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

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Message-ID: <01673652-e1fe-4478-bbeb-f532e3358e8f@oss.qualcomm.com>
Date: Sat, 30 Nov 2024 15:39:53 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Krishna Kurapati <quic_kriskura@...cinc.com>,
        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 10.11.2024 8:15 PM, Krishna Kurapati wrote:
> 
> 
> 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.

lgtm

Konrad