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

[Chen-Yu Tsai]

On Mon, Aug 5, 2019 at 7:10 PM OndÅej Jirman <megous@xxxxxxxxxx> wrote:
>
> On Mon, Aug 05, 2019 at 06:54:17PM +0800, Chen-Yu Tsai wrote:
> > On Mon, Aug 5, 2019 at 6:45 PM OndÅej Jirman <megous@xxxxxxxxxx> wrote:
> > >
> > > On Mon, Aug 05, 2019 at 06:16:14PM +0800, Chen-Yu Tsai wrote:
> > > > On Fri, Apr 12, 2019 at 8:07 PM megous via linux-sunxi
> > > > <linux-sunxi@xxxxxxxxxxxxxxxx> wrote:
> > > > >
> > > > > From: Ondrej Jirman <megous@xxxxxxxxxx>
> > > > >
> > > > > RTC on H6 is mostly the same as on H5 and H3. It has slight differences
> > > > > mostly in features that are not yet supported by this driver.
> > > > >
> > > > > Some differences are already stated in the comments in existing code.
> > > > > One other difference is that H6 has extra bit in LOSC_CTRL_REG, called
> > > > > EXT_LOSC_EN to enable/disable external low speed crystal oscillator.
> > > > >
> > > > > It also has bit EXT_LOSC_STA in LOSC_AUTO_SWT_STA_REG, to check whether
> > > > > external low speed oscillator is working correctly.
> > > > >
> > > > > This patch adds support for enabling LOSC when necessary:
> > > > >
> > > > > - during reparenting
> > > > > - when probing the clock
> > > > >
> > > > > H6 also has capacbility to automatically reparent RTC clock from
> > > > > external crystal oscillator, to internal RC oscillator, if external
> > > > > oscillator fails. This is enabled by default. Disable it during
> > > > > probe.
> > > > >
> > > > > Signed-off-by: Ondrej Jirman <megous@xxxxxxxxxx>
> > > > > ---
> > > > >  drivers/rtc/rtc-sun6i.c | 40 ++++++++++++++++++++++++++++++++++++++--
> > > > >  1 file changed, 38 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
> > > > > index 11f56de52179..7375a530c565 100644
> > > > > --- a/drivers/rtc/rtc-sun6i.c
> > > > > +++ b/drivers/rtc/rtc-sun6i.c
> > > > > @@ -41,9 +41,11 @@
> > > > >  /* Control register */
> > > > >  #define SUN6I_LOSC_CTRL                                0x0000
> > > > >  #define SUN6I_LOSC_CTRL_KEY                    (0x16aa << 16)
> > > > > +#define SUN6I_LOSC_CTRL_AUTO_SWT_BYPASS                BIT(15)
> > > >
> > > > Manual says bit 14? Or is this different from LOSC_AUTO_SWT_EN?
> > > >
> > > > The rest looks ok.
> > >
> > > To give you more information. This is a new thing in H6 BSP, compared
> > > to BSPs for previous SoCs (H5/H3).
> > >
> > >  20 #define REG_CLK32K_AUTO_SWT_EN                  BIT(14)
> > >  21 #define REG_CLK32K_AUTO_SWT_BYPASS              BIT(15)
> > >
> > > Init sequence changed in H6 BSP to:
> > >
> > > 646         /*
> > > 647          * Step1: select RTC clock source
> > > 648          */
> > > 649         tmp_data = readl(chip->base + SUNXI_LOSC_CTRL);
> > > 650         tmp_data &= (~REG_CLK32K_AUTO_SWT_EN);
> > > 651
> > > 652         /* Disable auto switch function */
> > > 653         tmp_data |= REG_CLK32K_AUTO_SWT_BYPASS;
> > > 654         writel(tmp_data, chip->base + SUNXI_LOSC_CTRL);
> > > 655
> > > 656         tmp_data = readl(chip->base + SUNXI_LOSC_CTRL);
> > > 657         tmp_data |= (RTC_SOURCE_EXTERNAL | REG_LOSCCTRL_MAGIC);
> > > 658         writel(tmp_data, chip->base + SUNXI_LOSC_CTRL);
> > > 659
> > > 660         /* We need to set GSM after change clock source */
> > > 661         udelay(10);
> > > 662         tmp_data = readl(chip->base + SUNXI_LOSC_CTRL);
> > > 663         tmp_data |= (EXT_LOSC_GSM | REG_LOSCCTRL_MAGIC);
> > > 664         writel(tmp_data, chip->base + SUNXI_LOSC_CTRL);
> > > 665
> >
> > I don't have this in my H6 BSPs. One is H6 Lichee v1.1 downloaded from Pine64.
> > The link was from linux-sunxi wiki's H6 page.
> >
> > The other is a 4.9 kernel tree, which I believe is from Allwinner's github:
> >
> >     https://github.com/Allwinner-Homlet/H6-BSP4.9-linux
>
> 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:
>
> 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. :)

That's good enough for me. I suppose if we do have any more doubts we could
ask them directly.


Reviewed-by: Chen-Yu Tsai <wens@xxxxxxxx>

> > > 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.

It's probably for the clock waveform to stabilize. Why they do it _after_
switching to the clock is weird though.

> regards,
>         o.
>
> >
> > > 3) configure gain on the LOSC
> > >
> > > regards,
> > >         o.
> > >
> > > > ChenYu
> > >
> > > --
> > > You received this message because you are subscribed to the Google Groups "linux-sunxi" group.
> > > To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscribe@xxxxxxxxxxxxxxxxx
> > > To view this discussion on the web, visit https://groups.google.com/d/msgid/linux-sunxi/20190805104529.z3mex3m2tss7lzlr%40core.my.home.
>
> --
> You received this message because you are subscribed to the Google Groups "linux-sunxi" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscribe@xxxxxxxxxxxxxxxxx
> To view this discussion on the web, visit https://groups.google.com/d/msgid/linux-sunxi/20190805111037.76vmanzcurffpbdf%40core.my.home.