On Fri, Aug 26, 2022 at 10:55 PM Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
>
> 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?
The specific port means it is connected to a broken accessory.
>
> > Signed-off-by: Ray Chi <raychi@xxxxxxxxxx>
> > ---
> > 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?
>
Because the broken accessory is still connected to the port. Even if we stop
the enumeration attempts, the port change event will issue a new port
initialization.
The implementation is used for dual-role devices, the port power could
be turned on
when the host mode restarts again.
> Why not use the initial_descriptor_timeout module parameter for this
> purpose? That's the sort of thing it was meant for.
>
As I mentioned above, the usbcore driver will keep doing enumeration attempts if
the broken accessory is still connected. It never stops. This is why I
want to turn
off the port to stop enumeration.
> Alan Stern
Thanks,
Ray
