From: Oliver Neukum <oliver@neukum.org>
To: linux-usb-devel@lists.sourceforge.net
Subject: Re: [linux-usb-devel] Re: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t.
Date: Tue, 6 Dec 2005 23:36:47 +0100
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Cc: Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>,
       Pete Zaitcev <zaitcev@redhat.com>, gregkh@suse.de,
       linux-kernel@vger.kernel.org, ehabkost@mandriva.com
References: <20051206095610.29def5e7.lcapitulino@mandriva.com.br> <20051206130207.7658636e.zaitcev@redhat.com> <20051206191845.6f4827b3.lcapitulino@mandriva.com.br>
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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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