The USB core hub thread (khubd) is designed with external USB hubs in
mind. It expects that if a port status change bit is set, the hub will
continue to send a notification through the hub status data transfer.
Basically, it expects hub notifications to be level-triggered.
The xHCI host controller is designed to be edge-triggered. When all
port status change bits are clear, and a new change bit is set, the xHC
will generate a Port Status Change Event. If another change bit is set
in the same port status register before the first bit is cleared, it
will not send another event.
This means that the hub code may lose port status changes because of
race conditions between clearing change bits. The user sees this as a
"dead port" that doesn't react to device connects.
The fix is to turn on port polling whenever a new change bit is set.
Once the USB core issues a hub status request that shows that no change
bits are set in any USB ports, turn off port polling.
We can't allow the USB core to poll the roothub for port events during
host suspend because if the PCI host is in D3cold, the port registers
will be all f's. Instead, stop the port polling timer, and
unconditionally restart it when the host resumes. If there are no port
change bits set after the resume, the first call to hub_status_data will
disable polling.
This patch should be backported to stable kernels with the first xHCI
support, 2.6.31 and newer, that include the commit
0f2a79300a1471cf92ab43af165ea13555c8b0a5 "USB: xhci: Root hub support."
There will be merge conflicts because the check for HC_STATE_SUSPENDED
was moved into xhci_suspend in 3.8.
Signed-off-by: Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
---
drivers/usb/host/xhci-hub.c | 7 +++++++
drivers/usb/host/xhci-ring.c | 7 +++++++
drivers/usb/host/xhci.c | 10 ++++++++++
3 files changed, 24 insertions(+), 0 deletions(-)
diff --git a/drivers/usb/host/xhci-hub.c b/drivers/usb/host/xhci-hub.c
index 4c0cdd0..e873ee6 100644
--- a/drivers/usb/host/xhci-hub.c
+++ b/drivers/usb/host/xhci-hub.c
@@ -984,6 +984,7 @@ int xhci_hub_status_data(struct usb_hcd *hcd, char *buf)
int max_ports;
__le32 __iomem **port_array;
struct xhci_bus_state *bus_state;
+ bool reset_change = false;
max_ports = xhci_get_ports(hcd, &port_array);
bus_state = &xhci->bus_state[hcd_index(hcd)];
@@ -1015,6 +1016,12 @@ int xhci_hub_status_data(struct usb_hcd *hcd, char *buf)
buf[(i + 1) / 8] |= 1 << (i + 1) % 8;
status = 1;
}
+ if ((temp & PORT_RC))
+ reset_change = true;
+ }
+ if (!status && !reset_change) {
+ xhci_dbg(xhci, "%s: stopping port polling.\n", __func__);
+ clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
}
spin_unlock_irqrestore(&xhci->lock, flags);
return status ? retval : 0;
diff --git a/drivers/usb/host/xhci-ring.c b/drivers/usb/host/xhci-ring.c
index cbb44b7..ebb6358 100644
--- a/drivers/usb/host/xhci-ring.c
+++ b/drivers/usb/host/xhci-ring.c
@@ -1725,6 +1725,13 @@ cleanup:
if (bogus_port_status)
return;
+ /*
+ * xHCI portsc bits are level-triggered. An event is sent on the first
+ * change bit, but won't be sent if another change bit is still set.
+ * Poll to avoid losing change bits.
+ */
+ xhci_dbg(xhci, "%s: starting port polling.\n", __func__);
+ set_bit(HCD_FLAG_POLL_RH, &hcd->flags);
spin_unlock(&xhci->lock);
/* Pass this up to the core */
usb_hcd_poll_rh_status(hcd);
diff --git a/drivers/usb/host/xhci.c b/drivers/usb/host/xhci.c
index 5c72c43..f1f01a8 100644
--- a/drivers/usb/host/xhci.c
+++ b/drivers/usb/host/xhci.c
@@ -884,6 +884,11 @@ int xhci_suspend(struct xhci_hcd *xhci)
xhci->shared_hcd->state != HC_STATE_SUSPENDED)
return -EINVAL;
+ /* Don't poll the roothubs on bus suspend. */
+ xhci_dbg(xhci, "%s: stopping port polling.\n", __func__);
+ clear_bit(HCD_FLAG_POLL_RH, &hcd->flags);
+ del_timer_sync(&hcd->rh_timer);
+
spin_lock_irq(&xhci->lock);
clear_bit(HCD_FLAG_HW_ACCESSIBLE, &hcd->flags);
clear_bit(HCD_FLAG_HW_ACCESSIBLE, &xhci->shared_hcd->flags);
@@ -1069,6 +1074,11 @@ int xhci_resume(struct xhci_hcd *xhci, bool hibernated)
if (xhci->quirks & XHCI_COMP_MODE_QUIRK)
compliance_mode_recovery_timer_init(xhci);
+ /* Re-enable port polling. */
+ xhci_dbg(xhci, "%s: starting port polling.\n", __func__);
+ set_bit(HCD_FLAG_POLL_RH, &hcd->flags);
+ usb_hcd_poll_rh_status(hcd);
+
return retval;
}
#endif /* CONFIG_PM */
--
1.7.9
--
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