[v4,0/2] Disable USB U1/U2 entry for QC ARM targets

Message

Prashanth K Dec. 31, 2024, 8:09 a.m. UTC

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.

Changes in v4:
- Updated prefix in the subject of all patches.
- Split into 2 series for arm and arm64 targets.
- Link to v3:
https://lore.kernel.org/all/[e-mail]/

Changes in v3:
- Removed wrongly added quirks from tcsr_mutex node.
- Link to v2:
https://lore.kernel.org/all/[e-mail]/

Changes in v2:
- RFC patch was split into series of per-file commits.
- Added the quirks to more targets (Auto, IoT, Mobile, Compute).
- Link to RFC:
https://lore.kernel.org/all/[e-mail]/#Z31arch:arm64:boot:dts:qcom:sm8250.dtsi

Prashanth K (2):
  ARM: dts: qcom: sdx65: Disable USB U1/U2 entry
  ARM: dts: qcom: sdx55: Disable USB U1/U2 entry

 arch/arm/boot/dts/qcom/qcom-sdx55.dtsi | 2 ++
 arch/arm/boot/dts/qcom/qcom-sdx65.dtsi | 2 ++
 2 files changed, 4 insertions(+)

Comments

Bjorn Andersson Jan. 7, 2025, 4:38 p.m. UTC | #1

On Tue, 31 Dec 2024 13:39:30 +0530, Prashanth K 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:
> 
> [...]

Applied, thanks!

[1/2] ARM: dts: qcom: sdx65: Disable USB U1/U2 entry
      commit: 5c876b8609026770c63700c21055452fa5641e53
[2/2] ARM: dts: qcom: sdx55: Disable USB U1/U2 entry
      commit: e3bab40d5961453545ef39aeb5198d2e718c9693

Best regards,