linux-kernel - Re: [PATCH 1/2] clk: mvebu: armada 370/XP add clock gating control provider for DT

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Message-ID: <20121119164611.2e754b64@skate>
Date:	Mon, 19 Nov 2012 16:46:11 +0100
From:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>
To:	Andrew Lunn <andrew@...n.ch>
Cc:	Gregory CLEMENT <gregory.clement@...e-electrons.com>,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 1/2] clk: mvebu: armada 370/XP add clock gating control
 provider for DT

Dear Andrew Lunn,

On Sat, 17 Nov 2012 14:54:35 +0100, Andrew Lunn wrote:
> > > What is the ddr clock for? Does bad things happen if you turn it off?
> > > Kirkwood has a similar clock, dunit, which i decided not to export,
> > > since when you turn it off, the whole SoC locks up.
> > 
> > Well of course if you code run in DDR then it could be a problem. But
> > I think it could be useful to turn it off when going to suspend, it
> > the DDR can do self-refresh. In this case it should be possible to run
> > the code from SRAM or L2 Cache.
> 
> O.K. Just watch out for the lateinit call in the clock framework.

I don't think there is a problem with the dramclk and the lateinit call
of the clock framework. The dramclk is a fixed factor clock, and the
fixed factor clock driver does not implement the ->disable() operation.
And therefore, the clk_disable_unused() code executed as the lateinit
call will not be able to disable it:

	if (__clk_is_enabled(clk) && clk->ops->disable)
		clk->ops->disable(clk->hw);

So I think we're quite safe with fixed rate clocks and fixed factor
clocks in that no-one can disable them :-)

Best regards,

Thomas
-- 
Thomas Petazzoni, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com
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