Rafael J. Wysocki wrote:
> On Tuesday 21 April 2009, Michael Trimarchi wrote:
>
>> Rafael J. Wysocki wrote:
>>
>>> On Thursday 16 April 2009, Michael Trimarchi wrote:
>>>
>>>
>>>> Drivers on embedded systems would be smart enough
>>>> to know that some of the devices should remain powered up, because
>>>> they could still be useful even when the CPU wasn't running.
>>>> The patch add the in_use attribute, that it can be used by the
>>>> the drivers to avoid power down during suspend.
>>>>
>>>>
>>> OK, so the idea is that in_use will be set by the user space for devices that
>>> shouldn't be suspended. Is this correct?
>>>
>>> Assuming it is, I'd call the flag 'in_use' rather than 'is_inuse'. Also, if
>>> may_inuse is supposed to mean that we can set in_use for this device, I'd call
>>> it 'in_use_valid', I'd make it be unset by default and I'd allow the driver to
>>> unset it if it is going to react to 'in_use'.
>>>
>>>
>> is_inuse is set for the device. The may_inuse is automatically setting
>> for the child
>> device. This is done for automatically propagate the dependency
>>
>
> I see. I'd call it differently, then.
>
> Besides, is it really always the case that setting the flag for one device
> implies that the entire subtree below it should have the flag set? IOW,
> there may be some devices in the subtree that we may want to suspend anyway,
> I think.
>
>
>>>> Signed-off-by: Michael Trimarchi <trimarchi@xxxxxxxxxxxxxxxx>
>>>> Cc: "Alan Stern" <stern@xxxxxxxxxxxxxxxxxxx>
>>>> Cc: "Rafael J. Wysocki" <rjw@xxxxxxx>
>>>> Cc: "Pavel Mackek" <pavel@xxxxxx>
>>>> Cc: "Len Brown" <lenb@xxxxxxxxxx>
>>>>
>>>> ---
>>>> diff --git a/drivers/base/core.c b/drivers/base/core.c
>>>> index e73c92d..d67043b 100644
>>>> --- a/drivers/base/core.c
>>>> +++ b/drivers/base/core.c
>>>> @@ -1124,6 +1124,49 @@ static struct device *next_device(struct klist_iter *i)
>>>> }
>>>>
>>>> /**
>>>> + * device_visit_subtree - device subtree iterator.
>>>> + * @root: root struct device.
>>>> + * @data: data for the callback.
>>>> + * @fn: function to be called for each device.
>>>> + *
>>>> + * Iterate the @parent's subtree devices, and call @fn for each,
>>>> + * passing it @data.
>>>> + *
>>>> + */
>>>>
>>>>
>>> Hmm, I'm not sure ig Greg is going to like it.
>>>
>>>
>>>
>> This function walk the tree of devices following the dependences in
>> iterative mode.
>>
>
> Yes, it does, but the implementation is not the cleanest one IMO.
>
>
>>>> +void device_visit_subtree(struct device *root, void *data,
>>>> + int (*fn)(struct device *dev, void *data))
>>>> +{
>>>> + struct klist_iter i;
>>>> + struct device *parent = root;
>>>>
>>>>
>>> I'd call it 'current' or 'cur';
>>>
>>>
>>>
>> ok
>>
>>>> + struct device *child = NULL;
>>>> + int error;
>>>> +
>>>> + klist_iter_init(&parent->p->klist_children, &i);
>>>> +move_down:
>>>> + error = fn(parent, data);
>>>> + if (error && parent != root)
>>>>
>>>>
>>> Shouldn't the iteration break on error?
>>>
>>>
>>>
>> The iteration don't break on error because, the return just said that the
>> subtree is just enable
>>
>
> You're assuming that _your_ function will be the only one called via this one,
> but in that case why do you introduce a generic low level helper?
>
>
>>>> + goto move_up;
>>>> +
>>>> + pr_debug("device: '%s': %s\n", dev_name(parent), __func__);
>>>> +
>>>> + child = next_device(&i);
>>>> + if (child) {
>>>> + parent = child;
>>>> + goto move_down;
>>>> + }
>>>> +move_up:
>>>> + klist_iter_exit(&i);
>>>> + if (parent != root) {
>>>> + klist_iter_init_node(&parent->parent->p->klist_children, &i,
>>>> + &parent->p->knode_parent);
>>>> + parent = next_device(&i);
>>>> + if (parent)
>>>> + goto move_down;
>>>> + klist_iter_exit(&i);
>>>> + }
>>>>
>>>>
>>> Please find a way to reduce the number of gotos in this function.
>>>
>>> Besides, I'm not sure if it's really necessary. What's wrong with using
>>> simply device_for_each_child() instead?
>>>
>>>
>> Just to have an iterative function
>>
>
> Care to elaborate?
>
>
>>>
>>>
>>>> +}
>>>> +
>>>> +/**
>>>> * device_for_each_child - device child iterator.
>>>> * @parent: parent struct device.
>>>> * @data: data for the callback.
>>>> @@ -1207,6 +1250,7 @@ int __init devices_init(void)
>>>> return -ENOMEM;
>>>> }
>>>>
>>>> +EXPORT_SYMBOL_GPL(device_visit_subtree);
>>>> EXPORT_SYMBOL_GPL(device_for_each_child);
>>>> EXPORT_SYMBOL_GPL(device_find_child);
>>>>
>>>> diff --git a/drivers/base/power/main.c b/drivers/base/power/main.c
>>>> index 69b4ddb..00ad150 100644
>>>> --- a/drivers/base/power/main.c
>>>> +++ b/drivers/base/power/main.c
>>>> @@ -64,6 +64,45 @@ void device_pm_unlock(void)
>>>> mutex_unlock(&dpm_list_mtx);
>>>> }
>>>>
>>>> +int device_set_may_inuse_enable(struct device *dev, void *data)
>>>>
>>>>
>>> What exactly is the purpose of this function?
>>>
>>>
>>>
>> This function said that the parent is used by a driver
>>
>>>> +{
>>>> + pr_debug("PM: Device change in use status: %s\n", dev_name(dev));
>>>> +
>>>> + /* if the device is suspend the subtree is in may_suspend status */
>>>> + if (dev->power.is_inuse)
>>>> + goto out;
>>>>
>>>>
>>> return 1; ?
>>>
>>>
>>>
>>>> +
>>>> + dev->power.may_inuse = (unsigned int)data;
>>>>
>>>>
>>> Can this conversion be avoided?
>>>
>>>
>>>
>>>> + return 0;
>>>> +out:
>>>> + /* cut the entire subtree */
>>>> + return 1;
>>>> +}
>>>> +
>>>> +/**
>>>> + * device_set_inuse_enable - Mark the device as used by userspace
>>>> + * application
>>>> + */
>>>> +int device_set_inuse_enable(struct device *dev, int enable)
>>>>
>>>>
>>> We have bool for things like 'enable'.
>>>
>>>
>>>
>> ok
>>
>>>> +{
>>>> + mutex_lock(&dpm_list_mtx);
>>>> +
>>>> + /* the new status is equal the old one */
>>>> + if (dev->power.is_inuse == enable)
>>>> + goto out;
>>>> +
>>>> + dev->power.is_inuse = enable;
>>>> +
>>>> + /* Update device children to set the in use status */
>>>> + device_visit_subtree(dev, (void *)enable,
>>>> + device_set_may_inuse_enable);
>>>>
>>>>
>>> Why not do:
>>>
>>> if (dev->power.in_use != enable) {
>>> dev->power.in_use = enable;
>>> device_visit_subtree(dev, (void *)enable, device_set_may_inuse_enable);
>>> }
>>>
>>> Also, I think this 'enable' conversion isn't really necessary. You can use two
>>> separate helper functions for setting and unsetting and pass NULL as the second
>>> argument.
>>>
>>>
>>>
>> ok
>>
>>>> +
>>>> +out:
>>>> + mutex_unlock(&dpm_list_mtx);
>>>> + return 0;
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(device_set_inuse_enable);
>>>> +
>>>> /**
>>>> * device_pm_add - add a device to the list of active devices
>>>> * @dev: Device to be added to the list
>>>> @@ -78,6 +117,13 @@ void device_pm_add(struct device *dev)
>>>> if (dev->parent->power.status >= DPM_SUSPENDING)
>>>> dev_warn(dev, "parent %s should not be sleeping\n",
>>>> dev_name(dev->parent));
>>>> + if (device_is_inuse(dev->parent)) {
>>>> + mutex_unlock(&dpm_list_mtx);
>>>> + /* if the parent has suspend disable, propagate it
>>>> + * to the new child */
>>>> + device_set_may_inuse_enable(dev, (void *)1);
>>>>
>>>>
>>> The conversion is just terrible. I'd very much prefer it to be
>>> device_set_in_use_possible_enable(dev, true).
>>>
>>>
>>>
>> ok
>>
>>>> + mutex_lock(&dpm_list_mtx);
>>>> + }
>>>> } else if (transition_started) {
>>>> /*
>>>> * We refuse to register parentless devices while a PM
>>>> diff --git a/drivers/base/power/power.h b/drivers/base/power/power.h
>>>> index c7cb4fc..e7d21bb 100644
>>>> --- a/drivers/base/power/power.h
>>>> +++ b/drivers/base/power/power.h
>>>> @@ -3,6 +3,11 @@ static inline void device_pm_init(struct device *dev)
>>>> dev->power.status = DPM_ON;
>>>> }
>>>>
>>>> +static inline int device_is_inuse(struct device *dev)
>>>> +{
>>>> + return dev->power.is_inuse || dev->power.may_inuse;
>>>> +}
>>>>
>>>>
>>> OK, so what's the meaning of is_inuse and may_inuse?
>>>
>>>
>>>
>> Maybe the idea is if the parent is in_use the child are may_inuse so
>> they are potentialy in
>> use. The user can disable a tree and after reanable a child.
>>
>
> So I'd call the flag subtree_in_use or better subtree_no_suspend, then.
>
If you say just subtree is in use, you have this case:
A in_use ---> A1 may_inuse----->A4 may_inuse---- A6 no_in_use
| |
\----> A2 \ --A7 may_inuse ---- A5 no_in_use
|
\----> A3
The user do echo "enabled" > in_use for device A
A1, A2, A4, A6, A7, A5 go in may_inuse state.
The user space can check that the device is in_use. it does't know is for
an in_use or may_inuse condition but it doesnt metter because the user space
can change for example the A5 and A6 and give the graph above. This is
the recursion
issue.
> Moreover, you don't really have to propagate the no_suspend bit down the
> device tree when the flag is set for a device. You can simply modify the
> prepare phase of suspend to check if the current device's parent has
> no_suspend or subtree_no_suspend set and to set that for the current device
> if so (or clear otherwise).
>
If I understand we don't want that this flag change the pm transition.
> Thanks,
> Rafael
>
>
Michael
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