linux-kernel - Re: [PATCH 0/9] MIPS: CI20: Add WiFi / Bluetooth support

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Date:   Mon, 19 Jun 2023 06:42:46 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     list@...ndingux.net, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        Conor Dooley <conor+dt@...nel.org>, linux-mips@...r.kernel.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Paul Boddie <paul@...die.org.uk>,
        Paul Burton <paulburton@...nel.org>
Subject: Re: [PATCH 0/9] MIPS: CI20: Add WiFi / Bluetooth support

Hi Paul,

> Am 18.06.2023 um 13:51 schrieb Paul Cercueil <paul@...pouillou.net>:

>> And the issue seems to be that without matching the node names the
>> voltages in the device tree may have been ignored completely all the
>> time... Now it sets up voltages, which should happen. But different
>> ones for my board which breaks boot.
> 
> So the node names fix caused the driver to actually use the info from
> DT, which doesn't allow the board to boot. Nice.

Very good summary :)

As usual the fix is just a one-liner, finding what to do is multi-hours.

> 
>> Finally I did risk (I have no replacement CI20 board and they are no
>> longer
>> on sale... RS part# was 125-3305 Mouser 456-VL-62851) to run a test
>> with
>> rename to "DCDC1" but changing the voltage to 1200mV. And this
>> version boots.
> 
> Looking at the JZ4780_DS.PDF file, the SoC actually wants 1.1V so the
> DT is not wrong - in theory. But in practice it does not work, as you
> experienced yourself. However, if the ACT8600 defaults to 1.2V, or if
> the bootloader configures it to 1.2V, I would think that this is
> actually a voltage that the SoC can handle - otherwise the SoC would be
> overvolted until the kernel starts, and the board design would be
> flawed.
> 
> I measured that the old 3.x kernel keeps the SoC voltage at 1.2V, so it
> sounds like a better default. Therefore the fix here would be to raise
> the DCDC1 regulator to 1.2V.

I finally found my JZ4780_DS.pdf (Release Date: Nov. 20, 2014).

According to Table 3-1 the absolute maximum for VDDcore is 1.21V.
According to Table 3-2 the recommended range is 0.99V to 1.21V. 1.1V is only "typical".
According to 1.3 Characteristic: "the Core should run at 1.1 -0.1/+0.2V"

So 1.1V should be right...

But in practise it may be that the ACT8 seems to come up with 1.2V
as chip-internal default during boot. Or U-Boot is initializing it as well.

Maybe I find some time to measure some test point or capacitor while
breaking into U-Boot.

BR,
Nikolaus