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.
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