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SubjectRe: [PATCH] Revert "usb: Avoid unnecessary LPM enabling and disabling during suspend and resume"
On Wed, 2 Oct 2019, Kai-Heng Feng wrote:

> This reverts commit d590c23111505635e1beb01006612971e5ede8aa.
>
> Dell WD15 dock has a topology like this:
> /: Bus 04.Port 1: Dev 1, Class=root_hub, Driver=xhci_hcd/2p, 10000M
> |__ Port 1: Dev 2, If 0, Class=Hub, Driver=hub/7p, 5000M
> |__ Port 2: Dev 3, If 0, Class=Vendor Specific Class, Driver=r8152, 5000M
>
> Their IDs:
> Bus 004 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
> Bus 004 Device 002: ID 0424:5537 Standard Microsystems Corp.
> Bus 004 Device 004: ID 0bda:8153 Realtek Semiconductor Corp.
>
> Ethernet cannot be detected after plugging ethernet cable to the dock,
> the hub and roothub get runtime resumed and runtime suspended
> immediately:
> ...

> After some trial and errors, the issue goes away if LPM on the SMSC hub
> is disabled. Digging further, enabling and disabling LPM during runtime
> resume and runtime suspend respectively can solve the issue.
>
> So bring back the old LPM behavior, which the SMSC hub inside Dell WD15
> depends on.
>
> Fixes: d590c2311150 ("usb: Avoid unnecessary LPM enabling and disabling during suspend and resume")
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>

Maybe it would be better to have a VID/PID-specific quirk for this?

Alan Stern

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