Re: [uclinux-dist-devel] [PATCH] serial: bfin_5xx: split uart RX lock from uart port lock to avoid deadlock

[Mike Frysinger <vapier@gentoo.org>]

On Thu, Feb 3, 2011 at 13:32, Greg KH wrote:
> On Thu, Feb 03, 2011 at 01:29:08AM -0500, Mike Frysinger wrote:
>> On Tue, Jan 11, 2011 at 00:16, Mike Frysinger wrote:
>> > From: Sonic Zhang <sonic.zhang@analog.com>
>> >
>> > The RX lock is used to protect the RX buffer from concurrent access in DMA
>> > mode between the timer and RX interrupt routines.  It is independent from
>> > the uart lock which is used to protect the TX buffer.  It is possible for
>> > a uart TX transfer to be started up from the RX interrupt handler if low
>> > latency is enabled.  So we need to split the locks to avoid deadlocking in
>> > this situation.
>> >
>> > In PIO mode, the RX lock is not necessary because the handle_simple_irq
>> > and handle_level_irq functions ensure driver interrupt handlers are called
>> > once on one core.
>> >
>> > And now that the RX path has its own lock, the TX interrupt has nothing to
>> > do with the RX path, so disabling it at the same time.
>>
>> ping ...
>
> Is this needed for .38?

it fixes a possible deadlock that exists in current .38 rc, but i
wouldnt call it a "critical" fix as it only affects certain edge
cases.  so if you want to merge for .38 or .39, either is OK for us i
think.
-mike
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