Re: [linux-usb-devel] Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t.

[Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>]

On Tue, 6 Dec 2005 23:36:47 +0100
Oliver Neukum <oliver@neukum.org> wrote:

| Am Dienstag, 6. Dezember 2005 22:18 schrieb Luiz Fernando Capitulino:
| > 
| >  Hi Pete,
| > 
| > On Tue, 6 Dec 2005 13:02:07 -0800
| > Pete Zaitcev <zaitcev@redhat.com> wrote:
| > 
| > | On Tue, 6 Dec 2005 18:14:49 -0200, Luiz Fernando Capitulino <lcapitulino@mandriva.com.br> wrote:
| > | 
| > | >  The spinlock makes the code less clear, error prone, and we already a
| > | > semaphore in the struct usb_serial_port.
| > | > 
| > | >  The spinlocks _seems_ useless to me.
| > | 
| > | Dude, semaphores are not compatible with interrupts. Surely you
| > | understand that?
| > 
| >  Sure thing man, take a look at this thread:
| > 
| > http://marc.theaimsgroup.com/?l=linux-kernel&m=113216151918308&w=2
| > 
| >  My comment 'we already have a semaphore in struct usb_serial_port'
| > was about what we've discussed in that thread, where question like
| > 'why should we have yet another lock here?' have been made.
| > 
| >  And *not* 'let's use the semaphore instead'.
| > 
| >  If _speed_ does not make difference, the spinlock seems useless,
| > because we could use atomic_t instead.
| 
| You can atomically set _one_ value using atomic_t. A spinlock allows
| that and other more complex schemes.

 We only need to set 'write_urb_busy', nothing more.

-- 
Luiz Fernando N. Capitulino
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