[RFC PATCH 2/9] cxl/acpi: add OSC support

[Ben Widawsky]

From: Vishal Verma <vishal.l.verma@xxxxxxxxx>

Add support to advertise OS capabilities, and request OS control for CXL
features using the ACPI _OSC mechanism. Advertise support for all
possible CXL features, and attempt to request control too for all
possible features.

Based on a patch by Sean Kelley.

Signed-off-by: Vishal Verma <vishal.l.verma@xxxxxxxxx>
Signed-off-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>

---

This uses a non-standard UUID for CXL and is meant as a change proposal
to the CXL specification. The definition for _OSC intermixes PCIe and
CXL Dwords, which makes a clean separation of CXL capabilities
difficult, if not impossible. This is therefore subject to change.

---
 drivers/cxl/acpi.c | 210 ++++++++++++++++++++++++++++++++++++++++++++-
 drivers/cxl/acpi.h |  18 ++++
 2 files changed, 226 insertions(+), 2 deletions(-)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 26e4f73838a7..c3e2f7f6ea02 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -12,6 +12,16 @@
 #include <linux/pci.h>
 #include "acpi.h"
 
+/*
+ * TODO: These are global for now to save the OSC state.
+ * This works if OSC can be expected to be uniform for every ACPI0016 object.
+ * If that is not the case, revisit this. These need to be saved because
+ * relinquishing control of a previously granted capability is disallowed.
+ */
+static u32 cxl_osc_support_set;
+static u32 cxl_osc_control_set;
+static DEFINE_MUTEX(acpi_desc_lock);
+
 static void acpi_cxl_desc_init(struct acpi_cxl_desc *acpi_desc, struct device *dev)
 {
 	dev_set_drvdata(dev, acpi_desc);
@@ -74,6 +84,199 @@ static struct acpi_driver acpi_cxl_driver = {
 	},
 };
 
+struct pci_osc_bit_struct {
+	u32 bit;
+	char *desc;
+};
+
+static struct pci_osc_bit_struct cxl_osc_support_bit[] = {
+	{ CXL_OSC_PORT_REG_ACCESS_SUPPORT, "CXLPortRegAccess" },
+	{ CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT, "CXLPortDevRegAccess" },
+	{ CXL_OSC_PER_SUPPORT, "CXLProtocolErrorReporting" },
+	{ CXL_OSC_NATIVE_HP_SUPPORT, "CXLNativeHotPlug" },
+};
+
+static struct pci_osc_bit_struct cxl_osc_control_bit[] = {
+	{ CXL_OSC_MEM_ERROR_CONTROL, "CXLMemErrorReporting" },
+};
+
+/*
+ * CXL 2.0 spec UUID - unusable as it PCI and CXL OSC are mixed
+ * static u8 cxl_osc_uuid_str[] = "68F2D50B-C469-4d8A-BD3D-941A103FD3FC";
+ */
+/* New, proposed UUID for CXL-only OSC */
+static u8 cxl_osc_uuid_str[] = "A4D1629D-FF52-4888-BE96-E5CADE548DB1";
+
+static void decode_osc_bits(struct device *dev, char *msg, u32 word,
+			    struct pci_osc_bit_struct *table, int size)
+{
+	char buf[80];
+	int i, len = 0;
+	struct pci_osc_bit_struct *entry;
+
+	buf[0] = '\0';
+	for (i = 0, entry = table; i < size; i++, entry++)
+		if (word & entry->bit)
+			len += scnprintf(buf + len, sizeof(buf) - len, "%s%s",
+					len ? " " : "", entry->desc);
+
+	dev_info(dev, "_OSC: %s [%s]\n", msg, buf);
+}
+
+static void decode_cxl_osc_support(struct device *dev, char *msg, u32 word)
+{
+	decode_osc_bits(dev, msg, word, cxl_osc_support_bit,
+			ARRAY_SIZE(cxl_osc_support_bit));
+}
+
+static void decode_cxl_osc_control(struct device *dev, char *msg, u32 word)
+{
+	decode_osc_bits(dev, msg, word, cxl_osc_control_bit,
+			ARRAY_SIZE(cxl_osc_control_bit));
+}
+
+static acpi_status acpi_cap_run_osc(acpi_handle handle,
+				    const u32 *capbuf, u8 *uuid_str, u32 *retval)
+{
+	struct acpi_osc_context context = {
+		.uuid_str = uuid_str,
+		.rev = 1,
+		.cap.length = 20,
+		.cap.pointer = (void *)capbuf,
+	};
+	acpi_status status;
+
+	status = acpi_run_osc(handle, &context);
+	if (ACPI_SUCCESS(status)) {
+		*retval = *((u32 *)(context.ret.pointer + 8));
+		kfree(context.ret.pointer);
+	}
+	return status;
+}
+
+static acpi_status cxl_query_osc(acpi_handle handle, u32 support, u32 *control)
+{
+	acpi_status status;
+	u32 result, capbuf[5];
+
+	support &= CXL_OSC_SUPPORT_VALID_MASK;
+	support |= cxl_osc_support_set;
+
+	capbuf[OSC_QUERY_DWORD] = OSC_QUERY_ENABLE;
+	capbuf[CXL_OSC_SUPPORT_DWORD] = support;
+	if (control) {
+		*control &= CXL_OSC_CONTROL_VALID_MASK;
+		capbuf[CXL_OSC_CONTROL_DWORD] = *control | cxl_osc_control_set;
+	} else {
+		/* Run _OSC query only with existing controls. */
+		capbuf[CXL_OSC_CONTROL_DWORD] = cxl_osc_control_set;
+	}
+
+	status = acpi_cap_run_osc(handle, capbuf, cxl_osc_uuid_str, &result);
+	if (ACPI_SUCCESS(status)) {
+		cxl_osc_support_set = support;
+		if (control)
+			*control = result;
+	}
+	return status;
+}
+
+static acpi_status cxl_osc_advertise_support(acpi_handle handle, u32 flags)
+{
+	acpi_status status;
+
+	mutex_lock(&acpi_desc_lock);
+	status = cxl_query_osc(handle, flags, NULL);
+	mutex_unlock(&acpi_desc_lock);
+	return status;
+}
+
+/**
+ * cxl_osc_request_control - Request control of CXL root _OSC features.
+ * @adev: ACPI device for the PCI root bridge (or PCIe Root Complex).
+ * @mask: Mask of _OSC bits to request control of, place to store control mask.
+ * @req: Mask of _OSC bits the control of is essential to the caller.
+ **/
+static acpi_status cxl_osc_request_control(struct acpi_device *adev, u32 *mask, u32 req)
+{
+	acpi_handle handle = adev->handle;
+	struct device *dev = &adev->dev;
+	acpi_status status = AE_OK;
+	u32 ctrl, capbuf[5];
+
+	if (!mask)
+		return AE_BAD_PARAMETER;
+
+	ctrl = *mask & CXL_OSC_MEM_ERROR_CONTROL;
+	if ((ctrl & req) != req)
+		return AE_TYPE;
+
+	mutex_lock(&acpi_desc_lock);
+
+	*mask = ctrl | cxl_osc_control_set;
+	/* No need to evaluate _OSC if the control was already granted. */
+	if ((cxl_osc_control_set & ctrl) == ctrl)
+		goto out;
+
+	/* Need to check the available controls bits before requesting them. */
+	while (*mask) {
+		status = cxl_query_osc(handle, cxl_osc_support_set, mask);
+		if (ACPI_FAILURE(status))
+			goto out;
+		if (ctrl == *mask)
+			break;
+		decode_cxl_osc_control(dev, "platform does not support", ctrl & ~(*mask));
+		ctrl = *mask;
+	}
+
+	if ((ctrl & req) != req) {
+		decode_cxl_osc_control(dev, "not requesting control; platform does not support",
+				       req & ~(ctrl));
+		status = AE_SUPPORT;
+		goto out;
+	}
+
+	capbuf[OSC_QUERY_DWORD] = 0;
+	capbuf[CXL_OSC_SUPPORT_DWORD] = cxl_osc_support_set;
+	capbuf[CXL_OSC_CONTROL_DWORD] = ctrl;
+	status = acpi_cap_run_osc(handle, capbuf, cxl_osc_uuid_str, mask);
+	if (ACPI_SUCCESS(status))
+		cxl_osc_control_set = *mask;
+out:
+	mutex_unlock(&acpi_desc_lock);
+	return status;
+}
+
+static int cxl_negotiate_osc(struct acpi_device *adev)
+{
+	u32 cxl_support, cxl_control, requested;
+	acpi_handle handle = adev->handle;
+	struct device *dev = &adev->dev;
+	acpi_status status;
+
+	/* Declare support for everything */
+	cxl_support = CXL_OSC_SUPPORT_VALID_MASK;
+	decode_cxl_osc_support(dev, "OS supports", cxl_support);
+	status = cxl_osc_advertise_support(handle, cxl_support);
+	if (ACPI_FAILURE(status)) {
+		dev_info(dev, "CXL_OSC failed (%s)\n", acpi_format_exception(status));
+		return -ENXIO;
+	}
+
+	/* Request control for everything */
+	cxl_control = CXL_OSC_CONTROL_VALID_MASK;
+	requested = cxl_control;
+	status = cxl_osc_request_control(adev, &cxl_control, CXL_OSC_MEM_ERROR_CONTROL);
+	if (ACPI_SUCCESS(status)) {
+		decode_cxl_osc_control(dev, "OS now controls", cxl_control);
+	} else {
+		decode_cxl_osc_control(dev, "OS requested", requested);
+		decode_cxl_osc_control(dev, "platform willing to grant", cxl_control);
+		dev_info(dev, "_OSC failed (%s)\n", acpi_format_exception(status));
+	}
+	return 0;
+}
+
 /*
  * If/when CXL support is defined by other platform firmware the kernel
  * will need a mechanism to select between the platform specific version
@@ -84,6 +287,7 @@ int cxl_bus_prepared(struct pci_dev *pdev)
 	struct acpi_device *adev;
 	struct pci_dev *root_port;
 	struct device *root;
+	int rc;
 
 	root_port = pcie_find_root_port(pdev);
 	if (!root_port)
@@ -97,9 +301,11 @@ int cxl_bus_prepared(struct pci_dev *pdev)
 	if (!adev)
 		return -ENXIO;
 
-	/* TODO: OSC enabling */
+	rc = cxl_negotiate_osc(adev);
+	if (rc)
+		dev_err(&pdev->dev, "Failed to negotiate OSC\n");
 
-	return 0;
+	return rc;
 }
 EXPORT_SYMBOL_GPL(cxl_bus_prepared);
 
diff --git a/drivers/cxl/acpi.h b/drivers/cxl/acpi.h
index 011505475cc6..bf8d078e1b2a 100644
--- a/drivers/cxl/acpi.h
+++ b/drivers/cxl/acpi.h
@@ -10,6 +10,24 @@ struct acpi_cxl_desc {
 	struct device *dev;
 };
 
+/* Indexes into _OSC Capabilities Buffer */
+#define CXL_OSC_SUPPORT_DWORD			1	/* DWORD 2 */
+#define CXL_OSC_CONTROL_DWORD			2	/* DWORD 3 */
+
+/* CXL Host Bridge _OSC: Capabilities DWORD 2: Support Field */
+#define CXL_OSC_PORT_REG_ACCESS_SUPPORT		0x00000001
+#define CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT	0x00000002
+#define CXL_OSC_PER_SUPPORT			0x00000004
+#define CXL_OSC_NATIVE_HP_SUPPORT		0x00000008
+#define CXL_OSC_SUPPORT_VALID_MASK		(CXL_OSC_PORT_REG_ACCESS_SUPPORT |	\
+						 CXL_OSC_PORT_DEV_REG_ACCESS_SUPPORT |	\
+						 CXL_OSC_PER_SUPPORT |			\
+						 CXL_OSC_NATIVE_HP_SUPPORT)
+
+/* CXL Host Bridge _OSC: Capabilities DWORD 3: Control Field */
+#define CXL_OSC_MEM_ERROR_CONTROL		0x00000001
+#define CXL_OSC_CONTROL_VALID_MASK		(CXL_OSC_MEM_ERROR_CONTROL)
+
 int cxl_bus_prepared(struct pci_dev *pci_dev);
 
 #endif	/* __CXL_ACPI_H__ */
-- 
2.29.2