linux-kernel - Re: [linux-sunxi] [PATCH 2/3] rtc: sun6i: Add support for H6 RTC

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Date:   Mon, 5 Aug 2019 14:16:29 +0200
From:   Clément Péron <peron.clem@...il.com>
To:     megous@...ous.com, Chen-Yu Tsai <wens@...e.org>,
        Alessandro Zummo <a.zummo@...ertech.it>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Maxime Ripard <maxime.ripard@...tlin.com>,
        linux-rtc@...r.kernel.org, devicetree <devicetree@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        linux-sunxi <linux-sunxi@...glegroups.com>
Subject: Re: [linux-sunxi] [PATCH 2/3] rtc: sun6i: Add support for H6 RTC

Hi,

On Mon, 5 Aug 2019 at 13:10, Ondřej Jirman <megous@...ous.com> wrote:
>
> On Mon, Aug 05, 2019 at 06:54:17PM +0800, Chen-Yu Tsai wrote:
> > On Mon, Aug 5, 2019 at 6:45 PM Ondřej Jirman <megous@...ous.com> wrote:
> > >
[snip]
>
> Interesting. :) I have the BSP I was using saved here:
>
> https://megous.com/git/linux/tree/drivers/rtc/rtc-sunxi.c?h=h6-4.9-bsp#n649
>
> It's based of 4.9.119
>
> https://megous.com/git/linux/log/?h=h6-4.9-bsp
>
> I don't remember where I found it. But I imported it fairly recently, and
> the code you pointed to looks like an older version that I can found in some
> beta H6 BSP, that I imported way earlier and is based on 4.9.56:

The last recent that I know is from OrangePi H6 but it's based on 4.9.118.

https://github.com/orangepi-xunlong/OrangePiH6_Linux4_9

Regards,
Clément

>
> https://megous.com/git/linux/tree/drivers/rtc/rtc-sunxi.c?h=linux-h6
> https://megous.com/git/linux/log/?h=linux-h6
>
> Hmm, archeology. :)
>
> > > For older BSPs, the init sequence looked like this:
> > >
> > > 482         /*
> > > 483          * Step1: select RTC clock source
> > > 484          */
> > > 485         tmp_data = sunxi_rtc_read(SUNXI_LOSC_CTRL_REG);
> > > 486         tmp_data &= (~REG_CLK32K_AUTO_SWT_EN);
> > > 487         tmp_data |= (RTC_SOURCE_EXTERNAL | REG_LOSCCTRL_MAGIC);
> > > 488         tmp_data |= (EXT_LOSC_GSM);
> > > 489         sunxi_rtc_write(tmp_data, SUNXI_LOSC_CTRL_REG);
> > > 490
> > >
> > > EXT_LOSC_GSM has values 4 values from low to high, and I guess it configures
> > > gain for the oscillator's amplifier in the feedback loop of the circuit.
> > >
> > > So the new code, for some reason changed from single write to sequence
> > > of individual writes/config steps:
> > >
> > > 1) disable auto-switch and enable auto-switch bypass
> > > 2) select RTC clock source (to LOSC)
> > >   (wait)
> >
> > Maybe it's possible to glitch if these two are combined?
>
> That's what I thought too. Or the programmer thought so, and was just
> programming defensively, and there's no real problem in the practice.
>
> But that specific delay() seems like someone trying to solve a real issue. Of
> course there's no knowing if it was on H6 or on some other SoC.
>
> regards,
>         o.
>
> >
> > > 3) configure gain on the LOSC
> > >
> > > regards,
> > >         o.
> > >
> > > > ChenYu
> > >
> > > --
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>
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