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SubjectRe: [linux-sunxi] [PATCH v2 2/3] rtc: sun6i: Add support for H6 RTC
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Dne sobota, 24. avgust 2019 ob 23:27:46 CEST je Ondřej Jirman napisal(a):
> Hello Jernej,
>
> On Sat, Aug 24, 2019 at 11:09:49PM +0200, Jernej Škrabec wrote:
> > > Visually?
> > >
> > > That would explain why it doesn't work for you. The mainline RTC driver
> > > disables auto-switch feature, and if your board doesn't have a crystal
> > > for
> > > LOSC, RTC will not generate a clock for the RTC.
> > >
> > > H6's dtsi describes by default a situatiuon with external 32k crystal
> > > oscillator. See ext_osc32k node. That's incorrect for your board if it
> > > doesn't have the crystal. You need to fix this in the DTS for your board
> > > instead of patching the driver.
> >
> > I see that reparenting is supported, but I'm not sure how to fix that in
> > DT. Any suggestion?
>
> You may try removing the clocks property from rtc node.

I don't think this would work:
https://elixir.bootlin.com/linux/latest/source/drivers/rtc/rtc-sun6i.c#L246

>
> > > The driver has parent clock selection logic in case the LOSC crystal is
> > > not
> > > used.
> > >
> > > Your patch enables automatic detection of LOSC failure and RTC changes
> > > clock to LOSC automatically, despite what's described in the DTS. That
> > > may fix the issue, but is not the correct solution.
> > >
> > > Registers on my board look like this (external 32k osc is used) for
> > > reference:
> > >
> > > LOSC_CTRL_REG[7000000]: 8011
> > >
> > > KEY_FIELD ??? (0)
> > > LOSC_AUTO_SWT_BYPASS EN (1)
> > > LOSC_AUTO_SWT_EN DIS (0)
> > > EXT_LOSC_EN EN (1)
> > > EXT_LOSC_GSM LOW (0)
> > > BATTERY_DIR DISCHARGE (0)
> > > LOSC_SRC_SEL EXT32k (1)
> > >
> > > LOSC_AUTO_SWT_STA_REG[7000004]: 1
> > >
> > > EXT_LOSC_STA OK (0)
> > > LOSC_AUTO_SWT_PEND NOEFF (0)
> > > LOSC_SRC_SEL_STA EXT32K (1)
> >
> > In my case LOSC_CTRL_REG has value 0x4010 and LOSC_AUTO_SWT_STA_REG
> > has value 0x4, so there is issue with external crystal (it's missing) and
> > RTC switched to internal one.
> >
> > BTW, what's wrong with automatic switching? Why is it disabled?
>
> It always was disabled on mainline (bit 14 was set to 0 even before my
> patch). H6 just probably has another extra undocummented bit, that's needed
> to disables it properly.
>
> You probably don't want a glitch to switch your RTC from high-precision
> clock to a low precision one possibly without any indication in the
> userspace or a kernel log.
>
> Regardless of all this, DTS needs to have a correct description of the HW,
> which means if RTC module is not connected to the 32.757kHz crystal/clock,
> clocks property should be empty.

If we are talking about correct HW description, then clock property should
actually have possibility that two clocks are defined - one for internal RC
(always present) and one external crystal (optional). In such case I could
really just omit external clock and be done with it. But I'm not sure if such
solution is acceptable at this point.

Best regards,
Jernej

>
> regards,
> o.
>
> > Best regards,
> > Jernej
> >
> > > regards,
> > >
> > > o.
> > >
> > > > > The real issue probably is that the mainline driver is missing this:
> > > > >
> > > > > https://megous.com/git/linux/tree/drivers/rtc/rtc-sunxi.c?h=h6-4.9-b
> > > > > sp#n
> > > > > 650
> > > >
> > > > Not sure what you mean by that. ext vs. int source selection?
> > > >
> > > >
> > > >
> > > > Best regards,
> > > > Jernej
> > > >
> > > > > regards,
> > > > >
> > > > > o.




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