linux-kernel - Re: [PATCH 3/4] clk: Provide always-on clock support

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Date:	Mon, 2 Mar 2015 08:36:52 +0000
From:	Lee Jones <lee.jones@...aro.org>
To:	Jassi Brar <jaswinder.singh@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>, sboyd@...eaurora.org,
	kernel@...inux.com, Devicetree List <devicetree@...r.kernel.org>
Subject: Re: [PATCH 3/4] clk: Provide always-on clock support

On Sat, 28 Feb 2015, Jassi Brar wrote:

> On 28 February 2015 at 02:44, Lee Jones <lee.jones@...aro.org> wrote:
> > Lots of platforms contain clocks which if turned off would prove fatal.
> > The only way to recover from these catastrophic failures is to restart
> > the board(s).  Now, when a clock is registered with the framework it is
> > compared against a list of provided always-on clock names which must be
> > kept ungated.  If it matches, we enable the existing CLK_IGNORE_UNUSED
> > flag, which will prevent the common clk framework from attempting to
> > gate it during the clk_disable_unused() procedure.
> >
> If a clock is critical on a certain board, it could be got+enabled
> during early boot so there is always a user.

I tried this.  There was push-back from the DT maintainers.

  http://lists.infradead.org/pipermail/linux-arm-kernel/2015-February/324417.html

> To be able to do that from DT, maybe add a new, say, CLK_ALWAYS_ON
> flag could be made to initialize the clock with one phantom user
> already. Or just reuse the CLK_IGNORE_UNUSED?

How is that different to what this set is doing?

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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