Re: [PATCH v7 0/5] clk: Provide support for always-on clocks

Michael Turquette
2015-07-30T00:27:40Z

Quoting Lee Jones (2015-07-22 06:04:10)
> 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 provider is registered with the
> framework it is possible for a list of critical clocks to be supplied
> which must be kept ungated. Each clock mentioned in the newly
> introduced 'critical-clock' property will be clk_prepare_enable()d
> where the normal references will be taken. This will prevent the
> common clk framework from attempting to gate them during the normal
> clk_disable_unused() and disable_clock() procedures.
>
> Note that it will still be possible for knowledgeable drivers to turn
> these clocks off using clk_{enable,disable}_critical() calls.

Hi Lee,

Thanks for submitting the series.

It has been a little while since v6. It would be helpful to remind me of
why a new api is necessary, versus using the existing clk_prepare_unused
call at the time that a clock is enabled.

I'm looking over the patches in detail now, but one question stands out:
besides the DT use case, would a Linux device driver ever call
clk_enable_critical instead of using clk_enable? If so, why?

Thanks,
Mike

>
> Changelog:
> v6 => v7:
> - Introduce API to enable and disable critical clocks
> - Rename 'always-on-clock' to 'critical-clock'
>
> v5 => v6:
> - Use of_clk_get_from_provider() instead of of_clk_get_by_clkspec()
> - Explicitly describe expected DT values
> - Be pedantic with regards to printk() format specifiers
>
> vX => v5:
> Implementations have changed drastically between versions, thus I
> would like for this set to be thought of independently from its
> predecessors. The only reason for identifying as 'v5' is ease of
> differentiation on the list, which stems from the confusion caused
> by submitting 'v4' as a separate entity.
>
> Lee Jones (5):
> ARM: sti: stih407-family: Supply defines for CLOCKGEN A0
> ARM: sti: stih410-clocks: Identify critical clocks
> clk: Supply the critical clock {init, enable, disable} framework
> clk: Provide critical clock support
> clk: dt: Introduce binding for critical clock support
>
> .../devicetree/bindings/clock/clock-bindings.txt | 39 +++++++++++++++++++
> arch/arm/boot/dts/stih410-clock.dtsi | 10 +++++
> drivers/clk/clk-conf.c | 45 +++++++++++++++++++++-
> drivers/clk/clk.c | 45 ++++++++++++++++++++++
> include/dt-bindings/clock/stih407-clks.h | 4 ++
> include/linux/clk-provider.h | 2 +
> include/linux/clk.h | 30 +++++++++++++++
> 7 files changed, 174 insertions(+), 1 deletion(-)
>
> --
> 1.9.1
>