Messages in this thread | | | Date | Fri, 23 Jun 2006 14:28:42 -0300 | From | "Luiz Fernando N. Capitulino" <> | Subject | Re: Serial-Core: USB-Serial port current issues. |
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On Thu, 22 Jun 2006 09:29:40 +0100 Russell King <rmk+lkml@arm.linux.org.uk> wrote:
| On Wed, Jun 21, 2006 at 06:15:13PM -0300, Luiz Fernando N. Capitulino wrote: | | > | 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? | | 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.
Neither do I. :((
I thought we could move the 'tty->hw_stopped' update to a workqueue but it has the same problem you explained above...
Greg, any suggestions?
-- 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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