From mboxrd@z Thu Jan  1 00:00:00 1970
From: Maxime Ripard <maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>
Subject: Re: [PATCH 09/15] clk: sunxi-ng: r40: Force LOSC parent
 to RTC LOSC output
Date: Wed, 28 Nov 2018 11:25:50 +0100
Message-ID: <20181128102550.qsipssx67y3uexsr@flea>
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To: Chen-Yu Tsai <wens-jdAy2FN1RRM@public.gmane.org>
Cc: Alexandre Belloni <alexandre.belloni-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>, Alessandro Zummo <a.zummo-BfzFCNDTiLLj+vYz1yj4TQ@public.gmane.org>, Michael Turquette <mturquette-rdvid1DuHRBWk0Htik3J/w@public.gmane.org>, Stephen Boyd <sboyd-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>, Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>, linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org, linux-rtc-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-clk-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-sunxi-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
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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-jdAy2FN1RRM@public.gmane.org>

Acked-by: Maxime Ripard <maxime.ripard-LDxbnhwyfcJBDgjK7y7TUQ@public.gmane.org>

Maxime

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