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SubjectRe: [PATCH v2 1/4] drivers: hwspinlock: add generic framework
* Ohad Ben-Cohen <ohad@wizery.com> [101123 07:27]:
> Add a common, platform-independent, hwspinlock framework.
>
> Hardware spinlock devices are needed, e.g., in order to access data
> that is shared between remote processors, that otherwise have no
> alternative mechanism to accomplish synchronization and mutual exclusion
> operations.

<snip>

> + int hwspin_lock(struct hwspinlock *hwlock);
> + - lock a previously assigned hwspinlock. If the hwspinlock is already
> + taken, the function will busy loop waiting for it to be released.
> + Note: if a faulty remote core never releases this lock, this function
> + will deadlock.
> + This function will fail only if hwlock is invalid. Otherwise, it will
> + always succeed (or deadlock; see above) and it will never sleep.
> + Upon a successful return from this function, preemption is disabled so
> + the caller must not sleep, and is advised to release the hwspinlock as
> + soon as possible, in order to minimize remote cores polling on the
> + hardware interconnect.
...

> + int hwspin_lock_timeout(struct hwspinlock *hwlock, unsigned long timeout);
> + - lock a previously-assigned hwspinlock with a timeout limit (specified in
> + jiffies). If the hwspinlock is already taken, the function will busy loop
> + waiting for it to be released, but give up when the timeout meets jiffies.
> + If timeout is 0, the function will never give up (therefore if a faulty
> + remote core never releases the hwspinlock, it will deadlock).
> + Upon a successful return from this function, preemption is disabled so
> + the caller must not sleep, and is advised to release the hwspinlock as
> + soon as possible, in order to minimize remote cores polling on the
> + hardware interconnect.
> + Returns 0 when successful and an appropriate error code otherwise (most
> + notably -ETIMEDOUT if the hwspinlock is still busy after timeout meets
> + jiffies). The function will never sleep.

Do we even need the hwspin_lock variants, why can't we always use the
hwspin_lock_timeout variants?

To me the idea of looping waiting for some external system to release
a lock is not a good idea..

Regards,

Tony


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