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Date:   Fri, 26 Aug 2022 10:55:41 -0400
From:   Alan Stern <stern@rowland.harvard.edu>
To:     Ray Chi <raychi@google.com>
Cc:     gregkh@linuxfoundation.org, mathias.nyman@linux.intel.com,
        linux-usb@vger.kernel.org, linux-kernel@vger.kernel.org,
        albertccwang@google.com, badhri@google.com, pumahsu@google.com
Subject: Re: [PATCH] usb: core: stop USB enumeration if too many retries
Message-ID: <Ywje7UCqXridmRpw@rowland.harvard.edu>
References: <20220826075839.292615-1-raychi@google.com>
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On Fri, Aug 26, 2022 at 03:58:39PM +0800, Ray Chi wrote:
> If a broken accessory connected to a USB host, usbcore might
> keep doing enumeration retries and it will take a long time to
> cause system unstable.
> 
> This patch provides a quirk to specific USB ports of the hub to
> stop USB enumeration if needed.

Why only to specific ports?

> Signed-off-by: Ray Chi <raychi@google.com>
> ---
>  drivers/usb/core/hub.c | 33 +++++++++++++++++++++++++++++++++
>  include/linux/usb.h    |  3 +++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 2633acde7ac1..0f4097440ffb 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -3081,6 +3081,28 @@ static int hub_port_reset(struct usb_hub *hub, int port1,
>  	return status;
>  }
>  
> +/* Stop enumerate if the port met errors and quirk is set */
> +static bool hub_port_stop_enumerate(struct usb_hub *hub, int port1, int retries)
> +{
> +	struct usb_port *port_dev = hub->ports[port1 - 1];
> +	struct usb_device *hdev = hub->hdev;
> +
> +	if (retries < (PORT_INIT_TRIES - 1) / 2)
> +		return false;
> +
> +	/*
> +	 * Some USB hosts can't take a long time to keep doing enumeration
> +	 * retry. After doing half of the retries, we would turn off the port
> +	 * power to stop enumeration if the quirk is set.
> +	 */
> +	if (port_dev->quirks & USB_PORT_QUIRK_STOP_ENUM) {
> +		usb_hub_set_port_power(hdev, hub, port1, false);

Why turn the port power off?  Aren't there better ways to stop the 
enumeration attempts?  When will the power ever get turned back on?

Why not use the initial_descriptor_timeout module parameter for this 
purpose?  That's the sort of thing it was meant for.

Alan Stern