linux-kernel - Re: [linux-sunxi] [PATCH 0/3] Add basic support for RTC on Allwinner H6 SoC

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Date:   Thu, 8 Aug 2019 13:48:55 +0800
From:   Chen-Yu Tsai <wens@...e.org>
To:     Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        devicetree <devicetree@...r.kernel.org>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-rtc@...r.kernel.org
Subject: Re: [linux-sunxi] [PATCH 0/3] Add basic support for RTC on Allwinner
 H6 SoC

On Wed, Aug 7, 2019 at 6:55 PM Alexandre Belloni
<alexandre.belloni@...tlin.com> wrote:
>
> Hi,
>
> On 06/08/2019 20:30:45+0200, Ondřej Jirman wrote:
> > Maybe whether XO or DCXO is used also matters if you want to do some fine
> > tunning of DCXO (control register has pletny of options), but that's probably
> > better done in u-boot. And there's still no need to read HOSC source from DT.
> > The driver can just check compatible, and if it is H6 and OSC_CLK_SRC_SEL is 1,
> > it can do it's DCXO tunning, or whatever. But neither OS nor bootloader will
> > be using this info to gate/disable the osciallator.
> >
>
> It is actually useful to be able to tweak the crystal tuning at
> runtime to be able to reduce clock drift and compare with a reliable
> source (e.g. NTP).
> I'm curious, what kind of options does this RTC have?

It has options to set the current, trim cap value, band gap voltage, and also
change the mode to just accept an external clock signal, instead of driving
a crystal. The settings for the former parameters are not explained though.

See page 364 of
http://linux-sunxi.org/File:Allwinner_H6_V200_User_Manual_V1.1.pdf

ChenYu