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. 5. On targets like SDX75, intermittent disconnects were observed with certain cables due to impedence variations. 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. This series was earlier started by Krishna Kurapati where he disabled U1/U2 on some SM targets. I'm extending this to more devices including Auto, Compute and IOT platforms. On a side note, this quirk has been already included on some mobile targets like SM8550/8650. Link to v1: https://lore.kernel.org/all/20241107073650.13473-1-quic_kriskura@xxxxxxxxxxx/#Z31arch:arm64:boot:dts:qcom:sm8250.dtsi Krishna Kurapati (8): arm64: dts: qcom: Disable USB U1/U2 entry for SM8350 arm64: dts: qcom: Disable USB U1/U2 entry for SM8450 arm64: dts: qcom: Disable USB U1/U2 entry for SM8150 arm64: dts: qcom: Disable USB U1/U2 entry for SM6125 arm64: dts: qcom: Disable USB U1/U2 entry for SM8250 arm64: dts: qcom: Disable USB U1/U2 entry for SM6350 arm64: dts: qcom: Disable USB U1/U2 entry for SC7280 arm64: dts: qcom: Disable USB U1/U2 entry for SA8775P Prashanth K (11): arm64: dts: qcom: Disable USB U1/U2 entry for SDM630 arm64: dts: qcom: Disable USB U1/U2 entry for SDM845 arm64: dts: qcom: Disable USB U1/U2 entry for SDX75 ARM: dts: qcom: Disable USB U1/U2 entry for SDX65 ARM: dts: qcom: Disable USB U1/U2 entry for SDX55 arm64: dts: qcom: Disable USB U1/U2 entry for QCS404 arm64: dts: qcom: Disable USB U1/U2 entry for SC7180 arm64: dts: qcom: Disable USB U1/U2 entry for X1E80100 arm64: dts: qcom: Disable USB U1/U2 entry for QDU1000 arm64: dts: qcom: Disable USB U1/U2 entry for SC8280XP arm64: dts: qcom: Disable USB U1/U2 entry for SC8180X arch/arm/boot/dts/qcom/qcom-sdx55.dtsi | 2 ++ arch/arm/boot/dts/qcom/qcom-sdx65.dtsi | 2 ++ arch/arm64/boot/dts/qcom/qcs404.dtsi | 4 ++++ arch/arm64/boot/dts/qcom/qdu1000.dtsi | 2 ++ arch/arm64/boot/dts/qcom/sa8775p.dtsi | 8 ++++++++ arch/arm64/boot/dts/qcom/sc7180.dtsi | 2 ++ arch/arm64/boot/dts/qcom/sc7280.dtsi | 4 ++++ arch/arm64/boot/dts/qcom/sc8180x.dtsi | 6 ++++++ arch/arm64/boot/dts/qcom/sc8280xp.dtsi | 6 ++++++ arch/arm64/boot/dts/qcom/sdm630.dtsi | 4 ++++ arch/arm64/boot/dts/qcom/sdm845.dtsi | 4 ++++ arch/arm64/boot/dts/qcom/sdx75.dtsi | 2 ++ arch/arm64/boot/dts/qcom/sm6125.dtsi | 2 ++ arch/arm64/boot/dts/qcom/sm6350.dtsi | 2 ++ 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 ++ arch/arm64/boot/dts/qcom/x1e80100.dtsi | 10 ++++++++++ 19 files changed, 74 insertions(+) -- 2.25.1
