[PATCH 16/16] cxl/core, cxl/acpi: Add CXL isolation notify handler

[Ben Cheatham <Benjamin.Cheatham@amd.com>]

Install ACPI 0x80 notify handler for CXL isolation, based on the result
of the _OSC negotiation. The handler is once installed per CXL host bridge
(HID of "ACPI0016") as part of isolation set up.

A link for the ECN (expected in CXL 4.0 spec) that introduces the
relevant parts of the _OSC method (CXL 3.2 9.18.2) can be found below.
spec). This link is only accesible to CXL SSWG members, so here's a brief
overview:

The ECN introduces a field in the _OSC method to control how the OSPM is
notified isolation has occurred. If the ERR_COR Signaling Supported bit
in the isolation capability register (CXL 3.2 8.2.4.24.1) is NOT set,
this portion of the _OSC can be ignored.

If the OSPM is given control of isolation notification, the mechanism to
be used when isolation occurs is an MSI/-X interrupt (pre-ECN behavior).
If the platorm firmware reserves control, the OSPM will be notified
through a ACPI 0x80 notify on the CXL host bridge ACPI device (ACPI HID:
"ACPI0016").

Link: https://members.computeexpresslink.org/wg/software_systems/document/3118
Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
---
 drivers/cxl/acpi.c      | 51 +++++++++++++++++++++++++++++++++++++++++
 drivers/cxl/core/port.c | 41 +++++++++++++++++++++++++--------
 drivers/cxl/cxl.h       |  3 +++
 3 files changed, 86 insertions(+), 9 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index b964f02fb56b..145a03f15255 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -390,10 +390,61 @@ static void decode_isolation_osc(struct cxl_port *hb, u32 iso_cap)
 		hb->isolation_caps |= CXL_ISOLATION_INTERRUPTS;
 }
 
+static void isolation_notify_handler(acpi_handle handle, u32 event, void *data)
+{
+	struct cxl_port *hb = data;
+	struct cxl_dport *dport;
+	unsigned long index;
+
+	guard(device)(&hb->dev);
+	xa_for_each(&hb->dports, index, dport) {
+		if (dport->regs.isolation)
+			cxl_isolation_interrupt_handler(dport);
+	}
+}
+
+static void cxl_remove_iso_handler(void *data)
+{
+	acpi_handle handle = data;
+
+	acpi_remove_notify_handler(handle, ACPI_DEVICE_NOTIFY,
+				   isolation_notify_handler);
+}
+
+static int cxl_register_iso_handler(struct cxl_port *hb)
+{
+	struct acpi_device *adev = ACPI_COMPANION(hb->uport_dev);
+	acpi_handle handle;
+	int rc;
+
+	if (!adev)
+		return -EINVAL;
+
+	handle = acpi_device_handle(adev);
+
+	guard(device)(&hb->dev);
+	if (devm_is_action_added(&hb->dev, cxl_remove_iso_handler, handle))
+		return 0;
+
+	rc = acpi_install_notify_handler(handle, ACPI_DEVICE_NOTIFY,
+					 isolation_notify_handler, hb);
+	if (rc != AE_OK)
+		return -ENXIO;
+
+	rc = devm_add_action_or_reset(&hb->dev, cxl_remove_iso_handler,
+				      handle);
+	if (rc)
+		return rc;
+
+	dev_dbg(&hb->dev, "Installed CXL isolation notify handler\n");
+	return 0;
+}
+
 static const struct cxl_root_ops acpi_root_ops = {
 	.qos_class = cxl_acpi_qos_class,
 	.setup_hostbridge_uport = cxl_acpi_setup_hostbridge_uport,
 	.get_isolation_caps = decode_isolation_osc,
+	.register_hb_isolation_handler = cxl_register_iso_handler,
 };
 
 static void del_cxl_resource(struct resource *res)
diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
index e9eb7a8a5f72..ece667f3aaf5 100644
--- a/drivers/cxl/core/port.c
+++ b/drivers/cxl/core/port.c
@@ -1207,11 +1207,9 @@ struct isolation_intr_data {
 	struct cxl_port *port;
 };
 
-static irqreturn_t cxl_isolation_thread(int irq, void *_data)
+int cxl_isolation_interrupt_handler(struct cxl_dport *dport)
 {
-	struct isolation_intr_data *data = _data;
-	struct cxl_dport *dport = data->dport;
-	struct cxl_port *port = data->port;
+	struct cxl_port *port = dport->port;
 	enum cxl_err_results res, acc;
 	struct cxl_dev_state *cxlds;
 	struct cxl_memdev *cxlmd;
@@ -1221,10 +1219,6 @@ static irqreturn_t cxl_isolation_thread(int irq, void *_data)
 	bool lnk_down;
 	u32 status;
 
-	if (!dport || !port)
-		return IRQ_NONE;
-
-	guard(device)(&port->dev);
 	if (!dport->regs.isolation)
 		goto panic;
 
@@ -1255,8 +1249,9 @@ static irqreturn_t cxl_isolation_thread(int irq, void *_data)
 panic:
 	panic("%s: downstream devices could not recover from CXL.mem link down\n",
 	      dev_name(dport->dport_dev));
-	return IRQ_NONE;
+	return -ENXIO;
 }
+EXPORT_SYMBOL_NS_GPL(cxl_isolation_interrupt_handler, "CXL");
 
 static void cxl_dport_free_interrupts(void *data)
 {
@@ -1274,6 +1269,24 @@ static void cxl_dport_free_interrupts(void *data)
 	devm_free_irq(info->dev, info->irq, dport);
 }
 
+static irqreturn_t cxl_isolation_thread(int irq, void *_data)
+{
+	struct isolation_intr_data *data = _data;
+	struct cxl_dport *dport = data->dport;
+	struct cxl_port *port = data->port;
+	int rc;
+
+	if (!dport || !port)
+		return IRQ_NONE;
+
+	guard(device)(&port->dev);
+	rc = cxl_isolation_interrupt_handler(dport);
+	if (rc)
+		return IRQ_NONE;
+
+	return IRQ_HANDLED;
+}
+
 static int cxl_dport_setup_interrupts(struct device *host,
 				      struct cxl_dport *dport)
 {
@@ -1282,6 +1295,16 @@ static int cxl_dport_setup_interrupts(struct device *host,
 	u32 cap;
 	int rc;
 
+	if (!(dport->port->isolation_caps & CXL_ISOLATION_INTERRUPTS)) {
+		struct cxl_root *root __free(put_cxl_root) =
+			find_cxl_root(dport->port);
+		if (!root || !root->ops ||
+		    !root->ops->register_hb_isolation_handler)
+			return -ENXIO;
+
+		return root->ops->register_hb_isolation_handler(dport->port);
+	}
+
 	cap = readl(dport->regs.isolation + CXL_ISOLATION_CAPABILITY_OFFSET);
 	if (!(cap & CXL_ISOLATION_CAP_INTR_SUPP))
 		return -ENXIO;
diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
index aa36eba79181..68074c0d78d1 100644
--- a/drivers/cxl/cxl.h
+++ b/drivers/cxl/cxl.h
@@ -684,8 +684,11 @@ struct cxl_root_ops {
 				      struct device *bridge_dev);
 	void (*get_isolation_caps)(struct cxl_port *hb,
 				   u32 iso_cap);
+	int (*register_hb_isolation_handler)(struct cxl_port *hb);
 };
 
+int cxl_isolation_interrupt_handler(struct cxl_dport *dport);
+
 static inline struct cxl_dport *
 cxl_find_dport_by_dev(struct cxl_port *port, const struct device *dport_dev)
 {
-- 
2.34.1