[PATCH v6 04/12] usb: dbc: add support for Intel xHCI dbc quirk

[Lu Baolu]

On Intel platforms, if the debug target is connected with debug
host, enabling DCE bit in command register leads to a port hung
state. In the hung state, the host system will not see a port
connected status bit set. Hence debug target fails to be probed.

The state could be resolved by performing a port reset to the
debug port from the host xHCI. This patch introduces this work
around.

Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
---
 drivers/usb/early/xhci-dbc.c | 52 ++++++++++++++++++++++++++++++++++++++++++++
 include/linux/usb/xhci-dbc.h |  2 ++
 2 files changed, 54 insertions(+)

diff --git a/drivers/usb/early/xhci-dbc.c b/drivers/usb/early/xhci-dbc.c
index 254a0a8..41ce116 100644
--- a/drivers/usb/early/xhci-dbc.c
+++ b/drivers/usb/early/xhci-dbc.c
@@ -255,6 +255,8 @@ static void __iomem *xdbc_map_pci_mmio(u32 bus,
 	xdbcp->bar = bar;
 	xdbcp->xhci_base = base;
 	xdbcp->xhci_length = sz64;
+	xdbcp->vendor = read_pci_config_16(bus, dev, func, PCI_VENDOR_ID);
+	xdbcp->device = read_pci_config_16(bus, dev, func, PCI_DEVICE_ID);
 
 	if (length)
 		*length = sz64;
@@ -638,6 +640,52 @@ static int xdbc_mem_init(void)
 	return 0;
 }
 
+static void xdbc_reset_debug_port_callback(int cap_offset, void *data)
+{
+	u8 major;
+	u32 val, port_offset, port_count;
+	u32 cap_length;
+	void __iomem *ops_reg;
+	void __iomem *portsc;
+	int i;
+
+	val = readl(xdbcp->xhci_base + cap_offset);
+	major = (u8) XHCI_EXT_PORT_MAJOR(val);
+
+	/* only reset super-speed port */
+	if (major != 0x3)
+		return;
+
+	val = readl(xdbcp->xhci_base + cap_offset + 8);
+	port_offset = XHCI_EXT_PORT_OFF(val);
+	port_count = XHCI_EXT_PORT_COUNT(val);
+	xdbc_trace("Extcap Port offset %d count %d\n",
+			port_offset, port_count);
+
+	cap_length = readl(xdbcp->xhci_base) & 0xff;
+	ops_reg = xdbcp->xhci_base + cap_length;
+
+	port_offset--;
+	for (i = port_offset; i < (port_offset + port_count); i++) {
+		portsc = ops_reg + 0x400 + i * 0x10;
+		val = readl(portsc);
+		/* reset the port if CCS bit is cleared */
+		if (!(val & 0x1))
+			writel(val | (1 << 4), portsc);
+	}
+}
+
+static void xdbc_reset_debug_port(void)
+{
+	xdbc_walk_excap(xdbcp->bus,
+			xdbcp->dev,
+			xdbcp->func,
+			XHCI_EXT_CAPS_PROTOCOL,
+			false,
+			xdbc_reset_debug_port_callback,
+			NULL);
+}
+
 /*
  * xdbc_start: start DbC
  *
@@ -656,6 +704,10 @@ static int xdbc_start(void)
 		return -ENODEV;
 	}
 
+	/* reset port to avoid bus hang */
+	if (xdbcp->vendor == PCI_VENDOR_ID_INTEL)
+		xdbc_reset_debug_port();
+
 	/* wait for port connection */
 	if (handshake(&xdbcp->xdbc_reg->portsc, PORTSC_CCS,
 			PORTSC_CCS, 5000000, 100) < 0) {
diff --git a/include/linux/usb/xhci-dbc.h b/include/linux/usb/xhci-dbc.h
index 153fb87..fc0ef9a 100644
--- a/include/linux/usb/xhci-dbc.h
+++ b/include/linux/usb/xhci-dbc.h
@@ -128,6 +128,8 @@ struct xdbc_state {
 	u32		dev;
 	u32		func;
 	u8		bar;
+	u16		vendor;
+	u16		device;
 	void __iomem	*xhci_base;
 	size_t		xhci_length;
 #define	XDBC_PCI_MAX_BUSES		256
-- 
2.1.4