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Message-ID: <637796ED17F7774FB27D6AAE3C6951584A929E7C@SZXEMA509-MBS.china.huawei.com>
Date: Tue, 12 Jul 2016 01:45:29 +0000
From: Lipengcheng <lpc.li@...ilicon.com>
To: Alan Stern <stern@...land.harvard.edu>
CC: "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
"baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
"chasemetzger15@...il.com" <chasemetzger15@...il.com>,
"mathias.nyman@...ux.intel.com" <mathias.nyman@...ux.intel.com>,
"oneukum@...e.com" <oneukum@...e.com>,
"jun.li@...escale.com" <jun.li@...escale.com>,
"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH] usb:solve resume usb device identification problem
Hi,
> -----Original Message-----
> From: Alan Stern [mailto:stern@...land.harvard.edu]
> Sent: Monday, July 11, 2016 10:51 PM
> To: Lipengcheng
> Cc: gregkh@...uxfoundation.org; baolu.lu@...ux.intel.com; chasemetzger15@...il.com; mathias.nyman@...ux.intel.com;
> oneukum@...e.com; jun.li@...escale.com; linux-usb@...r.kernel.org; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH] usb:solve resume usb device identification problem
>
> On Mon, 11 Jul 2016, Pengcheng Li wrote:
>
> > A usb device in the connection state. Then host is suspend and resume.
> > But the usb device could not be at the right speed. We should be reset
> > the reset.
> >
> > Signed-off-by: Pengcheng Li <lpc.li@...ilicon.com>
>
> Why wouldn't the USB device be at the right speed?
>
For example, some USB3 devices are resume, the device may be in USB 2.0 Device States. We should have USB 2.0 reset and
make the device into the right speed.
> You should _not_ reset the device if it is at the right speed.
>
> > @@ -3512,6 +3512,10 @@ int usb_port_resume(struct usb_device *udev, pm_message_t msg)
> > }
> > }
> >
> > + retval = hub_port_reset(hub, port1, udev, HUB_ROOT_RESET_TIME, false);
> > + if (retval < 0)
> > + hub_port_disable(hub, port1, 0);
> > +
>
> Most of the time (for example, for non-USB3 devices) this would be wrong.
>
Yes, USB3 devices have this problem. So far, USB2 device can not find this problem.
I mainly refer to the reset process of usb enumeration process.
> Alan Stern
Thanks,
Pengcheng Li
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