From: Vishal Verma <vishal.l.verma@intel.com>

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 for all possible
features.

Based on a patch by Sean Kelley.

Signed-off-by: Vishal Verma <vishal.l.verma@intel.com>
Signed-off-by: Ben Widawsky <redacted>
---
 Documentation/cxl/memory-devices.rst |  15 ++
 drivers/cxl/acpi.c                   | 260 ++++++++++++++++++++++++++-
 drivers/cxl/acpi.h                   |  20 +++
 3 files changed, 292 insertions(+), 3 deletions(-)

diff --git a/Documentation/cxl/memory-devices.rst b/Documentation/cxl/memory-devices.rst
index aa4262280c67..6ce88f9d5f4f 100644
--- a/Documentation/cxl/memory-devices.rst
+++ b/Documentation/cxl/memory-devices.rst

@@ -13,3 +13,18 @@ Driver Infrastructure
 =====================

 This sections covers the driver infrastructure for a CXL memory device.
+
+ACPI CXL
+--------
+
+.. kernel-doc:: drivers/cxl/acpi.c
+   :doc: cxl acpi
+
+.. kernel-doc:: drivers/cxl/acpi.c
+   :internal:
+
+External Interfaces
+===================
+
+.. kernel-doc:: drivers/cxl/acpi.c
+   :export:

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index 0f1ba9b3f1ed..af9c0dfdee20 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c

@@ -11,7 +11,258 @@
 #include <linux/pci.h>
 #include "acpi.h"

-/*
+/**
+ * DOC: cxl acpi
+ *
+ * ACPI _OSC setup: The exported function cxl_bus_acquire() sets up ACPI
+ * Operating System Capabilities (_OSC) for the CXL bus. It declares support
+ * for all CXL capabilities, and attempts to request control for all possible
+ * capabilities. The resulting support and control sets are saved in global
+ * variables cxl_osc_support_set and cxl_osc_control_set. The internal
+ * functions cxl_osc_declare_support(), and cxl_osc_request_control() can be
+ * used to update the support and control sets in accordance with the ACPI
+ * rules for _OSC evaluation - most importantly, capabilities already granted
+ * should not be rescinded by either the OS or firmware.
+ */
+
+static u32 cxl_osc_support_set;
+static u32 cxl_osc_control_set;
+static DEFINE_MUTEX(acpi_desc_lock);
+
+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" },
+};
+
+static u8 cxl_osc_uuid_str[] = "68F2D50B-C469-4d8A-BD3D-941A103FD3FC";
+
+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)