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

    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. :)

    > > 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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