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SubjectRe: Serial-Core: USB-Serial port current issues.
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On Mon, 2006-06-26 at 15:26 -0700, Greg KH wrote:
> On Fri, Jun 23, 2006 at 02:28:42PM -0300, Luiz Fernando N. Capitulino wrote:
> > On Thu, 22 Jun 2006 09:29:40 +0100
> > Russell King <rmk+lkml@arm.linux.org.uk> wrote:
> >
> > |
> > | Consider this scenario with what you're proposing:
> > |
> > | thread irq
> > |
> > | take mutex
> > | get_mctrl
> > | cts changes state
> > | take port lock
> > | mctrl state read
> > | tty->hw_stopped changed state
> > | release port lock
> > | releaes mutex
> > | take port lock
> > | update tty->hw_stopped
> > | release port lock
> > |
> > | Now, tty->hw_stopped does not reflect the hardware state, which will be
> > | buggy and can cause a loss of transmission.
> > |
> > | I'm not sure what to suggest on this one since for USB drivers you do
> > | need to be able to sleep in this method... but for UARTs you must not.

What about this ugly fragment?
(assuming get_mctrl not called from IRQ)

take mutex
take port lock
again:
save local copy of icount
release port lock
get_mctrl
take port lock
if (icount changed)
goto again
update tty->hw_stopped
release port lock
release mutex
--
Paul





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