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

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Date:   Wed, 28 Nov 2018 13:29:04 -0800
From:   Stephen Boyd <sboyd@...nel.org>
To:     Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Chen-Yu Tsai <wens@...e.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        Michael Turquette <mturquette@...libre.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     Chen-Yu Tsai <wens@...e.org>, linux-arm-kernel@...ts.infradead.org,
        linux-rtc@...r.kernel.org, linux-clk@...r.kernel.org,
        devicetree@...r.kernel.org, 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

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>