linux-kernel - Re: [PATCH] RFC: arm64: dts: qcom: Disable USB U1/U2 entry for QC targets

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Message-ID: <1d6bb573-6366-49d1-a921-cb04136627a8@quicinc.com>
Date: Mon, 11 Nov 2024 00:45:36 +0530
From: Krishna Kurapati <quic_kriskura@...cinc.com>
To: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
        Bjorn Andersson
	<andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>
CC: <linux-kernel@...r.kernel.org>, <devicetree@...r.kernel.org>,
        Conor Dooley
	<conor+dt@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski
	<krzk+dt@...nel.org>,
        <linux-arm-msm@...r.kernel.org>, <quic_ppratap@...cinc.com>,
        <quic_jackp@...cinc.com>
Subject: Re: [PATCH] RFC: arm64: dts: qcom: Disable USB U1/U2 entry for QC
 targets



On 11/9/2024 2:22 AM, Konrad Dybcio wrote:
> On 7.11.2024 8:36 AM, Krishna Kurapati wrote:
>> Enabling U1 and U2 power-saving states can lead to stability and
>> performance issues, particularly for latency-sensitive or high-
>> throughput applications. These low-power link states are intended
>> to reduce power consumption by allowing the device to enter partial
>> low-power modes during idle periods. However, they can sometimes
>> result in unexpected behavior. Over the years, some of the issues
>> seen are as follows:
>>
>> 1. In device mode of operation, when UVC is active, enabling U1/U2
>> is sometimes causing packets drops due to delay in entry/exit of
>> intermittent low power states. These packet drops are often reflected
>> as Missed Isochronous transfers as the controller was not able to
>> send the packet in that microframe interval and hence glitches are
>> seen on the final transmitted video output.
>>
>> 2. On QCS6490-Rb3Gen2 Vision kit, ADB connection is heavily unstable
>> when U1/U2 is enabled. Often when link enters U2, there is a re-
>> enumeration seen and device is unusable for many use cases.
> 
> Would be nice to enable it on there too, then ;)
> 
> Generally per-file commits are preferred to make potential reverts
> easier down the road
> 

Hi Konrad,

  I agree with you. After the SoB and the "---", I added a paragraph 
mentioning that if this RFC patch looks fine, I will send a series and 
make this change for all SM and QCS targets.

Let me know if the above commit text makes sense. Although I don't have 
all the debug details, I didn't want others in the community face the 
issues we faced and hence the patch.

Regards,
Krishna,