From: Jeremy Kerr <jeremy.kerr@canonical.com>
To: Saravana Kannan <skannan@codeaurora.org>
Subject: Re: [RFC,PATCH 2/3] clk: Generic support for fixed-rate clocks
Date: Tue, 15 Feb 2011 14:18:37 +0800
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Cc: linux-arm-kernel@lists.infradead.org,
        Nicolas Pitre <nicolas.pitre@linaro.org>,
        Lorenzo Pieralisi <Lorenzo.Pieralisi@arm.com>,
        Vincent Guittot <vincent.guittot@linaro.org>, linux-sh@vger.kernel.org,
        Ben Herrenschmidt <benh@kernel.crashing.org>,
        Sascha Hauer <s.hauer@pengutronix.de>,
        Paul Mundt <lethal@linux-sh.org>, linux-kernel@vger.kernel.org,
        Ryan Mallon <ryan@bluewatersys.com>, Dima Zavin <dmitriyz@google.com>,
        Ben Dooks <ben-linux@fluff.org>,
        "Uwe =?iso-8859-1?q?Kleine-K=F6nig?=" 
	<u.kleine-koenig@pengutronix.de>,
        Russell King <linux@arm.linux.org.uk>
References: <1297233693.242725.820672531799.2.gpush@pororo> <201102150941.00668.jeremy.kerr@canonical.com> <4D5A063F.1010102@codeaurora.org>
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Hi Saravana,

> >> A fixed clock may still have other operations such as enable/disable.
> > 
> > Then it's not a fixed clock; I'd prefer this to be a separate type, as
> > it's now hardware dependent.
> 
> I'm confused. If a clock's rate can't be changed and it can't be enabled
> or disabled, then what's the point of representing that clock
> signal/line as a clock in the driver.

Because the drivers using this clock don't know that it's a fixed clock.

For example, a uart needs to know the rate of its clock source, so that it can 
set its internal divisors to get a valid baud rate. The uart driver will query  
the input rate using clk_get_rate(). The driver still needs to call 
clk_enable/clk_prepare/etc, because on some systems it may have a switchable 
clock.

Cheers,


Jeremy

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