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

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Message-ID: <20181128102550.qsipssx67y3uexsr@flea>
Date:   Wed, 28 Nov 2018 11:25:50 +0100
From:   Maxime Ripard <maxime.ripard@...tlin.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        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

On Wed, Nov 28, 2018 at 05:30:07PM +0800, Chen-Yu Tsai wrote:
> 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: Maxime Ripard <maxime.ripard@...tlin.com>

Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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