Re: [PATCH v2 2/4] dt-bindings: pinctrl: qcom,tlmm-common: document i2c pull property

[neil.armstrong@linaro.org]

On 25/11/2022 10:47, Linus Walleij wrote:
> On Thu, Nov 24, 2022 at 2:24 PM Neil Armstrong
> <neil.armstrong@linaro.org> wrote:
>> On 24/11/2022 14:11, Linus Walleij wrote:
>>> On Wed, Nov 23, 2022 at 4:20 PM Abel Vesa <abel.vesa@linaro.org> wrote:
>>>
>>>> From: Neil Armstrong <neil.armstrong@linaro.org>
>>>>
>>>> Document the new i2c_pull property introduced for SM8550 setting
>>>> an I2C specific pull mode on I2C able pins.
>>>>
>>>> Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
>>>> Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
>>> (...)
>>>> +      qcom,i2c-pull:
>>>> +        type: boolean
>>>> +        description: enable bias pull feature designed for I2C on pin
>>>
>>> But what is this?
>>>
>>> I2C buses are usually just plain old bias-high-impedance, high-z
>>> or open drain, wire-or or whatever you want to call it.
>>>
>>> But now there is some special i2c mode, huh?
>>>
>>> The description is pretty much "it is what it is"... can we have
>>> some explanation about what this means electrically speaking
>>> and why you cannot use bias-high-impedance?
>>
>> I'll try to get some more info, but so far I only found what I wrote in the bindings.
> 
> Björn: can you see if you can get some clarity about the i2c
> bias thing?

As I understood, it enables an "I2C resistor" on the pin, removing the need
of an external pull-up resistor on the line.

I assume the classical pull-up bias is not strong enough to replace an actual
resistor on the PCB.

Neil

> 
> Yours,
> Linus Walleij