[PATCH] usb: pci-quirks: always assert xHCI OS ownership

[Rishabh Jain <rishabh.jain1198@gmail.com>]

The xHCI ownership protocol requires the OS driver to assert the HC OS
Owned semaphore before using the host controller, then wait for HC BIOS
Owned to clear if firmware owns it.

quirk_usb_handoff_xhci() currently asserts OS Owned only when BIOS Owned
is already set. If firmware leaves BIOS Owned clear, Linux uses the xHC
while both ownership semaphores remain clear.

On an AMD PROM21 xHCI controller (1022:43fc), this caused every S3
resume to terminate Controller Restore State with USBSTS 0x401. Linux
then reset the host controller, both root hubs and the USB Bluetooth
adapter.

The controller entered resume ready and halted with USBSTS 0x1.
Endpoint state, 100 ms save/restore delays, scratchpads, the DCBAA,
device contexts and command, event and transfer rings were verified not
to cause the restore error.

Asserting only HC OS Owned changed USBLEGSUP from 0x00000801 to
0x01000801 and eliminated the restore failure across four S3 cycles,
including a stock-kernel test. Clearing USBLEGCTLSTS was independently
verified to be unnecessary.

Always assert OS Owned when the xHCI Legacy Support capability is
present. Use the independently accessible ownership byte so firmware
can update BIOS Owned without racing a 32-bit read-modify-write. Keep
the existing BIOS handoff wait and legacy SMI cleanup unchanged.

Fixes: 66d4eadd8d06 ("USB: xhci: BIOS handoff and HW initialization.")
Tested-by: Rishabh Jain <rishabh.jain1198@gmail.com>
Cc: stable@vger.kernel.org
Signed-off-by: Rishabh Jain <rishabh.jain1198@gmail.com>
---
Additional context:

* Kernel Bugzilla #216470 documents the same USBSTS 0x401/reinitialize
  behavior and its impact on attached USB devices:
  https://bugzilla.kernel.org/show_bug.cgi?id=216470

* Commit a7d57abcc8a5 ("xhci: workaround CSS timeout on AMD SNPS 3.0
  xHC") is related workaround history: it tolerates a distinct AMD CSS
  timeout and resets the controller on resume:
  https://github.com/torvalds/linux/commit/a7d57abcc8a5bdeb53bbf8e87558e8e0a2c2a29d

The external reports do not record their ownership semaphore values but
are included as corroborating failure signatures that this might fix.

drivers/usb/host/pci-quirks.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/drivers/usb/host/pci-quirks.c b/drivers/usb/host/pci-quirks.c
index 0404489c2f6a..d76a4791b8f5 100644
--- a/drivers/usb/host/pci-quirks.c
+++ b/drivers/usb/host/pci-quirks.c
@@ -1185,6 +1185,14 @@ static void quirk_usb_handoff_xhci(struct pci_dev *pdev)
 		dev_warn(&pdev->dev, "xHCI controller failing to respond");
 		goto iounmap;
 	}
+
+	/*
+	 * The OS ownership semaphore must be asserted while the OS owns the
+	 * xHC, even if firmware did not assert the BIOS ownership semaphore.
+	 * Update only the OS ownership byte to avoid racing with firmware.
+	 */
+	writeb(readb(base + ext_cap_offset + 3) | BIT(0),
+	       base + ext_cap_offset + 3);
 	val = readl(base + ext_cap_offset);
 
 	/* Auto handoff never worked for these devices. Force it and continue */
@@ -1195,10 +1203,8 @@ static void quirk_usb_handoff_xhci(struct pci_dev *pdev)
 		writel(val, base + ext_cap_offset);
 	}
 
-	/* If the BIOS owns the HC, signal that the OS wants it, and wait */
+	/* If the BIOS owns the HC, wait for it to hand over control */
 	if (val & XHCI_HC_BIOS_OWNED) {
-		writel(val | XHCI_HC_OS_OWNED, base + ext_cap_offset);
-
 		/* Wait for 1 second with 10 microsecond polling interval */
 		timeout = handshake(base + ext_cap_offset, XHCI_HC_BIOS_OWNED,
 				0, 1000000, 10);
-- 
2.50.1 (Apple Git-155)