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

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Date:	Mon, 2 Mar 2015 15:38:12 +0530
From:	Jassi Brar <jassisinghbrar@...il.com>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	Jassi Brar <jaswinder.singh@...aro.org>,
	Devicetree List <devicetree@...r.kernel.org>,
	Mike Turquette <mturquette@...aro.org>, kernel@...inux.com,
	Stephen Boyd <sboyd@...eaurora.org>,
	lkml <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/4] clk: Provide always-on clock support

On Mon, Mar 2, 2015 at 2:06 PM, Lee Jones <lee.jones@...aro.org> wrote:
> 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
>
Thanks, I wasn't aware of the history.

>> 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?
>
The phantom user - that's there but none can see it.

How about?

+       of_property_for_each_string(np, "clock-always-on", prop, clkname) {
+               clk = __clk_lookup(clkname);
+               if (!clk)
+                       continue;
+
+               clk->core->enable_count = 1;
+               clk->core->prepare_count = 1;
+       }

-jassi
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