[PATCH v2 2/2] usb: hub: Disable USB 3 device initiated lpm if exit latency is too high

[Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>]

The device initiated link power management U1/U2 states should not be
enabled in case the system exit latency plus one bus interval (125us) is
greater than the shortest service interval of any periodic endpoint.

This is the case for both U1 and U2 sytstem exit latencies and link states.

See USB 3.2 section 9.4.9 "Set Feature" for more details

Note, before this patch the host and device initiated U1/U2 lpm states
were both enabled with lpm. After this patch it's possible to end up with
only host inititated U1/U2 lpm in case the exit latencies won't allow
device initiated lpm.

If this case we still want to set the udev->usb3_lpm_ux_enabled flag so
that sysfs users can see the link may go to U1/U2.

Signed-off-by: Mathias Nyman <mathias.nyman@xxxxxxxxxxxxxxx>
---
v2: unsigned long long sel not needed, use unsigned int instead.
    Reword commit message

 drivers/usb/core/hub.c | 68 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 56 insertions(+), 12 deletions(-)

diff --git a/drivers/usb/core/hub.c b/drivers/usb/core/hub.c
index a35d0bedafa3..86658a81d284 100644
--- a/drivers/usb/core/hub.c
+++ b/drivers/usb/core/hub.c
@@ -4116,6 +4116,47 @@ static int usb_set_lpm_timeout(struct usb_device *udev,
 	return 0;
 }
 
+/*
+ * Don't allow device intiated U1/U2 if the system exit latency + one bus
+ * interval is greater than the minimum service interval of any active
+ * periodic endpoint. See USB 3.2 section 9.4.9
+ */
+static bool usb_device_may_initiate_lpm(struct usb_device *udev,
+					enum usb3_link_state state)
+{
+	unsigned int sel;		/* us */
+	int i, j;
+
+	if (state == USB3_LPM_U1)
+		sel = DIV_ROUND_UP(udev->u1_params.sel, 1000);
+	else if (state == USB3_LPM_U2)
+		sel = DIV_ROUND_UP(udev->u2_params.sel, 1000);
+	else
+		return false;
+
+	for (i = 0; i < udev->actconfig->desc.bNumInterfaces; i++) {
+		struct usb_interface *intf;
+		struct usb_endpoint_descriptor *desc;
+		unsigned int interval;
+
+		intf = udev->actconfig->interface[i];
+		if (!intf)
+			continue;
+
+		for (j = 0; j < intf->cur_altsetting->desc.bNumEndpoints; j++) {
+			desc = &intf->cur_altsetting->endpoint[j].desc;
+
+			if (usb_endpoint_xfer_int(desc) ||
+			    usb_endpoint_xfer_isoc(desc)) {
+				interval = (1 << (desc->bInterval - 1)) * 125;
+				if (sel + 125 > interval)
+					return false;
+			}
+		}
+	}
+	return true;
+}
+
 /*
  * Enable the hub-initiated U1/U2 idle timeouts, and enable device-initiated
  * U1/U2 entry.
@@ -4188,20 +4229,23 @@ static void usb_enable_link_state(struct usb_hcd *hcd, struct usb_device *udev,
 	 * U1/U2_ENABLE
 	 */
 	if (udev->actconfig &&
-	    usb_set_device_initiated_lpm(udev, state, true) == 0) {
-		if (state == USB3_LPM_U1)
-			udev->usb3_lpm_u1_enabled = 1;
-		else if (state == USB3_LPM_U2)
-			udev->usb3_lpm_u2_enabled = 1;
-	} else {
-		/* Don't request U1/U2 entry if the device
-		 * cannot transition to U1/U2.
-		 */
-		usb_set_lpm_timeout(udev, state, 0);
-		hcd->driver->disable_usb3_lpm_timeout(hcd, udev, state);
+	    usb_device_may_initiate_lpm(udev, state)) {
+		if (usb_set_device_initiated_lpm(udev, state, true)) {
+			/*
+			 * Request to enable device initiated U1/U2 failed,
+			 * better to turn off lpm in this case.
+			 */
+			usb_set_lpm_timeout(udev, state, 0);
+			hcd->driver->disable_usb3_lpm_timeout(hcd, udev, state);
+			return;
+		}
 	}
-}
 
+	if (state == USB3_LPM_U1)
+		udev->usb3_lpm_u1_enabled = 1;
+	else if (state == USB3_LPM_U2)
+		udev->usb3_lpm_u2_enabled = 1;
+}
 /*
  * Disable the hub-initiated U1/U2 idle timeouts, and disable device-initiated
  * U1/U2 entry.
-- 
2.25.1