linux-kernel - Re: [PATCH 09/15] clk: sunxi-ng: r40: Force LOSC parent to RTC LOSC output

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Message-ID: <CAGb2v64cER=qU2e_jnZemVfYbtQFNk+ev1MFBQDQu86f98X2dw@mail.gmail.com>
Date:   Fri, 30 Nov 2018 11:55:44 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Maxime Ripard <maxime.ripard@...tlin.com>
Cc:     Stephen Boyd <sboyd@...nel.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        alexandre.belloni@...tlin.com, Mark Rutland <mark.rutland@....com>,
        Mike Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>,
        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 09/15] clk: sunxi-ng: r40: Force LOSC parent to RTC LOSC output

On Thu, Nov 29, 2018 at 5:29 AM Stephen Boyd <sboyd@...nel.org> wrote:
>
> Quoting Chen-Yu Tsai (2018-11-28 01:30:07)
> > On the R40, in addition to a mux between the RTC's own RC oscillator and
> > an external 32768 Hz crystal, which are muxed inside the RTC module, the
> > CCU also has its own RC oscillator, which runs at around 2 MHz, and can
> > be muxed with the LOSC output from the RTC. This muxed output is called
> > "SYS 32K" in the module clock diagram, but otherwise referred to as the
> > LOSC throughout the CCU documentation.
> >
> > The RC oscillator is not very accurate, even though it has an undocumented
> > calibration function. We really want a precise clock at 32768 Hz,
> > instead of something at around 32 KHz. This patch forces the SYS 32K
> > clock to use the RTC output as its parent, and doesn't bother
> > registering the internal oscillator nor a clock mux.
> >
> > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > ---
>
> Acked-by: Stephen Boyd <sboyd@...nel.org>

Merged with acks from Maxime and Stephen.