Re: [PATCH 2/3] clk: qcom: Elaborate on "active" clocks in the RPM clock bindings

[Stephen Boyd <sboyd-sgV2jX0FEOL9JmXXK+q4OQ@public.gmane.org>]

On 03/29, Linus Walleij wrote:
> On Wed, Mar 29, 2017 at 2:59 AM, Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> > On Wed, Mar 22, 2017 at 09:18:42AM +0100, Linus Walleij wrote:
> >> The concept of "active" clocks is just explained in a bried comment in the
> >> device driver, let's explain it a bit more in the device tree bindings
> >> so everyone understands this.
> >>
> >> Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> >> Signed-off-by: Linus Walleij <linus.walleij-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> >> ---
> >>  Documentation/devicetree/bindings/clock/qcom,rpmcc.txt | 8 ++++++++
> >>  1 file changed, 8 insertions(+)
> >>
> >> diff --git a/Documentation/devicetree/bindings/clock/qcom,rpmcc.txt b/Documentation/devicetree/bindings/clock/qcom,rpmcc.txt
> >> index d470a0187035..cf80a00b7ff2 100644
> >> --- a/Documentation/devicetree/bindings/clock/qcom,rpmcc.txt
> >> +++ b/Documentation/devicetree/bindings/clock/qcom,rpmcc.txt
> >> @@ -18,6 +18,14 @@ Required properties :
> >>
> >>  - #clock-cells : shall contain 1
> >>
> >> +The clock enumerators are defined in <dt-bindings/clock/qcom,rpmcc.h>
> >> +and come in pairs: FOO_CLK followed by FOO_A_CLK. The latter clock
> >> +is an "active" clock, which means that the consumer only care that the
> >> +clock is available when the system is active, i.e. not suspended. If

I would further say that "is available when the apps CPU
subsystem is active", i.e. not suspended or in deep idle. Really
it's about optimizing the idle path so we don't have to keep
things on for the CPU when it powers down. The system suspend
case can usually be handled by regular clk API calls.

> >> +it is important that the clock keeps running during system suspend,
> >> +you need to specify the non-active clock, the one not containing
> >> +*_A_* in the enumerator name.
> >> +
> >
> > Sounds like abuse as the clock id is encoding policy into it. The number
> > of clocks should be the number of inputs to a block. I wouldn't be
> > opposed to some flags for clocks, but that should be a separate cell.
> 
> I'm sorry about that, but I'm just documenting what is already a fact and
> was previously just implicit in the name.
> 
> I first had no idea what this *_A_* infix notation was about so after some
> reading I found a comment in the driver saying this.
> 
> I guess Stephen can confirm and/or elaborate on this.
> 
> Keeping them around is I guess the lesser evil (as compard to
> pulling up the deployed bindings with the roots) at this point.
> 

Yes we can't really do much now that we've put the binding out
there. I guess we could have two cells and then fold that into a
custom clk_hw getter function to map the two cells to the right
clk. And then leave the original code around for backwards compat
and detect which one to register as the clk_hw provider.

Either way, that wouldn't change the consumer binding because if
they want to control the *_A_* and non *_A_* clks as individual
controls they'll list the same physical clk twice in their
'clocks' property.

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