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

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Message-ID: <f26bd7ac-5a01-4c9b-b2a0-aa9e65dff6e5@quicinc.com>
Date: Fri, 8 Nov 2024 09:00:52 +0530
From: Krishna Kurapati <quic_kriskura@...cinc.com>
To: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
CC: Krzysztof Kozlowski <krzk+dt@...nel.org>, Rob Herring <robh@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.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 11/7/2024 4:33 PM, Dmitry Baryshkov wrote:
> On Thu, Nov 07, 2024 at 01:06:50PM +0530, 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.
>>
>> 3. On QCS8300/QCS9100, it is observed that when Link enters U2, when
>> the cable is disconnected and reconnected to host PC in HS, there
>> is no link status change interrupt seen and the plug-in in HS doesn't
>> show up a bus reset and enumeration failure happens.
>>
>> 4. On older targets like SM8150/SM8250/SM8350, there have been
>> throughput issues seen during tethering use cases.
>>
>> To avoid such issues, the USB team at Qualcomm added these quirks
>> to all targets in the past 4-5 years and extensive testing was done.
>> Although these are intermittent power states, disabling them didn't
>> cause any major increase in power numbers.
>>
>> Signed-off-by: Krishna Kurapati <quic_kriskura@...cinc.com>
>> ---
>> If this is fine, the patch would be made into a series, disabling
>> U1/U2 for all mobile and QCS targets.
>>
>>   arch/arm64/boot/dts/qcom/sm8150.dtsi | 4 ++++
>>   arch/arm64/boot/dts/qcom/sm8250.dtsi | 4 ++++
>>   arch/arm64/boot/dts/qcom/sm8350.dtsi | 4 ++++
>>   arch/arm64/boot/dts/qcom/sm8450.dtsi | 2 ++
> 
> Should the same set of quirks be applied to SAR2130P too?

Yes, these two quirks have been added to and tested on SAR2130 
downstream. I see that you have added them in your upstream DTSI file 
too. Thanks for that.

Regards,
Krishna,