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Date: Thu, 27 Jan 2011 12:30:36 -0800
From: Saravana Kannan <skannan@codeaurora.org>
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To: Russell King - ARM Linux <linux@arm.linux.org.uk>
CC: Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        linux-sh <linux-sh@vger.kernel.org>,
        Ben Herrenschmidt <benh@kernel.crashing.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
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Subject: Re: Locking in the clk API
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> <20110127085438.GA25239@n2100.arm.linux.org.uk>
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On 01/27/2011 12:54 AM, Russell King - ARM Linux wrote:
> 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.

For internal tree purposes, does .set_termios need to be atomic? Can it 
grab mutexes instead of spinlock?

Going back to the topic, how about CPU freq drivers possibly using 
clk_set_rate() to change freq? Do you think that's not the case or a 
concern?

All,

Do any one of your mach's control CPU freq using clk_set_rate() and does 
it need to be atomic? CPUfreq doesn't need it to be atomic. So, you will 
need clk_set_rate() to be atomic only if you try to use it to lower CPU 
freq very late during idle/suspend.

-Saravana

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