Re: [PATCH] arm64: dts: allwinner: h6: tanix-tx6: Use internal oscillator

Hi,

On Thu, Jan 16, 2020 at 05:47:12PM +0100, Jernej Škrabec wrote:

Dne četrtek, 16. januar 2020 ob 09:06:52 CET je Maxime Ripard napisal(a):

quoted

Hi Jernej,

On Mon, Jan 13, 2020 at 07:07:20PM +0100, Jernej Skrabec wrote:

quoted

Tanix TX6 doesn't have external 32 kHz oscillator, so switch RTC clock
to internal one.

Signed-off-by: Jernej Skrabec <redacted>
---

While this patch gives one possible solution, I mainly want to start
discussion why Allwinner SoC dtsi reference external 32 kHz crystal
although some boards don't have it. My proposal would be to make clock
property optional, based on the fact if external crystal is present or
not. However, I'm not sure if that is possible at this point or not.

It's probably a bit of a dumb question but.. are you sure the crystal
is missing?

Although I don't have schematic, I'm pretty sure. Without this patch or one at
[1], RTC gives a lot of errors in dmesg. I think that unpopulated XC2 pads
near SoC (see [2]) are probably reserved for crystal.

With patch in [1], which enables automatic switching in case of error, I saw
that on this box RTC always switched to internal RC.

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The H6 datasheet mentions that the 32kHz crystal needs to be there,
and it's part of the power sequence, so I'd expect all boards to have
it.

Can you be more specific where it is stated that crystal is mandatory?

I was mostly referring to the power sequence mentionned in the H6
Datasheet (not the user manual, the smaller one).

https://linux-sunxi.org/images/5/5c/Allwinner_H6_V200_Datasheet_V1.1.pdf

Page 74

Note that schematic of some boards, like OrangePi PC2 (H5) or OrangePi Zero
(H3) don't even have 32K crystal in them.

And we can't use the compatible for these..

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Driver also considers missing clock property as deprecated (old DT) [1],
so this might complicate things even further.

What do you think?

I'm pretty sure (but that would need to be checked) that we never got
a node without the clocks property on the H6. If that's the case, then
we can add a check on the compatible.

Yes, that would be nice solution. I can work something out if you agree that
this is the way.

So if we want to have something that works for the H3 too, then I
guess we need to revert the patch that switches the 32kHz clock source
to the external one all the time, and do it only if we have a clock
provided.

If we don't, we would run from the internal oscillator (which would
work for both the H3 and H6 boards you have I guess?) and if we do we
will still use the better, more accurate, clock.

That would change a bit the behaviour of the old DTs again and revert
to the old behaviour we had, but we didn't hear anything the first
time we did, so I wouldn't be overly concerned.

Does that make sense?
Maxime