Re: [PATCH 1/2] rtc: sun6i: Make external 32k oscillator optional

From: "Jernej Škrabec" <jernej.skrabec@siol.net>
To: Maxime Ripard <maxime@cerno.tech>
Cc: mark.rutland@arm.com, a.zummo@towertech.it,
	alexandre.belloni@bootlin.com, devicetree@vger.kernel.org,
	linux-kernel@vger.kernel.org, wens@csie.org, robh+dt@kernel.org,
	linux-arm-kernel@lists.infradead.org, linux-rtc@vger.kernel.org
Subject: Re: [PATCH 1/2] rtc: sun6i: Make external 32k oscillator optional
Date: Fri, 14 Feb 2020 17:42:13 +0100	[thread overview]
Message-ID: <5326350.DvuYhMxLoT@jernej-laptop> (raw)
In-Reply-To: <20200214081443.ajz2sxh5ztk6qb2i@gilmour.lan>

Hi Maxime,

Dne petek, 14. februar 2020 ob 09:14:43 CET je Maxime Ripard napisal(a):
> Hi Jernej,
> 
> Thanks for taking care of this
> 
> On Thu, Feb 13, 2020 at 10:14:26PM +0100, Jernej Skrabec wrote:
> > Some boards, like OrangePi PC2 (H5), OrangePi Plus 2E (H3) and Tanix TX6
> > (H6) don't have external 32kHz oscillator. Till H6, it didn't really
> > matter if external oscillator was enabled because HW detected error and
> > fall back to internal one. H6 has same functionality but it's the first
> > SoC which have "auto switch bypass" bit documented and always enabled in
> > driver. This prevents RTC to work correctly if external crystal is not
> > present on board. There are other side effects - all peripherals which
> > depends on this clock also don't work (HDMI CEC for example).
> > 
> > Make clocks property optional. If it is present, select external
> > oscillator. If not, stay on internal.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
> > ---
> > 
> >  drivers/rtc/rtc-sun6i.c | 14 ++++++--------
> >  1 file changed, 6 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/rtc/rtc-sun6i.c b/drivers/rtc/rtc-sun6i.c
> > index 852f5f3b3592..538cf7e19034 100644
> > --- a/drivers/rtc/rtc-sun6i.c
> > +++ b/drivers/rtc/rtc-sun6i.c
> > @@ -250,19 +250,17 @@ static void __init sun6i_rtc_clk_init(struct
> > device_node *node,> 
> >  		writel(reg, rtc->base + SUN6I_LOSC_CTRL);
> >  	
> >  	}
> > 
> > -	/* Switch to the external, more precise, oscillator */
> > -	reg |= SUN6I_LOSC_CTRL_EXT_OSC;
> > -	if (rtc->data->has_losc_en)
> > -		reg |= SUN6I_LOSC_CTRL_EXT_LOSC_EN;
> > +	/* Switch to the external, more precise, oscillator, if present */
> > +	if (of_get_property(node, "clocks", NULL)) {
> > +		reg |= SUN6I_LOSC_CTRL_EXT_OSC;
> > +		if (rtc->data->has_losc_en)
> > +			reg |= SUN6I_LOSC_CTRL_EXT_LOSC_EN;
> > +	}
> > 
> >  	writel(reg, rtc->base + SUN6I_LOSC_CTRL);
> >  	
> >  	/* Yes, I know, this is ugly. */
> >  	sun6i_rtc = rtc;
> > 
> > -	/* Deal with old DTs */
> > -	if (!of_get_property(node, "clocks", NULL))
> > -		goto err;
> > -
> 
> Doesn't that prevent the parents to be properly set if there's an
> external crystal?

No, why?

Check these two clk_summary:
http://ix.io/2bHY Tanix TX6 (no external crystal)
http://ix.io/2bI2 OrangePi 3 (external crystal present)

Please disregard ac200_clk in first case, it's part of another work.

Best regards,
Jernej

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