On Sat, Aug 27, 2022 at 01:53:45AM +0800, Ray Chi wrote:
> 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.
Then this patch should be about connections to broken accessories, not
too many retries. The quirk should make the hub driver permanently
ignore the port; whether the power is on or off doesn't matter.
Also, you might want to check whether the port connection is fixed
rather than hot-unpluggable. If the broken accessory can be unplugged
from the port then you don't want to disable the port.
> > > 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.
If you know the accessory is broken then there's no reason to pay
attention to the port change events in the first place. You can simply
make port_event() avoid calling hub_port_connect_change() if the quirk
is set.
Alan Stern
> 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
