On Wed, 23 Nov 2005 09:56:33 -0200
Eduardo Pereira Habkost <[email protected]> wrote:
| On Wed, Nov 23, 2005 at 09:36:55AM -0200, Luiz Fernando Capitulino wrote:
| > On Tue, 22 Nov 2005 14:13:53 -0800
| > Greg KH <[email protected]> wrote:
| >
| > | On Tue, Nov 22, 2005 at 07:59:26PM -0200, Luiz Fernando Capitulino wrote:
| > | > @@ -60,6 +61,7 @@ struct usb_serial_port {
| > | > struct usb_serial * serial;
| > | > struct tty_struct * tty;
| > | > spinlock_t lock;
| > | > + struct semaphore sem;
| > |
| > | You forgot to document what this semaphore is used for.
| >
| > Okay.
| >
| > | Hm, can we just use the spinlock already present in the port structure
| > | for this? Well, drop the spinlock and use the semaphore? Yeah, that
| > | means grabbing a semaphore for ever write for some devices, but USB data
| > | rates are slow enough it wouldn't matter :)
| >
| > As far as I read the code, I found that spinlock is only used by the
| > generic driver, in the
| > drivers/usb/serial/generic.c:usb_serial_generic_write() function.
| >
| > Can we drop the spinlock there and use our new semaphore? Or should we
| > create a new spinlock just to use there?
|
| The spin_lock is used only to protect write_urb_busy. An atomic_t seem
| to be more appropriate for it. If we do that, I guess we can remove the
| (then unused) spinlock.
Ok, but, hmm.. I found the spinklock is actually used by other drivers too.
I didn't catch this before because I wasn't compiling then. Sorry, my fault.
| So we have three proposed changes:
|
| - Add semaphore to serialize close()/open() (properly documented)
| - Replace write_urb_busy with an atomic_t
| - Remove the spinlock
Since the spinlock seems to be only used to protect 'write_urb_busy', I agree
with those changes.
Greg, do you? If so, I suggested we should add the semaphore first, because
it is a bug fix.
I can do the 'write_urb_busy' type replace next week (yes, I will replace all
the drivers).
--
Luiz Fernando N. Capitulino
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