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

[Chen-Yu Tsai <wens@csie.org>]

On Mon, Aug 5, 2019 at 6:45 PM Ondřej Jirman <megous@megous.com> 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@googlegroups.com> wrote:
> > >
> > > From: Ondrej Jirman <megous@megous.com>
> > >
> > > 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@megous.com>
> > > ---
> > >  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

> 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?

> 3) configure gain on the LOSC
>
> regards,
>         o.
>
> > ChenYu
>
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