Messages in this thread |  | | | Date | Tue, 4 Jul 2006 16:42:57 -0300 | | From | "Luiz Fernando N. Capitulino" <> | | Subject | Re: Serial-Core: USB-Serial port current issues. |
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Hi Paul,
On Mon, 26 Jun 2006 19:49:09 -0500 Paul Fulghum <paulkf@microgate.com> 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 <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)
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 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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