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To:     Alessandro Zummo <a.zummo@towertech.it>,
        Alexandre Belloni <alexandre.belloni@bootlin.com>,
        Chen-Yu Tsai <wens@csie.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Maxime Ripard <maxime.ripard@bootlin.com>,
        Michael Turquette <mturquette@baylibre.com>,
        Rob Herring <robh+dt@kernel.org>
From:   Stephen Boyd <sboyd@kernel.org>
In-Reply-To: <20181128093013.24442-11-wens@csie.org>
Cc:     Chen-Yu Tsai <wens@csie.org>, linux-arm-kernel@lists.infradead.org,
        linux-rtc@vger.kernel.org, linux-clk@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-sunxi@googlegroups.com
References: <20181128093013.24442-1-wens@csie.org>
 <20181128093013.24442-11-wens@csie.org>
Message-ID: <154344054442.88331.8887745218976145062@swboyd.mtv.corp.google.com>
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Subject: Re: [PATCH 09/15] clk: sunxi-ng: r40: Force LOSC parent to RTC LOSC output
Date:   Wed, 28 Nov 2018 13:29:04 -0800
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@csie.org>
> ---

Acked-by: Stephen Boyd <sboyd@kernel.org>