linux-kernel - Re: [PATCH v2] usb: hub: Clear Port Reset Change during init/resume

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Date:	Wed, 16 Oct 2013 10:40:27 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	Julius Werner <jwerner@...omium.org>
cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-kernel@...r.kernel.org>, <linux-usb@...r.kernel.org>,
	Sarah Sharp <sarah.a.sharp@...ux.intel.com>,
	Benson Leung <bleung@...omium.org>,
	Vincent Palatin <vpalatin@...omium.org>,
	Duncan Laurie <dlaurie@...omium.org>
Subject: Re: [PATCH v2] usb: hub: Clear Port Reset Change during init/resume

On Tue, 15 Oct 2013, Julius Werner wrote:

> This patch adds the Port Reset Change flag to the set of bits that are
> preemptively cleared on init/resume of a hub. In theory this bit should
> never be set unexpectedly... in practice it can still happen if BIOS,
> SMM or ACPI code plays around with USB devices without cleaning up
> correctly. This is especially dangerous for XHCI root hubs, which don't
> generate any more Port Status Change Events until all change bits are
> cleared, so this is a good precaution to have (similar to how it's
> already done for the Warm Port Reset Change flag).
> 
> Signed-off-by: Julius Werner <jwerner@...omium.org>
> ---
>  drivers/usb/core/hub.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index e6b682c..c3dd64c 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1130,6 +1130,11 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
>  			usb_clear_port_feature(hub->hdev, port1,
>  					USB_PORT_FEAT_C_ENABLE);
>  		}
> +		if (portchange & USB_PORT_STAT_C_RESET) {
> +			need_debounce_delay = true;
> +			usb_clear_port_feature(hub->hdev, port1,
> +					USB_PORT_FEAT_C_RESET);
> +		}
>  		if ((portchange & USB_PORT_STAT_C_BH_RESET) &&
>  				hub_is_superspeed(hub->hdev)) {
>  			need_debounce_delay = true;

Acked-by: Alan Stern <stern@...land.harvard.edu>

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