[Query] Common Clock Framework: How to handle clks enabled by default

[Shawn Guo]

On 17 April 2012 14:21, Viresh Kumar <viresh.kumar at st.com> wrote:
> Hi,
>
> How are we handling clocks which are enabled by bootloaders and are
> required to be enabled, like, pll, cpu, ahb?
>
Call clk_prepare_enable on the clocks in platform clock init function.

> Following is example clk hierarchy:
> osc(root)->pll->cpu->ahb->dma
>
> Issue1: Now, when we do clk_enable() for dma, all these already enabled clocks
> are re-enabled.

What's the problem with doing that?  Your hardware does not cope with
setting/clearing a bit that already set/cleared.  Even if that is the
case, you can easily handle that in your .enable/.disable ops.

> Issue2: On clk_disable() all are disabled and system hangs :(
>
It should not.  It means you have other clocks in the hierarchy not
manged well.  The parent of the clock will not be gated by calling
clk_disable, if there are other sibling clocks are enabled.

> There is one option CLK_IGNORE_UNUSED, which is used only for disabling
> unused clocks. So that is not helpful here.
>
> One way i could think of is not to give clk_gate support for these clocks,
> so that they can never be disabled. Is this the preferred way?
>
It only makes sense on those completely internal clocks which will
never need managing.

Regards,
Shawn

> I can't guarantee, but these clocks might be required to be disabled
> for standby/sleep cases.
>