[PATCH 7/7] xhci: Detect lpm incapable xHC USB3 roothub ports from ACPI tables

[Mathias Nyman <mathias.nyman@linux.intel.com>]

USB3 ports on xHC hosts may have retimers that cause too long
exit latency to work with native USB3 U1/U2 link power management states.

For now only use usb_acpi_port_lpm_incapable() to evaluate if port lpm
should be disabled while setting up the USB3 roothub.

Other ways to identify lpm incapable ports can be added here later if
ACPI _DSM does not exist.

Limit this to Intel hosts for now, this is to my knowledge only
an Intel issue.

Cc: stable@vger.kernel.org
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
---
 drivers/usb/host/xhci-pci.c | 34 ++++++++++++++++++++++++++++++++++
 1 file changed, 34 insertions(+)

diff --git a/drivers/usb/host/xhci-pci.c b/drivers/usb/host/xhci-pci.c
index b5016709b26f..fb988e4ea924 100644
--- a/drivers/usb/host/xhci-pci.c
+++ b/drivers/usb/host/xhci-pci.c
@@ -355,8 +355,38 @@ static void xhci_pme_acpi_rtd3_enable(struct pci_dev *dev)
 				NULL);
 	ACPI_FREE(obj);
 }
+
+static void xhci_find_lpm_incapable_ports(struct usb_hcd *hcd, struct usb_device *hdev)
+{
+	struct xhci_hcd	*xhci = hcd_to_xhci(hcd);
+	struct xhci_hub *rhub = &xhci->usb3_rhub;
+	int ret;
+	int i;
+
+	/* This is not the usb3 roothub we are looking for */
+	if (hcd != rhub->hcd)
+		return;
+
+	if (hdev->maxchild > rhub->num_ports) {
+		dev_err(&hdev->dev, "USB3 roothub port number mismatch\n");
+		return;
+	}
+
+	for (i = 0; i < hdev->maxchild; i++) {
+		ret = usb_acpi_port_lpm_incapable(hdev, i);
+
+		dev_dbg(&hdev->dev, "port-%d disable U1/U2 _DSM: %d\n", i + 1, ret);
+
+		if (ret >= 0) {
+			rhub->ports[i]->lpm_incapable = ret;
+			continue;
+		}
+	}
+}
+
 #else
 static void xhci_pme_acpi_rtd3_enable(struct pci_dev *dev) { }
+static void xhci_find_lpm_incapable_ports(struct usb_hcd *hcd, struct usb_device *hdev) { }
 #endif /* CONFIG_ACPI */
 
 /* called during probe() after chip reset completes */
@@ -392,6 +422,10 @@ static int xhci_pci_setup(struct usb_hcd *hcd)
 static int xhci_pci_update_hub_device(struct usb_hcd *hcd, struct usb_device *hdev,
 				      struct usb_tt *tt, gfp_t mem_flags)
 {
+	/* Check if acpi claims some USB3 roothub ports are lpm incapable */
+	if (!hdev->parent)
+		xhci_find_lpm_incapable_ports(hcd, hdev);
+
 	return xhci_update_hub_device(hcd, hdev, tt, mem_flags);
 }
 
-- 
2.25.1