On Mon, 31 Jan 2011 12:33:41 +0200 Ohad Ben-Cohen <ohad@xxxxxxxxxx> wrote: > Add a 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. > > Signed-off-by: Ohad Ben-Cohen <ohad@xxxxxxxxxx> > Cc: Hari Kanigeri <h-kanigeri2@xxxxxx> > Cc: Benoit Cousson <b-cousson@xxxxxx> > Cc: Kevin Hilman <khilman@xxxxxx> > Cc: Grant Likely <grant.likely@xxxxxxxxxxxx> > Cc: Arnd Bergmann <arnd@xxxxxxxx> > Cc: Paul Walmsley <paul@xxxxxxxxx> > Acked-by: Tony Lindgren <tony@xxxxxxxxxxx> > --- > Documentation/hwspinlock.txt | 299 ++++++++++++++++++ > drivers/Kconfig | 2 + > drivers/Makefile | 2 + > drivers/hwspinlock/Kconfig | 13 + > drivers/hwspinlock/Makefile | 5 + > drivers/hwspinlock/hwspinlock.h | 61 ++++ > drivers/hwspinlock/hwspinlock_core.c | 557 ++++++++++++++++++++++++++++++++++ > include/linux/hwspinlock.h | 298 ++++++++++++++++++ It's a little irritating having two hwspinlock.h's. hwspinlock_internal.h wold be a conventional approach. But it's not a big deal. > > ... > > +/* > + * A radix tree is used to maintain the available hwspinlock instances. > + * The tree associates hwspinlock pointers with their integer key id, > + * and provides easy-to-use API which makes the hwspinlock core code simple > + * and easy to read. > + * > + * Radix trees are quick on lookups, and reasonably efficient in terms of > + * storage, especially with high density usages such as this framework > + * requires (a continuous range of integer keys, beginning with zero, is > + * used as the ID's of the hwspinlock instances). > + * > + * The radix tree API supports tagging items in the tree, which this > + * framework uses to mark unused hwspinlock instances (see the > + * HWSPINLOCK_UNUSED tag above). As a result, the process of querying the > + * tree, looking for an unused hwspinlock instance, is now reduced to a > + * single radix tree API call. > + */ Nice comment! > +static RADIX_TREE(hwspinlock_tree, GFP_KERNEL); > + > > ... > > +/** > + * __hwspin_lock_timeout() - lock an hwspinlock with timeout limit > + * @hwlock: the hwspinlock to be locked > + * @timeout: timeout value in jiffies hm, why in jiffies? The problem here is that lazy programmers will use hwspin_lock_timeout(lock, 10, ...) and their code will work happily with HZ=100 but will explode with HZ=1000. IOW, this interface *requires* that all callers perform a seconds-to-jiffies conversion before calling hwspin_lock_timeout(). So why not reduce their effort and their ability to make mistakes by defining the API to take seconds? > + * @mode: mode which controls whether local interrupts are disabled or not > + * @flags: a pointer to where the caller's interrupt state will be saved at (if > + * requested) > + * > + * This function locks the given @hwlock. If the @hwlock > + * is already taken, the function will busy loop waiting for it to > + * be released, but give up when @timeout jiffies have elapsed. If @timeout > + * is %MAX_SCHEDULE_TIMEOUT, the function will never give up (therefore if a > + * faulty remote core never releases the @hwlock, it will deadlock). > + * > + * Upon a successful return from this function, preemption is disabled > + * (and possibly local interrupts, too), so the caller must not sleep, > + * and is advised to release the hwspinlock as soon as possible. > + * This is required in order to minimize remote cores polling on the > + * hardware interconnect. > + * > + * The user decides whether local interrupts are disabled or not, and if yes, > + * whether he wants their previous state to be saved. It is up to the user > + * to choose the appropriate @mode of operation, exactly the same way users > + * should decide between spin_lock, spin_lock_irq and spin_lock_irqsave. > + * > + * Returns 0 when the @hwlock was successfully taken, and an appropriate > + * error code otherwise (most notably -ETIMEDOUT if the @hwlock is still > + * busy after @timeout meets jiffies). The function will never sleep. > + */ > > ... > -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
