Hi Paul,
On Mon, 26 Jun 2006 19:49:09 -0500
Paul Fulghum <[email protected]> wrote:
| 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 <[email protected]> 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)
What's the problem with get_mctrl() being called from IRQ?
Note that get_mctrl() is a callback and the driver is free to call _its_
get_mctrl() from IRQ if it wants to.
| 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
Well, I think it'd work. But how can we keep track of 'icount'?
Should the driver add 1 if it updates 'tty->hw_stopped'?
PS: Sorry for the long delay, I was off last week.
--
Luiz Fernando N. Capitulino
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