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

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Message-Id: <DDP09DUCGNDL.24UBAKUA640NO@linaro.org>
Date: Wed, 22 Oct 2025 17:52:23 +0100
From: "Alexey Klimov" <alexey.klimov@...aro.org>
To: "Srinivas Kandagatla" <srinivas.kandagatla@....qualcomm.com>, "Dmitry
 Baryshkov" <dmitry.baryshkov@....qualcomm.com>
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 Tue Oct 21, 2025 at 2:13 PM BST, Srinivas Kandagatla wrote:
>
>
> 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.

No issues. Not sure why the problem (if it exists) wasn't reported or
fixed, say, for sm4250.

Thanks,
Alexey