On Jun 1, 2005, at 16:19, Stephen Hemminger wrote: > Andy Fleming wrote: >> >> But not this one. The phy_read and phy_write functions are >> reading from and writing to a bus. It is a reasonable >> implementation to have the operation block in the bus driver, and >> be awoken when an interrupt signals the operation is done. All >> of the phydev spinlocks have been arranged so as to prevent the >> lock being taken during interrupt time. >> >> Unless I've misunderstood spinlocks (it wouldn't be the first >> time), as long as the lock is never taken in interrupt time, it >> should be ok to hold the lock, and wait for an interrupt before >> clearing the lock. >> > > > The problem is that sleeping is defined in the linux kernel as > meaning waiting on a mutual exclusion > primitive (like semaphore) that puts the current thread to sleep. > It is not legal to sleep with a spinlock held. > In the phy_read code you do: > spin_lock_bh(&bus->mdio_lock); > retval = bus->read(bus, phydev->addr, regnum); > spin_unlock_bh(&bus->mdio_lock); > > If the bus->read function were to do something like start a request > and wait on a semaphore, then > you would be sleeping with a spin lock held. So bus->read can not > sleep! (as sleep is defined in the > linux kernel).
Hmm... I understand this reasoning, but I still need a way for a bus read to wait for an interrupt before returning. I suppose I can just have the code spin while it waits, but that seems wrong, somehow. I'm open to any suggestions.
