linux-kernel - Re: [v2 1/4] ARM: tegra20: create a DT header defining CLK IDs

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Message-ID: <20130221122536.GJ23234@tbergstrom-lnx.Nvidia.com>
Date:	Thu, 21 Feb 2013 14:25:36 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Hiroshi Doyu <hdoyu@...dia.com>,
	Russell King <linux@....linux.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <rob.herring@...xeda.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [v2 1/4] ARM: tegra20: create a DT header defining CLK IDs

On Fri, Feb 15, 2013 at 05:45:45PM +0100, Stephen Warren wrote:

...

> > I would suggest removing this clock. It's not actually implemented in the CCF
> > and rather useless. If you would gate the CPU clock from the CPU by writing to
> > this register, how would you ungate it? :) Note that this would gate the clock
> > to all CPUs.
> 
> (Note that my comment was re: all clocks, not just that one clock)
> 
> Can't the PMC or flow-controller ungate the clock based on some event?

I don't think the flow-controller controls this gate. The usual way of
clockgating a core is to execute a WFI instruction. That will trigger
clockgating the core, unless the flow-controller has been programmed to do
something else. The flow-controller will ungate the clock when there is an
interrupt.

> Either way, that clock definition exists in HW, right? So I don't think
> there's actually any harm in including the definition in the binding
> even if we never implement/use it.

The clock definition seems to exist in HW yes, the corresponding resetbit
however is marked as 'reserved' in the Tegra114 documentation.

Cheers,

Peter.
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