linux-kernel - Re: Locking in the clk API

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Message-ID: <20110127085438.GA25239@n2100.arm.linux.org.uk>
Date:	Thu, 27 Jan 2011 08:54:38 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Saravana Kannan <skannan@...eaurora.org>
Cc:	Colin Cross <ccross@...gle.com>,
	Lorenzo Pieralisi <Lorenzo.Pieralisi@....com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	linux-sh <linux-sh@...r.kernel.org>,
	Ben Herrenschmidt <benh@...nel.crashing.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Ben Dooks <ben-linux@...ff.org>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
	Richard Zhao <linuxzsc@...il.com>
Subject: Re: Locking in the clk API

On Wed, Jan 26, 2011 at 08:34:20PM -0800, Saravana Kannan wrote:
> I'm not too familiar with serial/tty, does anyone know if the  
> .set_termios needs to be atmoic? If not, we could just change  
> cpm_uart/cpm_uart_core.c to use mutex instead of spinlock.

The locking is there to protect against the interrupt handler accessing
the port->* stuff (which seems to have been forgotten by the cpm driver).

I don't see any reason why clk_set_rate() needs to be under the spinlock
there - we need the reprogramming of the baud rate within the spinlock
on 8250 because of DLAB bit hiding the data registers.  It's also a good
idea that it _is_ within the spinlock along with uart_update_timeout()
to ensure timeouts and the baud rate are updated together.
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