Date: Tue, 6 Dec 2005 09:56:10 -0200
From: Luiz Fernando Capitulino <lcapitulino@mandriva.com.br>
To: gregkh@suse.de
Cc: linux-kernel@vger.kernel.org, linux-usb-devel@lists.sourceforge.net,
       ehabkost@mandriva.com
Subject: [PATCH 00/10] usb-serial: Switches from spin lock to atomic_t.
Message-Id: <20051206095610.29def5e7.lcapitulino@mandriva.com.br>
Organization: Mandriva
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 Greg,

 Don't get scared. :-)

 As showed by Eduardo Habkost some days ago, the spin lock 'lock' in the
struct 'usb_serial_port' is being used by some USB serial drivers to protect
the access to the 'write_urb_busy' member of the same struct.

 The spin lock however, is needless: we can change 'write_urb_busy' type
to be atomic_t and remove all the spin lock usage.

 The following patch series does that. It introduces a very simple URB write
lock abstraction and four macros to do the same job currently done by the
spin lock.

 The final result is a simpler and easy to read/understand code, with no
spin lock at all.

 I've splited the work that way: the frist patch introduces the new macros;
from the second patch until the eight all the drivers are ported; patch
nine removes the 'lock' member from the usb-serial driver and patch ten
adds the write URB lock initialization for all the ports.

 An important note is about the omninet driver. In its omninet_write_room()
method, it's accessing the 'write_urb_busy' member from the 'serial->port[1]'
port, and _not_ from the usb_serial_port passed as its argument. I have no
sure if it is right, but my port does perserve that semantic.

 As I don't have any of the changed drivers, I have only made the compilation
test. Would be good to hold the patches in -mm for a while.

 A final note: all the patches have been made with my usb-serial fixes
(which are already in your tree) applyed. They are:

usbserial-adds-missing-checks-and-bug-fix.patch
usbserial-race-condition-fix.patch

 Thank you,

-- 
Luiz Fernando N. Capitulino
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