[PATCH -next] thunderbolt: Add quirk to reset host interface on DMA path teardown for AMD USB4 routers

[Basavaraj Natikar <Basavaraj.Natikar@amd.com>]

Some AMD USB4 host routers have a bug in the Host Interface where
DMA path setup and teardown cycles may cause the Tx ring to hang.

Fix this by issuing a Host Interface Reset on every DMA path teardown
for affected routers. The Host Interface Reset brings the registers in
the memory BAR to their default state and clears the End-to-End Flow
Control state, preventing the hang condition.

Co-developed-by: Sanath S <Sanath.S@amd.com>
Signed-off-by: Sanath S <Sanath.S@amd.com>
Signed-off-by: Basavaraj Natikar <Basavaraj.Natikar@amd.com>
---
 drivers/thunderbolt/nhi.c      | 48 ++++++++++++++++++++++++++++++++++
 drivers/thunderbolt/nhi_regs.h |  4 +++
 drivers/thunderbolt/quirks.c   | 16 ++++++++++++
 drivers/thunderbolt/tb.c       |  7 +++++
 drivers/thunderbolt/tb.h       |  3 +++
 5 files changed, 78 insertions(+)

diff --git a/drivers/thunderbolt/nhi.c b/drivers/thunderbolt/nhi.c
index 383a36212f70..0865cab582e7 100644
--- a/drivers/thunderbolt/nhi.c
+++ b/drivers/thunderbolt/nhi.c
@@ -1160,6 +1160,54 @@ static void nhi_reset(struct tb_nhi *nhi)
 	dev_warn(nhi->dev, "timeout resetting host router\n");
 }
 
+/**
+ * nhi_host_interface_reset() - Issue a host interface reset
+ * @nhi: Pointer to the NHI structure
+ *
+ * Resets the Host Interface by setting the RST bit in the Host Interface
+ * Reset register. This brings the registers in the memory BAR to their
+ * default state and clears the End-to-End Flow Control state.
+ *
+ * The caller must ensure that the control channel (Ring 0) is stopped
+ * before calling this function, since the reset clears ring state.
+ * The caller is responsible for restarting Ring 0 afterward.
+ *
+ * After setting the RST bit, waits for tHIReset (10 ms) for the reset
+ * to complete.
+ */
+static void nhi_host_interface_reset(struct tb_nhi *nhi)
+{
+	struct device *dev = nhi->dev;
+	u32 val;
+
+	val = ioread32(nhi->iobase + REG_CAPS);
+	/* Host Interface Reset only applies to Ver. 1 routers */
+	if (FIELD_GET(REG_CAPS_VERSION_MASK, val) >= REG_CAPS_VERSION_2)
+		return;
+
+	dev_dbg(dev, "issuing host interface reset\n");
+
+	iowrite32(REG_HOST_INTERFACE_RESET_RST,
+		  nhi->iobase + REG_HOST_INTERFACE_RESET);
+
+	/* Wait for tHIReset (10 ms) for the reset to complete */
+	usleep_range(10000, 20000);
+}
+
+/**
+ * tb_nhi_host_interface_reset() - Reset host interface with control channel
+ * @tb: Pointer to the thunderbolt domain
+ *
+ * Stops the control channel, issues a Host Interface Reset, and restarts
+ * the control channel.
+ */
+void tb_nhi_host_interface_reset(struct tb *tb)
+{
+	tb_ctl_stop(tb->ctl);
+	nhi_host_interface_reset(tb->nhi);
+	tb_ctl_start(tb->ctl);
+}
+
 static struct tb *nhi_select_cm(struct tb_nhi *nhi)
 {
 	struct tb *tb;
diff --git a/drivers/thunderbolt/nhi_regs.h b/drivers/thunderbolt/nhi_regs.h
index d6a197fabc74..99df60b6db36 100644
--- a/drivers/thunderbolt/nhi_regs.h
+++ b/drivers/thunderbolt/nhi_regs.h
@@ -115,6 +115,10 @@ struct ring_desc {
 #define REG_CAPS_VERSION_MASK		GENMASK(23, 16)
 #define REG_CAPS_VERSION_2		0x40
 
+/* Host Interface Reset - resets TX/RX rings and E2E flow control counters */
+#define REG_HOST_INTERFACE_RESET	0x39858
+#define REG_HOST_INTERFACE_RESET_RST	BIT(0)
+
 #define REG_DMA_MISC			0x39864
 #define REG_DMA_MISC_INT_AUTO_CLEAR     BIT(2)
 #define REG_DMA_MISC_DISABLE_AUTO_CLEAR	BIT(17)
diff --git a/drivers/thunderbolt/quirks.c b/drivers/thunderbolt/quirks.c
index 9f7914ac2f48..cc04d0873931 100644
--- a/drivers/thunderbolt/quirks.c
+++ b/drivers/thunderbolt/quirks.c
@@ -52,6 +52,12 @@ static void quirk_block_rpm_in_redrive(struct tb_switch *sw)
 	tb_sw_dbg(sw, "preventing runtime PM in DP redrive mode\n");
 }
 
+static void quirk_host_interface_reset(struct tb_switch *sw)
+{
+	sw->quirks |= QUIRK_HOST_INTERFACE_RESET;
+	tb_sw_dbg(sw, "enabling host interface reset on DMA path teardown\n");
+}
+
 struct tb_quirk {
 	u16 hw_vendor_id;
 	u16 hw_device_id;
@@ -114,6 +120,16 @@ static const struct tb_quirk tb_quirks[] = {
 	{ 0x0438, 0x0209, 0x0000, 0x0000, quirk_clx_disable },
 	{ 0x0438, 0x020a, 0x0000, 0x0000, quirk_clx_disable },
 	{ 0x0438, 0x020b, 0x0000, 0x0000, quirk_clx_disable },
+	/*
+	 * AMD USB4 host routers may hang the Tx ring after repeated
+	 * DMA path teardowns. Issue a Host Interface Reset on each
+	 * teardown to prevent the hang.
+	 */
+	{ 0x0438, 0x020d, 0x0000, 0x0000, quirk_host_interface_reset },
+	{ 0x0438, 0x020e, 0x0000, 0x0000, quirk_host_interface_reset },
+	{ 0x0438, 0x020f, 0x0000, 0x0000, quirk_host_interface_reset },
+	{ 0x0438, 0x0210, 0x0000, 0x0000, quirk_host_interface_reset },
+	{ 0x0438, 0x0211, 0x0000, 0x0000, quirk_host_interface_reset },
 };
 
 /**
diff --git a/drivers/thunderbolt/tb.c b/drivers/thunderbolt/tb.c
index 47753a5c0f2e..d40cc9e57364 100644
--- a/drivers/thunderbolt/tb.c
+++ b/drivers/thunderbolt/tb.c
@@ -2395,6 +2395,13 @@ static void __tb_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,
 	 * the same host router USB4 downstream port.
 	 */
 	tb_enable_clx(sw);
+
+	/*
+	 * Some host routers may hang the Tx ring after DMA path teardowns.
+	 * Issue a Host Interface Reset to prevent it.
+	 */
+	if (tb->root_switch->quirks & QUIRK_HOST_INTERFACE_RESET)
+		tb_nhi_host_interface_reset(tb);
 }
 
 static int tb_disconnect_xdomain_paths(struct tb *tb, struct tb_xdomain *xd,
diff --git a/drivers/thunderbolt/tb.h b/drivers/thunderbolt/tb.h
index 4373336d9425..d21feb631f3e 100644
--- a/drivers/thunderbolt/tb.h
+++ b/drivers/thunderbolt/tb.h
@@ -26,6 +26,8 @@
 #define QUIRK_NO_CLX					BIT(1)
 /* Need to keep power on while USB4 port is in redrive mode */
 #define QUIRK_KEEP_POWER_IN_DP_REDRIVE			BIT(2)
+/* Reset Host Interface on DMA path teardown to prevent Tx ring hang */
+#define QUIRK_HOST_INTERFACE_RESET			BIT(3)
 
 /**
  * struct tb_nvm - Structure holding NVM information
@@ -1507,6 +1509,7 @@ static inline bool usb4_port_device_is_offline(const struct usb4_port *usb4)
 }
 
 void tb_check_quirks(struct tb_switch *sw);
+void tb_nhi_host_interface_reset(struct tb *tb);
 
 #ifdef CONFIG_ACPI
 bool tb_acpi_add_links(struct tb_nhi *nhi);
-- 
2.34.1