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SubjectRe: [PATCH v2] usb: hub: Add delay for SuperSpeed hub resume to let links transit to U0
On Wed, Dec 15, 2021 at 08:01:06PM +0800, Kai-Heng Feng wrote:
> When a new USB device gets plugged to nested hubs, the affected hub,
> which connects to usb 2-1.4-port2, doesn't report there's any change,
> hence the nested hubs go back to runtime suspend like nothing happened:
> [ 281.032951] usb usb2: usb wakeup-resume
> [ 281.032959] usb usb2: usb auto-resume
> [ 281.032974] hub 2-0:1.0: hub_resume
> [ 281.033011] usb usb2-port1: status 0263 change 0000
> [ 281.033077] hub 2-0:1.0: state 7 ports 4 chg 0000 evt 0000
> [ 281.049797] usb 2-1: usb wakeup-resume
> [ 281.069800] usb 2-1: Waited 0ms for CONNECT
> [ 281.069810] usb 2-1: finish resume
> [ 281.070026] hub 2-1:1.0: hub_resume
> [ 281.070250] usb 2-1-port4: status 0203 change 0000
> [ 281.070272] usb usb2-port1: resume, status 0
> [ 281.070282] hub 2-1:1.0: state 7 ports 4 chg 0010 evt 0000
> [ 281.089813] usb 2-1.4: usb wakeup-resume
> [ 281.109792] usb 2-1.4: Waited 0ms for CONNECT
> [ 281.109801] usb 2-1.4: finish resume
> [ 281.109991] hub 2-1.4:1.0: hub_resume
> [ 281.110147] usb 2-1.4-port2: status 0263 change 0000
> [ 281.110234] usb 2-1-port4: resume, status 0
> [ 281.110239] usb 2-1-port4: status 0203, change 0000, 10.0 Gb/s
> [ 281.110266] hub 2-1.4:1.0: state 7 ports 4 chg 0000 evt 0000
> [ 281.110426] hub 2-1.4:1.0: hub_suspend
> [ 281.110565] usb 2-1.4: usb auto-suspend, wakeup 1
> [ 281.130998] hub 2-1:1.0: hub_suspend
> [ 281.137788] usb 2-1: usb auto-suspend, wakeup 1
> [ 281.142935] hub 2-0:1.0: state 7 ports 4 chg 0000 evt 0000
> [ 281.177828] usb 2-1: usb wakeup-resume
> [ 281.197839] usb 2-1: Waited 0ms for CONNECT
> [ 281.197850] usb 2-1: finish resume
> [ 281.197984] hub 2-1:1.0: hub_resume
> [ 281.198203] usb 2-1-port4: status 0203 change 0000
> [ 281.198228] usb usb2-port1: resume, status 0
> [ 281.198237] hub 2-1:1.0: state 7 ports 4 chg 0010 evt 0000
> [ 281.217835] usb 2-1.4: usb wakeup-resume
> [ 281.237834] usb 2-1.4: Waited 0ms for CONNECT
> [ 281.237845] usb 2-1.4: finish resume
> [ 281.237990] hub 2-1.4:1.0: hub_resume
> [ 281.238067] usb 2-1.4-port2: status 0263 change 0000
> [ 281.238148] usb 2-1-port4: resume, status 0
> [ 281.238152] usb 2-1-port4: status 0203, change 0000, 10.0 Gb/s
> [ 281.238166] hub 2-1.4:1.0: state 7 ports 4 chg 0000 evt 0000
> [ 281.238385] hub 2-1.4:1.0: hub_suspend
> [ 281.238523] usb 2-1.4: usb auto-suspend, wakeup 1
> [ 281.258076] hub 2-1:1.0: hub_suspend
> [ 281.265744] usb 2-1: usb auto-suspend, wakeup 1
> [ 281.285976] hub 2-0:1.0: hub_suspend
> [ 281.285988] usb usb2: bus auto-suspend, wakeup 1
>
> USB 3.2 spec, 9.2.5.4 "Changing Function Suspend State" says that "If
> the link is in a non-U0 state, then the device must transition the link
> to U0 prior to sending the remote wake message", but the hub only
> transits the link to U0 after signaling remote wakeup.
>
> So be more forgiving and use a 20ms delay to let the link transit to U0
> for remote wakeup.
>
> Suggested-by: Alan Stern <stern@rowland.harvard.edu>
> Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
> ---
> v2:
> - Add a small delay instead of waking up all hubs.
>
> drivers/usb/core/hub.c | 5 ++++-
> 1 file changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
> index 00070a8a65079..576fdf2c9f3c8 100644
> --- a/drivers/usb/core/hub.c
> +++ b/drivers/usb/core/hub.c
> @@ -1110,7 +1110,10 @@ static void hub_activate(struct usb_hub *hub, enum hub_activation_type type)
> } else {
> hub_power_on(hub, true);
> }
> - }
> + /* Give some time on remote wakeup to let links to transit to U0 */
> + } else if (hub_is_superspeed(hub->hdev))
> + msleep(20);

Where did the 20-ms number come from? Is it mentioned in the spec as
the time required for a port to switch from U3 to U0?

Alan Stern

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