linux-kernel - Re: [PATCH v2 3/4] arm64: dts: qcom: qcm2290: add LPASS LPI pin controller

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Message-ID: <450cac8b-598b-4f47-8bf0-43c805038e7c@oss.qualcomm.com>
Date: Tue, 21 Oct 2025 14:13:57 +0100
From: Srinivas Kandagatla <srinivas.kandagatla@....qualcomm.com>
To: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>,
        Alexey Klimov <alexey.klimov@...aro.org>
Cc: Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>,
        Srinivas Kandagatla <srini@...nel.org>, linux-arm-msm@...r.kernel.org,
        linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sound@...r.kernel.org
Subject: Re: [PATCH v2 3/4] arm64: dts: qcom: qcm2290: add LPASS LPI pin
 controller



On 10/21/25 2:03 PM, Dmitry Baryshkov wrote:
> On Tue, Oct 21, 2025 at 01:56:09PM +0100, Alexey Klimov wrote:
>> On Fri Oct 17, 2025 at 11:42 PM BST, Bjorn Andersson wrote:
>>> On Fri, Oct 10, 2025 at 01:29:38PM +0100, Alexey Klimov wrote:
>>>> On Tue Oct 7, 2025 at 1:39 PM BST, Konrad Dybcio wrote:
>>>>> On 10/7/25 4:03 AM, Alexey Klimov wrote:
>>>>>> Add the Low Power Audio SubSystem Low Power Island (LPASS LPI) pin
>>>>>> controller device node required for audio subsystem on Qualcomm
>>>>>> QRB2210 RB1. QRB2210 is based on qcm2290 which is based on sm6115.
>>>>>>
>>>>>> While at this, also add description of lpi_i2s2 pins (active state)
>>>>>> required for audio playback via HDMI/I2S.
>>>>>>
>>>>>> Cc: Srinivas Kandagatla <srini@...nel.org>
>>>>>> Signed-off-by: Alexey Klimov <alexey.klimov@...aro.org>
>>>>>> ---
>>>>>
>>>>> [...]
>>>>>
>>>>>> +			lpi_i2s2_active: lpi-i2s2-active-state {
>>>>>> +				data-pins {
>>>>>> +					pins = "gpio12";
>>>>>> +					function = "i2s2_data";
>>>>>> +					bias-disable;
>>>>>> +					drive-strength = <8>;
>>>>>> +					output-high;
>>>>>
>>>>> I.. doubt output-high is what you want?
>>>>
>>>> Why? Or is it because of some in-kernel gpiod?
>>>>
>>>
>>> What does "output-high" mean for a non-gpio function?
>>
>> This is not efficient. It will be more useful to go straight to
>> the point.
> 
> It is efficient. It makes everybody think about it (and ask the same
> question in future) instead of just depending on maintainers words.
> 
>> This description of pins was taken from Qualcomm downstream code
>> and the similar patch was applied (see provided URL in the prev email).
> 
> And we all know that downstream can be buggy, incomplete, etc.
> 
>> Back to your question -- does it matter here if it is gpio or non-gpio
>> function?
> 
> It does. The I2S data pin is supposed to be toggled in some way by a
> certain IP core. What would it mean if we program output-high? Will the
> pin still be toggled (by the function) or stay pulled up (because of the
> output being programmed)?
I2S lines are configured in push-pull mode which means that the lines
are driven high and low actively, am not sure why output-high is needed
an what it means here as these lines are actively driven by the controller.

@Alexey, what issues do you see without this?

Am not sure if pinctrl driver even cares about this if we are in alt mode.


--srini>