Message-ID: <966635ca-ea10-4e19-a088-62e4b35bc697@kernel.org>
Date: Tue, 27 May 2025 12:57:59 +0200
From: Krzysztof Kozlowski <krzk@...nel.org>
To: Quentin Schulz <quentin.schulz@...rry.de>,
 Quentin Schulz <foss+kernel@...il.net>, Lee Jones <lee@...nel.org>,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>, Heiko Stuebner <heiko@...ech.de>,
 Sebastian Reichel <sebastian.reichel@...labora.com>
Cc: Lukasz Czechowski <lukasz.czechowski@...umatec.com>,
 Daniel Semkowicz <dse@...umatec.com>, devicetree@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-rockchip@...ts.infradead.org,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] dt-bindings: mfd: rk806: allow to customize PMIC
 reset method

On 27/05/2025 11:26, Quentin Schulz wrote:
> Hi Krzysztof,
> 
> On 5/27/25 11:08 AM, Krzysztof Kozlowski wrote:
>> On 27/05/2025 10:48, Quentin Schulz wrote:
>>> Hi Krzysztof,
>>>
>>> On 5/27/25 10:25 AM, Krzysztof Kozlowski wrote:
>>>> On 26/05/2025 19:05, Quentin Schulz wrote:
>>>>> From: Quentin Schulz <quentin.schulz@...rry.de>
>>>>>
>>>>> The RK806 PMIC (and RK809, RK817; but those aren't handled here) has a
>>>>> bitfield for configuring the restart/reset behavior (which I assume
>>>>> Rockchip calls "function") whenever the PMIC is reset (at least by
>>>>> software; c.f. DEV_RST in the datasheet).
>>>>>
>>>>> For RK806, the following values are possible for RST_FUN:
>>>>>
>>>>> 0b00 means "restart PMU"
>>>>> 0b01 means "Reset all the power off reset registers, forcing
>>>>>               the state to switch to ACTIVE mode"
>>>>> 0b10 means "Reset all the power off reset registers, forcing
>>>>>               the state to switch to ACTIVE mode, and simultaneously
>>>>>               pull down the RESETB PIN for 5mS before releasing"
>>>>> 0b11 means the same as for 0b10 just above.
>>>>>
>>>>> I don't believe this is suitable for a subsystem-generic property hence
>>>>> let's make it a vendor property called rockchip,rst-fun.
>>>>>
>>>>> The first few sentences in the description of the property are
>>>>> voluntarily generic so they could be copied to the DT binding for
>>>>> RK809/RK817 whenever someone wants to implement that for those PMIC.
>>>>>
>>>>> Signed-off-by: Quentin Schulz <quentin.schulz@...rry.de>
>>>>> ---
>>>>>    .../devicetree/bindings/mfd/rockchip,rk806.yaml    | 24 ++++++++++++++++++++++
>>>>>    1 file changed, 24 insertions(+)
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/mfd/rockchip,rk806.yaml b/Documentation/devicetree/bindings/mfd/rockchip,rk806.yaml
>>>>> index 3c2b06629b75ea94f90712470bf14ed7fc16d68d..0f931a6da93f7596eac89c5f0deb8ee3bd934c31 100644
>>>>> --- a/Documentation/devicetree/bindings/mfd/rockchip,rk806.yaml
>>>>> +++ b/Documentation/devicetree/bindings/mfd/rockchip,rk806.yaml
>>>>> @@ -31,6 +31,30 @@ properties:
>>>>>    
>>>>>      system-power-controller: true
>>>>>    
>>>>> +  rockchip,rst-fun:
>>>>> +    $ref: /schemas/types.yaml#/definitions/uint32
>>>>> +    enum: [0, 1, 2, 3]
>>>>> +    description:
>>>>> +      RST_FUN value to set for the PMIC.
>>>>> +
>>>>> +      This is the value in the RST_FUN bitfield according to the
>>>>> +      datasheet. I.e. if RST_FUN is bits 6 and 7 and the desired value
>>>>> +      of RST_FUN is 1, this property needs to be set to 1 (and not 64,
>>>>> +      0x40, or BIT(6)).
>>>>> +
>>>>> +      The meaning of this value is specific to the PMIC and is
>>>>> +      explained in the datasheet.
>>>>
>>>> And why would that be exactly board-level configuration? IOW, I expect
>>>> all boards to be reset in the same - correct and optimal - way. Looks
>>>> close to SW policy.
>>>>
>>>
>>> All RK3588 boards except ours in downstream kernel have their RST_FUN
>>> set to 1, we need 0 and I cannot talk for what's the actual expected
>>> behavior for other vendors' boards. I do not feel confident
>>> indiscriminately changing the PMIC reset behavior for all boards using
>>> RK806 (which also includes RK3576 boards). Hence why I made that a property.
>>>
>>> Additionally, if all boards were "to be reset in the same - correct and
>>
>> I don't know if they have to, but that's what I would assume in general.
>> Unless you say there is some specific hardware aspect of your boards,
>> but so far you just described the register.
>>
> 
> The cover letter

We do not read cover letters, except when looking for changelogs.

This patch must stand on its own.

> 
>>> optimal - way", why would Rockchip even have a register for that in the
>>> PMIC? It's not an IP they bought (as far as I could tell), so there's
>>
>> To allow SW to make a choice. Just like 1000 other registers for every
>> other device which we do not add to DT.
>>
>>> likely a purpose to it. Especially if they also change the
>>> silicon-default in their own downstream fork AND provide you with a way
>>> to change their new default from Device Tree.
>>>
>>> We can hardcode the change in the driver without using DT, but I wager
>>> we're going to see a revert in a few releases because it broke some
>>> devices. It may break in subtle ways as well, for example our boards
>>> seem to be working just fine except that because the PMIC doesn't
>>> entirely reset the power rails, our companion microcontroller doesn't
>>> detect the reboot.
>>>
>>> If it's deemed a SW policy by the DT binding people, is there a way to
>>> customize this without having it hardcoded to the same value for all
>>> users of RK806 and without relying on module params?
>>
>> sysfs, reboot mode etc. I don't know what is the right here, because you
>> did not explain the actual hardware issue being fixed here. You only
>> described that bootloader does something, so you want to write something
>> else there.
>>
> 
> We have a companion microcontroller on the PCB of both products which 
> needs to detect if the board was reset. When the board is reset, the MCU 
> FW does a few things, like essentially resetting its internal logic such 
> as the PWM controller (so the beeper stops beeping), watchdogs and 
> reinit most user-exposed registers so that it's like "fresh" out of 
> reset (even though it actually wasn't reset since it's continuously 
> powered, not from the PMIC).

So you miss some wiring to the MCU?

> 
> To detect a reboot, it senses one of the power rails (DCDC8; vcc_3v3_s3 
> on our boards) from the PMIC. This power rail is only "restarted" when 
> RST_FUN is set to 0 ("restart PMU" mode) according to our experiments.
> 
> I assume it is possible other boards do not want this (all?) power rail 
> to be quickly interrupted when rebooting? But that I do not know.

Maybe that's your hardware characteristic which you want to encode in
DT. Don't focus on registers, focus on how the hardware or entire system
is done or different.

Best regards,
Krzysztof

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