linux-kernel - Re: [PATCH] usb: core: Check portchange C_PORT

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Date:   Wed, 3 Oct 2018 09:57:06 -0400 (EDT)
From:   Alan Stern <stern@...land.harvard.edu>
To:     Kai-Heng Feng <kai.heng.feng@...onical.com>
cc:     gregkh@...uxfoundation.org, <linux-usb@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: core: Check portchange C_PORT_RESET after resetting

On Wed, 3 Oct 2018, Kai-Heng Feng wrote:

> Based on USB2.0 Spec Section 11.24.2.7.2.5:
> 
>   "This bit is set when the port transitions from the Resetting state (or,
>   if present, the Speed_eval state) to the Enabled state."
> 
> Also Section 11.24.2.13:
> 
>   "Setting the reset feature PORT_RESET causes the hub to signal reset on
>   that port. When the reset signaling is complete, the hub sets the
>   C_PORT_RESET status change and immediately enables the port."
> 
> So let's also check C_PORT_RESET for reset completion.
> 
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@...onical.com>
> ---
>  drivers/usb/core/hub.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 7801bb30bdba..d96058372280 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -2721,7 +2721,8 @@ static int hub_port_wait_reset(struct usb_hub *hub, int port1,
>  		 * so also wait for the connection to be re-established.
>  		 */
>  		if (!(portstatus & USB_PORT_STAT_RESET) &&
> -		    (portstatus & USB_PORT_STAT_CONNECTION))
> +		    (portstatus & USB_PORT_STAT_CONNECTION) &&
> +		    (portchange & USB_PORT_STAT_C_RESET))
>  			break;
>  
>  		/* switch to the long delay after two short delay failures */

What is the purpose of this patch?  Does it fix a problem?

Alan Stern