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

Geert Uytterhoeven
2015-04-02T18:47:05Z

On Wed, Apr 1, 2015 at 2:28 PM, Lee Jones <lee.jones@linaro.org> wrote:
> Signed-off-by: Lee Jones <lee.jones@linaro.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@linux-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