[PATCH] usb: ehci: skip companion handoff when no companion exists

["William A. Kennington III" <william@wkennington.com>]

EHCI controllers without an integrated root-hub transaction translator
unconditionally set PORT_OWNER whenever a root port sees low-speed line
state before reset, finishes reset without enabling High-Speed mode, or
is relinquished by usbcore after enumeration fails. When no companion
controller is present or enabled, setting PORT_OWNER routes the port
away from EHCI to a nonexistent or disabled controller. A single missed
High-Speed chirp or transient D+/D- bounce during reset then strands
downstream USB 2.0 hubs until EHCI is rebound, and connecting a USB 1.1
device leaves the port dead to later USB 2.0 devices.

Check during ehci_setup() whether HCSPARAMS reports zero companions
(HCS_N_CC == 0), both CONFIG_USB_OHCI_HCD and CONFIG_USB_UHCI_HCD are
disabled in Kconfig (such as in aspeed_g4_defconfig,
aspeed_g5_defconfig, and BMC builds without UHCI or OHCI), or a Device
Tree companion phandle points to a disabled node. Runtime companion
binding is intentionally not checked at setup time so modular or
later-probing companion drivers still receive handoffs.

When no companion is available, set ehci->no_companion to skip
PORT_OWNER handoffs and omit the companion sysfs attribute, matching
the integrated-TT path so usbcore keeps port ownership on EHCI. USB 1.1
full- and low-speed devices still cannot enumerate without an
integrated TT or companion controller and will fail usbcore's normal
reset retries instead of triggering a PORT_OWNER handoff.

Signed-off-by: William A. Kennington III <william@wkennington.com>
---
 drivers/usb/host/ehci-hcd.c   | 31 +++++++++++++++++++++++++++++++
 drivers/usb/host/ehci-hub.c   | 21 ++++++++++-----------
 drivers/usb/host/ehci-sysfs.c |  8 ++++----
 drivers/usb/host/ehci.h       |  1 +
 4 files changed, 46 insertions(+), 15 deletions(-)

diff --git a/drivers/usb/host/ehci-hcd.c b/drivers/usb/host/ehci-hcd.c
index 75f780ec3ba0..1e813ac5f0cb 100644
--- a/drivers/usb/host/ehci-hcd.c
+++ b/drivers/usb/host/ehci-hcd.c
@@ -26,6 +26,7 @@
 #include <linux/moduleparam.h>
 #include <linux/dma-mapping.h>
 #include <linux/debugfs.h>
+#include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/slab.h>
 
@@ -679,6 +680,33 @@ static int ehci_run (struct usb_hcd *hcd)
 	return 0;
 }
 
+static bool ehci_has_companion(struct ehci_hcd *ehci)
+{
+	struct device *dev = ehci_to_hcd(ehci)->self.controller;
+
+	if (HCS_N_CC(ehci->hcs_params) == 0)
+		return false;
+
+	if (!IS_ENABLED(CONFIG_USB_OHCI_HCD) &&
+	    !IS_ENABLED(CONFIG_USB_UHCI_HCD))
+		return false;
+
+	if (dev && dev->of_node) {
+		struct device_node *node;
+
+		node = of_parse_phandle(dev->of_node, "companion", 0);
+		if (node) {
+			bool avail = of_device_is_available(node);
+
+			of_node_put(node);
+			if (!avail)
+				return false;
+		}
+	}
+
+	return true;
+}
+
 int ehci_setup(struct usb_hcd *hcd)
 {
 	struct ehci_hcd *ehci = hcd_to_ehci(hcd);
@@ -691,6 +719,9 @@ int ehci_setup(struct usb_hcd *hcd)
 
 	/* cache this readonly data; minimize chip reads */
 	ehci->hcs_params = ehci_readl(ehci, &ehci->caps->hcs_params);
+	ehci->no_companion = !ehci_has_companion(ehci);
+	if (ehci->no_companion)
+		ehci_dbg(ehci, "no companion controller, disabling port handoff\n");
 
 	ehci->sbrn = HCD_USB2;
 
diff --git a/drivers/usb/host/ehci-hub.c b/drivers/usb/host/ehci-hub.c
index e676c98b6baa..1f69d9fc93c7 100644
--- a/drivers/usb/host/ehci-hub.c
+++ b/drivers/usb/host/ehci-hub.c
@@ -618,18 +618,17 @@ static int check_reset_complete (
 	/* if reset finished and it's still not enabled -- handoff */
 	if (!(port_status & PORT_PE)) {
 
-		/* with integrated TT, there's nobody to hand it to! */
-		if (ehci_is_TDI(ehci)) {
-			ehci_dbg (ehci,
-				"Failed to enable port %d on root hub TT\n",
-				index+1);
+		/* with integrated TT or no companion, there's nobody to hand it to! */
+		if (ehci_is_TDI(ehci) || ehci->no_companion) {
+			ehci_dbg(ehci, "Failed to enable port %d%s\n",
+				 index + 1,
+				 ehci_is_TDI(ehci) ? " on root hub TT" : "");
 			return port_status;
 		}
 
 		ehci_dbg (ehci, "port %d full speed --> companion\n",
 			index + 1);
 
-		// what happens if HCS_N_CC(params) == 0 ?
 		port_status |= PORT_OWNER;
 		port_status &= ~PORT_RWC_BITS;
 		ehci_writel(ehci, port_status, status_reg);
@@ -1145,9 +1144,9 @@ int ehci_hub_control(
 			 * which can be fine if this root hub has a
 			 * transaction translator built in.
 			 */
-			if ((temp & (PORT_PE|PORT_CONNECT)) == PORT_CONNECT
-					&& !ehci_is_TDI(ehci)
-					&& PORT_USB11 (temp)) {
+			if ((temp & (PORT_PE | PORT_CONNECT)) == PORT_CONNECT &&
+			    !ehci_is_TDI(ehci) && !ehci->no_companion &&
+			    PORT_USB11(temp)) {
 				ehci_dbg (ehci,
 					"port %d low speed --> companion\n",
 					wIndex + 1);
@@ -1244,7 +1243,7 @@ static void ehci_relinquish_port(struct usb_hcd *hcd, int portnum)
 {
 	struct ehci_hcd		*ehci = hcd_to_ehci(hcd);
 
-	if (ehci_is_TDI(ehci))
+	if (ehci_is_TDI(ehci) || ehci->no_companion)
 		return;
 	set_owner(ehci, --portnum, PORT_OWNER);
 }
@@ -1254,7 +1253,7 @@ static int ehci_port_handed_over(struct usb_hcd *hcd, int portnum)
 	struct ehci_hcd		*ehci = hcd_to_ehci(hcd);
 	u32 __iomem		*reg;
 
-	if (ehci_is_TDI(ehci))
+	if (ehci_is_TDI(ehci) || ehci->no_companion)
 		return 0;
 	reg = ehci_portsc(ehci, portnum - 1);
 	return ehci_readl(ehci, reg) & PORT_OWNER;
diff --git a/drivers/usb/host/ehci-sysfs.c b/drivers/usb/host/ehci-sysfs.c
index 5e6b545c30e6..1dcca19b544b 100644
--- a/drivers/usb/host/ehci-sysfs.c
+++ b/drivers/usb/host/ehci-sysfs.c
@@ -145,8 +145,8 @@ static inline int create_sysfs_files(struct ehci_hcd *ehci)
 	struct device	*controller = ehci_to_hcd(ehci)->self.controller;
 	int	i = 0;
 
-	/* with integrated TT there is no companion! */
-	if (!ehci_is_TDI(ehci))
+	/* with integrated TT or no_companion there is no companion! */
+	if (!ehci_is_TDI(ehci) && !ehci->no_companion)
 		i = device_create_file(controller, &dev_attr_companion);
 	if (i)
 		goto out;
@@ -160,8 +160,8 @@ static inline void remove_sysfs_files(struct ehci_hcd *ehci)
 {
 	struct device	*controller = ehci_to_hcd(ehci)->self.controller;
 
-	/* with integrated TT there is no companion! */
-	if (!ehci_is_TDI(ehci))
+	/* with integrated TT or no_companion there is no companion! */
+	if (!ehci_is_TDI(ehci) && !ehci->no_companion)
 		device_remove_file(controller, &dev_attr_companion);
 
 	device_remove_file(controller, &dev_attr_uframe_periodic_max);
diff --git a/drivers/usb/host/ehci.h b/drivers/usb/host/ehci.h
index 855a9d08b019..8ab5c696717a 100644
--- a/drivers/usb/host/ehci.h
+++ b/drivers/usb/host/ehci.h
@@ -238,6 +238,7 @@ struct ehci_hcd {			/* one per controller */
 	unsigned		no_configured_flag:1;
 	unsigned		no_tdi_mode:1;
 	unsigned		no_fsls_isoc:1;
+	unsigned		no_companion:1;
 
 	/* required for usb32 quirk */
 	#define OHCI_CTRL_HCFS          (3 << 6)
-- 
2.56.0.611.g1030f0b940-goog