[rtc-linux] Re: [PATCH] rtc: sunxi: use external oscillator

On 06.07.2016 22:20, Maxime Ripard wrote:

On Wed, Jul 06, 2016 at 10:43:00AM +0200, Stephan Roslen wrote:

quoted

+	writel(loscctrl, chip->base + SUNXI_LOSC_CTRL);
+	udelay(100);

=20
Why is that udelay needed?

I found that studying the sunxi 3.4 kernel code and considered it a necessa=
ry delay for the hardware setup and update SUNXI_LOSC_CTRL_SRC_SEL bit. My =
assumption was wrong, it seems. At least a few reboots show, that it is lik=
ely to work without.

=20

quoted

+
+	loscctrl =3D readl(chip->base + SUNXI_LOSC_CTRL);
+	if (!(loscctrl & SUNXI_LOSC_CTRL_SRC_SEL)) {
+		dev_err(&pdev->dev, "Error: Set LOSC to external failed.\n");
+		dev_err(&pdev->dev, "Warning: RTC time will be wrong!\n");
+	}
+

=20
This isn't needed
=20
The issue is actually worse than that.
=20
That register controls the losc source for the whole clock tree, so it
will affect every clock in the system.
=20
In order to have that correctly propagated, you should register a new
mux here in the clock framework, and have all the other clocks using
that mux as a parent.

I agree. Checking the diagram in subsection 1.5.2 of the A20 manual it seem=
s, that LOSC can be a source for clocks like CPU and some SoC busses. So my=
 patch could indeed mess with the whole clock tree.

=20
That's going to be tricky, because the clocks usually probe way
earlier than the RTC driver. So I'm guessing you could do a clock
driver that maps the registers, register its clock, and then when the
RTC probes just takes over what has been setup already by the clock
driver. This also means removing the ability for the RTC to be
compiled as a module.

I agree again. Though I think, the RTC should still work as a module. The C=
LK driver could provide the regmap MFD style and the RTC driver may access =
it. Or rather the CLK driver should use an MFD, that is provided early, too=
. Eventually even a syscon? Actually the whole bunch described in subsectio=
n 1.9 (including timers, arlarms, rtc and even the watchdog) would have to =
rely on that MFD. Do I miss a point?

Stephan

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