Re: [linux-sunxi] [PATCH 2/3] rtc: sun6i: Add support for H6 RTC
From: Chen-Yu Tsai
Date: Mon Aug 05 2019 - 06:54:36 EST
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);
> 652 /* Disable auto switch function */
> 653 tmp_data |= REG_CLK32K_AUTO_SWT_BYPASS;
> 654 writel(tmp_data, chip->base + SUNXI_LOSC_CTRL);
> 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);
> 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);
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:
> 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);
> 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)
Maybe it's possible to glitch if these two are combined?
> 3) configure gain on the LOSC
> > ChenYu
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