linux-kernel - Re: [PATCH v2 08/19] arm64: dts: qcom: Disable USB U1/U2 entry for SA8775P

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Message-ID: <6e9c4ebc-c52e-47ee-b3a5-570e84125e42@oss.qualcomm.com>
Date: Sat, 14 Dec 2024 01:06:16 +0100
From: Konrad Dybcio <konrad.dybcio@....qualcomm.com>
To: Prashanth K <quic_prashk@...cinc.com>,
        Bjorn Andersson <andersson@...nel.org>,
        Konrad Dybcio <konradybcio@...nel.org>, Rob Herring <robh@...nel.org>,
        Krzysztof Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley
 <conor+dt@...nel.org>,
        Krishna Kurapati <krishna.kurapati@....qualcomm.com>
Cc: linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        devicetree@...r.kernel.org, cros-qcom-dts-watchers@...omium.org
Subject: Re: [PATCH v2 08/19] arm64: dts: qcom: Disable USB U1/U2 entry for
 SA8775P

On 13.12.2024 10:52 AM, Prashanth K wrote:
> From: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
> 
> Disable U1 and U2 power-saving states to improve stability of USB.
> These low-power link states, designed to reduce power consumption
> during idle periods, can cause issues in latency-sensitive or high
> throughput use cases. 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 these low power states. These packet drops are often
> reflected as missed isochronous transfers, as the controller wasn't
> able to send 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.
> 
> Disabling these intermittent power states enhances device stability
> without affecting power usage.
> 
> Signed-off-by: Krishna Kurapati <krishna.kurapati@....qualcomm.com>
> Signed-off-by: Prashanth K <quic_prashk@...cinc.com>
> ---

[...]

>  
> @@ -3570,6 +3576,8 @@ tcsr_mutex: hwlock@...0000 {
>  			compatible = "qcom,tcsr-mutex";
>  			reg = <0x0 0x01f40000 0x0 0x20000>;
>  			#hwlock-cells = <1>;
> +				snps,dis-u1-entry-quirk;
> +				snps,dis-u2-entry-quirk;

Oh?

Konrad