Re: [PATCH] usb: core: hub: Improved device recognition on remote wakeup

[Alan Stern <stern@rowland.harvard.edu>]

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@fujitsu.com>
> ---
>  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@rowland.harvard.edu>