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Date: Thu, 27 Jan 2011 08:54:38 +0000
From: Russell King - ARM Linux <linux@arm.linux.org.uk>
To: Saravana Kannan <skannan@codeaurora.org>
Cc: Colin Cross <ccross@google.com>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-sh <linux-sh@vger.kernel.org>,
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	<u.kleine-koenig@pengutronix.de>,
        Jeremy Kerr <jeremy.kerr@canonical.com>,
        linux-arm-kernel <linux-arm-kernel@lists.infradead.org>,
        Richard Zhao <linuxzsc@gmail.com>
Subject: Re: Locking in the clk API
Message-ID: <20110127085438.GA25239@n2100.arm.linux.org.uk>
References: <201101111016.42819.jeremy.kerr@canonical.com> <20110111091607.GI12552@n2100.arm.linux.org.uk> <201101111744.59712.jeremy.kerr@canonical.com> <20110111103929.GN24920@pengutronix.de> <AANLkTinHL9X_bqMPR=W8Va01O4xngUnpGCkCiE3xEdiQ@mail.gmail.com> <4D386ABF.9060908@fluff.org> <20110120190822.GK6335@n2100.arm.linux.org.uk> <4D3932B4.8010904@codeaurora.org> <20110121094042.GD13235@n2100.arm.linux.org.uk> <4D40F5CC.6080809@codeaurora.org>
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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.