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

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Date:	Thu, 21 Feb 2013 17:32:40 +0200
From:	Peter De Schrijver <pdeschrijver@...dia.com>
To:	Stephen Warren <swarren@...dotorg.org>
CC:	Russell King <linux@....linux.org.uk>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"devicetree-discuss@...ts.ozlabs.org" 
	<devicetree-discuss@...ts.ozlabs.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>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Hiroshi Doyu <hdoyu@...dia.com>
Subject: Re: [v2 1/4] ARM: tegra20: create a DT header defining CLK IDs

On Thu, Feb 21, 2013 at 01:25:36PM +0100, Peter De Schrijver wrote:
> 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.

Apparently from Tegra114 onwards, this bit no longer exists. In previous
chips, it is just turned by the bootloader running on the AVP and stays on
from there on. So at least for Tegra114 I think we remove this clock from
the DT binding.

Cheers,

Peter.
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