[PATCH 4.9 34/51] xhci: Prevent U1/U2 link pm states if exit latency is too long

Greg Kroah-Hartman
2018-12-11T15:49:59Z

From: Mathias Nyman <mathias.nyman@linux.intel.com>

commit 0472bf06c6fd33c1a18aaead4c8f91e5a03d8d7b upstream.

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.

Cc: <stable@vger.kernel.org>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -4398,6 +4398,14 @@ static u16 xhci_calculate_u1_timeout(str
{
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
@@ -4454,6 +4462,14 @@ static u16 xhci_calculate_u2_timeout(str
{
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