callback will likely need to wake it up using one of the PM core's
> +helper functions described in Section 4. In that case, pm_runtime_resume()
> +should be used. Of course, for this purpose the device's run-time PM has to be
> +enabled earlier by calling pm_runtime_enable().
> +
> +If ->probe() calls pm_runtime_suspend() or pm_runtime_idle(), or their
> +asynchronous counterparts, they will fail returning -EAGAIN, because the
> +device's usage counter is incremented by the core before executing ->probe().
> +Still, it may be desirable to suspend the device as soon as ->probe() has
> +finished, so the core uses pm_runtime_idle() to invoke the device bus type's
> +->runtime_idle() callback at that time, which only happens even if ->probe()

s/which only happens even/but only/

> +is successful.

Alan Stern



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