patch "xhci: Prevent U1/U2 link pm states if exit latency is too long" added to usb-linus

This is a note to let you know that I've just added the patch titled

xhci: Prevent U1/U2 link pm states if exit latency is too long

to my usb git tree which can be found at
git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/usb.git
in the usb-linus branch.

The patch will show up in the next release of the linux-next tree (usually sometime within the next 24 hours during the week.)

The patch will hopefully also be merged in Linus's tree for the next -rc kernel release.

If you have any questions about this process, please let me know.

From: Mathias Nyman <[email protected]>
Date: Wed, 5 Dec 2018 14:22:39 +0200
Subject: xhci: Prevent U1/U2 link pm states if exit latency is too long

Don't allow USB3 U1 or U2 if the latency to wake up from the U-state reaches the service interval for a periodic endpoint.

This is according to xhci 1.1 specification section 4.23.5.2 extra note:

"Software shall ensure that a device is prevented from entering a U-state
where its worst case exit latency approaches the ESIT."

Allowing too long exit latencies for periodic endpoint confuses xHC internal scheduling, and new devices may fail to enumerate with a "Not enough bandwidth for new device state" error from the host.

---
 drivers/usb/host/xhci.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

index c20b85e28d81..dae3be1b9c8f 100644
@@ -4514,6 +4514,14 @@ static u16 xhci_calculate_u1_timeout(struct xhci_hcd *xhci,
 {
 	unsigned long long timeout_ns;
 
+	/* Prevent U1 if service interval is shorter than U1 exit latency */
+	if (usb_endpoint_xfer_int(desc) || usb_endpoint_xfer_isoc(desc)) {
+		if (xhci_service_interval_to_ns(desc) <= udev->u1_params.mel) {
+			dev_dbg(&udev->dev, "Disable U1, ESIT shorter than exit latency\n");
+			return USB3_LPM_DISABLED;
+		}
+	}
+
 	if (xhci->quirks & XHCI_INTEL_HOST)
 		timeout_ns = xhci_calculate_intel_u1_timeout(udev, desc);
 	else

@@ -4570,6 +4578,14 @@ static u16 xhci_calculate_u2_timeout(struct xhci_hcd *xhci,
 {
 	unsigned long long timeout_ns;
 
+	/* Prevent U2 if service interval is shorter than U2 exit latency */
+	if (usb_endpoint_xfer_int(desc) || usb_endpoint_xfer_isoc(desc)) {
+		if (xhci_service_interval_to_ns(desc) <= udev->u2_params.mel) {
+			dev_dbg(&udev->dev, "Disable U2, ESIT shorter than exit latency\n");
+			return USB3_LPM_DISABLED;
+		}
+	}
+
 	if (xhci->quirks & XHCI_INTEL_HOST)
 		timeout_ns = xhci_calculate_intel_u2_timeout(udev, desc);
 	else

2.19.2