On Thu, 9 Jan 2020, Keiya Nobuta wrote: > If hub_activate() is called before D+ has stabilized after remote > wakeup, the following situation might occur: > > __ ___________________ > / \ / > D+ __/ \__/ > > Hub _______________________________ > | ^ ^ ^ > | | | | > Host _____v__|___|___________|______ > | | | | > | | | \-- Interrupt Transfer (*3) > | | \-- ClearPortFeature (*2) > | \-- GetPortStatus (*1) > \-- Host detects remote wakeup > > - D+ goes high, Host starts running by remote wakeup > - D+ is not stable, goes low > - Host requests GetPortStatus at (*1) and gets the following hub status: > - Current Connect Status bit is 0 > - Connect Status Change bit is 1 > - D+ stabilizes, goes high > - Host requests ClearPortFeature and thus Connect Status Change bit is > cleared at (*2) > - After waiting 100 ms, Host starts the Interrupt Transfer at (*3) > - Since the Connect Status Change bit is 0, Hub returns NAK. > > In this case, port_event() is not called in hub_event() and Host cannot > recognize device. To solve this issue, flag change_bits even if only > Connect Status Change bit is 1 when got in the first GetPortStatus. > > This issue occurs rarely because it only if D+ changes during a very > short time between GetPortStatus and ClearPortFeature. However, it is > fatal if it occurs in embedded system. > > Signed-off-by: Keiya Nobuta <nobuta.keiya@xxxxxxxxxxx> > --- > drivers/usb/core/hub.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c > index f229ad6..77f8eb1 100644 > --- a/drivers/usb/core/hub.c > +++ b/drivers/usb/core/hub.c > @@ -1192,6 +1192,7 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type) > * PORT_OVER_CURRENT is not. So check for any of them. > */ > if (udev || (portstatus & USB_PORT_STAT_CONNECTION) || > + (portchange & USB_PORT_STAT_C_CONNECTION) || > (portstatus & USB_PORT_STAT_OVERCURRENT) || > (portchange & USB_PORT_STAT_C_OVERCURRENT)) > set_bit(port1, hub->change_bits); I would have added the new test one line lower, so that all the portstatus checks were adjacent and all the portchange checks were adjacent. But that's a very small thing... Acked-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
