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

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Message-ID: <CAJe_Zhf=GBb8AfnTLaGxGcZkVSm9TtdnTsmpH_MBmbMT8ViMDg@mail.gmail.com>
Date:	Sat, 28 Feb 2015 14:51:17 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Lee Jones <lee.jones@...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 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.
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?

-Jassi
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