linux-kernel - Re: [PATCH v3] USB: Don't set USB_PORT_FEAT

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Message-ID: <20210415184637.GA15445@rowland.harvard.edu>
Date:   Thu, 15 Apr 2021 14:46:37 -0400
From:   Alan Stern <stern@...land.harvard.edu>
To:     Chris Chiu <chris.chiu@...onical.com>
Cc:     Greg KH <gregkh@...uxfoundation.org>, m.v.b@...box.com,
        hadess@...ess.net, linux-usb@...r.kernel.org,
        Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v3] USB: Don't set USB_PORT_FEAT_SUSPEND on WD19's
 Realtek Hub

On Fri, Apr 16, 2021 at 12:13:43AM +0800, Chris Chiu wrote:
> One thing worth mentioning here, I never hit the hub_ext_port_status -71
> problem if I resume by waking up from the keyboard connected to the hub.

I thought you said earlier that the port got into trouble while it was 
suspending, not while it was resuming.  You wrote:

> [ 2789.679812] usb 3-4-port3: can't suspend, status -110

So if the problem occurs during suspend, how can it be possible to avoid 
the problem by taking some particular action later while resuming?

> But the usbcore kernel log shows me wPortStatus: 0503 wPortChane: 0004
> of that port while resuming. In normal cases, they are 0507:0000.

The 0004 bit of wPortChange means that the suspend status has changed; 
the port is no longer suspended because the device attached to that port 
(your keyboard) issued a wakeup request.

>  I don't know how to SetPortFeature() with setting the status change bit only.

You can't.  Only the hub itself can set the wPortChange bits.

> Or maybe it's just some kind of timing issue of the
> idle/suspend/resume signaling.

Not timing.  It's because you woke the system up from the attached 
keyboard.

Alan Stern