Hi Paul,
On Mon, Jan 16, 2012 at 9:04 PM, Paul Walmsley <paul@xxxxxxxxx> wrote:
> Hi
>
> On Mon, 16 Jan 2012, Jean Pihet wrote:
>
>> Speaking of the locking, currently a spinlock is used and it could be
>> replaced by a more efficient mutex. This is ok at the condition that
>> this code is not called from interrupt context?
>>
>> Kevin,
>> Do you know if the per-device constraint code can be called from
>> interrupt context?
>
> It can't be. It uses a mutex itself. So a mutex is what we want. Take a
> look at drivers/base/power/qos.c:dev_pm_qos_update_request() (included
> below)
Ok thanks for checking, I should have done it before asking ;-|
Jean
>
>
> - Paul
>
>
> /**
> * dev_pm_qos_update_request - modifies an existing qos request
> * @req : handle to list element holding a dev_pm_qos request to use
> * @new_value: defines the qos request
> *
> * Updates an existing dev PM qos request along with updating the
> * target value.
> *
> * Attempts are made to make this code callable on hot code paths.
> *
> * Returns 1 if the aggregated constraint value has changed,
> * 0 if the aggregated constraint value has not changed,
> * -EINVAL in case of wrong parameters, -ENODEV if the device has been
> * removed from the system
> */
> int dev_pm_qos_update_request(struct dev_pm_qos_request *req,
> s32 new_value)
> {
> int ret = 0;
>
> if (!req) /*guard against callers passing in null */
> return -EINVAL;
>
> if (WARN(!dev_pm_qos_request_active(req),
> "%s() called for unknown object\n", __func__))
> return -EINVAL;
>
> mutex_lock(&dev_pm_qos_mtx);
>
> if (req->dev->power.constraints) {
> if (new_value != req->node.prio)
> ret = apply_constraint(req, PM_QOS_UPDATE_REQ,
> new_value);
> } else {
> /* Return if the device has been removed */
> ret = -ENODEV;
> }
>
> mutex_unlock(&dev_pm_qos_mtx);
> return ret;
> }
>
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