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

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Message-ID: <trrbjd574futtatooisumtqp4idqerb5ji2g3nvdesiedlitdd@c6u7wuqhh4r3>
Date: Thu, 7 Nov 2024 13:03:27 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Krishna Kurapati <quic_kriskura@...cinc.com>
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 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?

>  4 files changed, 14 insertions(+)
> 

-- 
With best wishes
Dmitry