linux-kernel - Re: [PATCH v5 4/4] clk: dt: Introduce binding for always-on clock support

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Message-ID: <CAMuHMdXbWTuQAP9hg1qVCgaodkD3Wjin9UX=7uT=F0yodqEm+g@mail.gmail.com>
Date:	Thu, 2 Apr 2015 20:46:58 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Lee Jones <lee.jones@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	kernel@...inux.com, Mike Turquette <mturquette@...aro.org>,
	Stephen Boyd <sboyd@...eaurora.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v5 4/4] clk: dt: Introduce binding for always-on clock support

On Wed, Apr 1, 2015 at 2:28 PM, Lee Jones <lee.jones@...aro.org> wrote:
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>  .../devicetree/bindings/clock/clock-bindings.txt   | 31 ++++++++++++++++++++++
>  1 file changed, 31 insertions(+)
>
> diff --git a/Documentation/devicetree/bindings/clock/clock-bindings.txt b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> index 06fc6d5..94cdda2 100644
> --- a/Documentation/devicetree/bindings/clock/clock-bindings.txt
> +++ b/Documentation/devicetree/bindings/clock/clock-bindings.txt
> @@ -44,6 +44,37 @@ For example:
>    clocks by index. The names should reflect the clock output signal
>    names for the device.
>
> +clock-always-on:    Some hardware contains bunches of clocks which must never be
> +                   turned off.  If drivers a) fail to obtain a reference to any
> +                   of these or b) give up a previously obtained reference
> +                   during suspend, the common clk framework will attempt to
> +                   disable them and a platform can fail irrecoverably as a
> +                   result.  Usually the only way to recover from these failures
> +                   is to reboot.
> +
> +                   To avoid either of these two scenarios from catastrophically
> +                   disabling an otherwise perfectly healthy running system,
> +                   clocks can be identified as always-on using this property
> +                   from inside a clocksource's node.
> +
> +                   This property is not to be abused.  It is only to be used to
> +                   protect platforms from being crippled by gated clocks, not
> +                   as a convenience function to avoid using the framework
> +                   correctly inside device drivers.

Please document what are the expected value(s) for this property.
I assume these are clock indices into the array of hardware clocks?

Do they take into account sparse hardware clocks, cfr. the "clock-indices"
property below (I didn't check)?

> +For example:
> +
> +    oscillator {
> +        #clock-cells = <1>;
> +        clock-output-names = "ckil", "ckih";
> +        clock-always-on = <0>, <1>;
> +    };
> +
> +- this node defines a device with two clock outputs, just as in the
> +  example above.  The only difference being that 'ckil' and 'ckih'
> +  are now identified as an always-on clocks, so the framework will
> +  know to never attempt to gate them.
> +
>  clock-indices:    If the identifying number for the clocks in the node
>                    is not linear from zero, then this allows the mapping of
>                    identifiers into the clock-output-names array.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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