linux-kernel - Re: [PATCH] usb:solve resume usb device identification problem

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Message-ID: <Pine.LNX.4.44L0.1607111047030.27546-100000@netrider.rowland.org>
Date:	Mon, 11 Jul 2016 10:51:02 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Pengcheng Li <lpc.li@...ilicon.com>
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?

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.

Alan Stern