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

Regards
Oliver
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