linux-kernel - Re: [PATCH 04/15] dt-bindings: rtc: sun6i-rtc: Export internal RC oscillator

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Date:   Wed, 28 Nov 2018 19:18:26 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     alexandre.belloni@...tlin.com,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Mike Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-rtc@...r.kernel.org, linux-clk <linux-clk@...r.kernel.org>,
        devicetree <devicetree@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi@...glegroups.com
Subject: Re: [PATCH 04/15] dt-bindings: rtc: sun6i-rtc: Export internal RC oscillator

On Wed, Nov 28, 2018 at 6:33 PM Maxime Ripard <maxime.ripard@...tlin.com> wrote:
>
> On Wed, Nov 28, 2018 at 05:30:01PM +0800, Chen-Yu Tsai wrote:
> > Experiments showed that on at least the H3/H5/A64 the RTC's internal
> > oscillator also feeds the CPUS mux in the PRCM.
> >
> > Export this clock through the device tree, instead of having to use
> > a dummy fixed-clock device node, for the PRCM to consume. This will
> > properly describe the relationship between the clocks.
> >
> > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > ---
> >  Documentation/devicetree/bindings/rtc/sun6i-rtc.txt | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/Documentation/devicetree/bindings/rtc/sun6i-rtc.txt b/Documentation/devicetree/bindings/rtc/sun6i-rtc.txt
> > index 78c4fb472eb7..1bd37faadecb 100644
> > --- a/Documentation/devicetree/bindings/rtc/sun6i-rtc.txt
> > +++ b/Documentation/devicetree/bindings/rtc/sun6i-rtc.txt
> > @@ -24,7 +24,7 @@ Required properties:
> >
> >  Required properties for new device trees
> >  - clocks     : phandle to the 32kHz external oscillator
> > -- clock-output-names : names of the two clock outputs. See below.
> > +- clock-output-names : names of the three clock outputs. See below.
> >  - #clock-cells  : must be equal to 1.
> >
> >  The RTC provides the following clocks at the given indices:
> > @@ -32,6 +32,7 @@ The RTC provides the following clocks at the given indices:
> >  - 1: LOSC external output, known as X32KFOUT in the datasheet.
> >       This clock is not available on the A31 and is deprecated for old
> >       device trees still using the "allwinner,sun6i-a31-rtc" compatible.
> > +- 2: InternalOSC, or internal RC oscillator
>
> It seems to be required only for a few RTC though (H3, H5 and R40?)

IMO there's no harm in exporting it for all SoCs. I still don't know
if it's needed for the A31 either. And we don't have documents for the
PRCM stuff for any of the SoCs involved.

ChenYu