Date:   Tue, 21 Mar 2023 07:42:37 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Stephan Gerhold <stephan@...hold.net>
Cc:     "Lin, Meng-Bo" <linmengbo0689@...tonmail.com>,
        linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
        Lee Jones <lee@...nel.org>, Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Nikita Travkin <nikita@...n.ru>, linux-leds@...r.kernel.org,
        devicetree@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht
Subject: Re: [PATCH v2 1/2] dt-bindings: leds: aw2013: Document vddio-supply

On 20/03/2023 19:59, Stephan Gerhold wrote:
> On Mon, Mar 20, 2023 at 07:04:22PM +0100, Krzysztof Kozlowski wrote:
>> On 20/03/2023 18:55, Lin, Meng-Bo wrote:
>>> Some LEDs controllers are used with external pull-up for the interrupt
>>> line and the I2C lines, so we might need to enable a regulator to bring
>>> the lines into usable state.
>>
>> Not a property of this device.
>>
>>> Otherwise, this might cause spurious
>>> interrupts and reading from I2C will fail.
>>>
>>> Document support for "vddio-supply" that is enabled by the aw2013 driver
>>> so that the regulator gets enabled when needed.
>>>
>>> Signed-off-by: Lin, Meng-Bo <linmengbo0689@...tonmail.com>
>>> ---
>>>  Documentation/devicetree/bindings/leds/leds-aw2013.yaml | 5 +++++
>>>  1 file changed, 5 insertions(+)
>>>
>>> diff --git a/Documentation/devicetree/bindings/leds/leds-aw2013.yaml b/Documentation/devicetree/bindings/leds/leds-aw2013.yaml
>>> index 08f3e1cfc1b1..79b69cf1d1fe 100644
>>> --- a/Documentation/devicetree/bindings/leds/leds-aw2013.yaml
>>> +++ b/Documentation/devicetree/bindings/leds/leds-aw2013.yaml
>>> @@ -23,6 +23,11 @@ properties:
>>>    vcc-supply:
>>>      description: Regulator providing power to the "VCC" pin.
>>>  
>>> +  vddio-supply:
>>> +    description: |
>>> +      Optional regulator that provides digital I/O voltage,
>>
>> NAK. I responded to your patch and you just send a v2 without explanation.
>>
>> The device does not have VDDIO pin, either.
>>
> 
> The power supply Lin is trying to add here is basically the "VIO1"
> example in "Figure 1 AW2013 Typical Application Circuit" on page 1 of
> the AW2013 datasheet [1]. The I2C pins and the interrupt output are both
> open-drain and therefore require external pull-up resistors, connected
> to a power supply that might not be always on.
> 
> Because of the open-drain pins AW2013 does indeed not have a dedicated
> input pin for the I/O supply voltage. However, it is still necessary to
> describe the power supply _somewhere_, to ensure that it is enabled when
> needed.
> 
> It is hard to model this properly but it's generally easiest to handle
> this inside the peripheral driver since it knows exactly when I2C and/or
> interrupt lines are currently needed or not. This situation is fairly
> common for I2C devices so there are several precedents, e.g.:
> 
>   1. cypress,tm2-touchkey.yaml: "vddio-supply"
>      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=3e730ec11d51283ad62a98436967c01b718132ab
>   2. goodix,gt7375p.yaml: "mainboard-vddio-supply"
>      https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1d18c1f3b7d938bdefc44289d137b4e6c7a3d502

Both are mistaken. How can you enumerate or autodetect a device if its
regulator pulling up I2C are not on? What's more, on I2C lines you could
have more devices, so you expect each of them having the supply?

These are properties of I2C controller, not the consumer. I2C controller
should enable any regulators necessary for the IO pins.

Best regards,
Krzysztof

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