Re: Serial-Core: USB-Serial port current issues.

["Luiz Fernando N. Capitulino" <lcapitulino@mandriva.com.br>]

On Wed, 21 Jun 2006 17:43:36 +0100
Russell King <rmk+lkml@arm.linux.org.uk> wrote:

| In the uart_update_mctrl() case, the purpose of the locking is to
| prevent two concurrent changes to the modem control state resulting
| in an inconsistency between the hardware and the software state.  If
| it's provable that it is always called from process context (and
| it isn't called from a lock_kernel()-section or the lock_kernel()
| section doesn't mind a rescheduling point being introduced there),
| there's no problem converting that to a mutex.

 Ok, then I can submit my debug patch to answer these questions.

 might_sleep() can catch the lock_kernel()-section case right?

| With get_mctrl(), the situation is slightly more complicated, because
| we need to atomically update tty->hw_stopped in some circumstances
| (that may also be modified from irq context.)  Therefore, to give
| the driver a consistent locking picture, the spinlock is _always_
| held.

 Is it too bad (wrong?) to only protect the tty->hw_stopped update
by the spinlock? Then the call to get_mctrl() could be protected by
a mutex, or is it messy?

-- 
Luiz Fernando N. Capitulino