[PATCH v4 2/8] cxl/acpi: Add root device lockdep validation

[Dan Williams <dan.j.williams@intel.com>]

The CXL "root" device, ACPI0017, is an attach point for coordinating
platform level CXL resources and is the parent device for a CXL port
topology tree. As such it has distinct locking rules relative to other
CXL subsystem objects, but because it is an ACPI device the lock class
is established well before it is given to the cxl_acpi driver.

However, the lockdep API does support changing the lock class "live" for
situations like this. Add a device_lock_set_class() helper that a driver
can use in ->probe() to set a custom lock class, and
device_lock_reset_class() to return to the default "no validate" class
before the custom lock class key goes out of scope after ->remove().

Note the helpers are all macros to support dead code elimination in the
CONFIG_PROVE_LOCKING=n case.

Suggested-by: Peter Zijlstra <peterz@infradead.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Cc: Waiman Long <longman@redhat.com>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Alison Schofield <alison.schofield@intel.com>
Cc: Vishal Verma <vishal.l.verma@intel.com>
Cc: Ben Widawsky <ben.widawsky@intel.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
Changes since v3:
- Add a comment about expected usage of device_lock_set_class() to only
  override the "no validate" class (Ira)
- Clang-format the macros
- Fix device_lock_reset_class() to reset the lock class name to
  "&dev->mutex".

 drivers/cxl/acpi.c     |   15 +++++++++++++++
 include/linux/device.h |   25 +++++++++++++++++++++++++
 2 files changed, 40 insertions(+)

diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
index d15a6aec0331..e19cea27387e 100644
--- a/drivers/cxl/acpi.c
+++ b/drivers/cxl/acpi.c
@@ -275,6 +275,15 @@ static int add_root_nvdimm_bridge(struct device *match, void *data)
 	return 1;
 }
 
+static struct lock_class_key cxl_root_key;
+
+static void cxl_acpi_lock_reset_class(void *_dev)
+{
+	struct device *dev = _dev;
+
+	device_lock_reset_class(dev);
+}
+
 static int cxl_acpi_probe(struct platform_device *pdev)
 {
 	int rc;
@@ -283,6 +292,12 @@ static int cxl_acpi_probe(struct platform_device *pdev)
 	struct acpi_device *adev = ACPI_COMPANION(host);
 	struct cxl_cfmws_context ctx;
 
+	device_lock_set_class(&pdev->dev, &cxl_root_key);
+	rc = devm_add_action_or_reset(&pdev->dev, cxl_acpi_lock_reset_class,
+				      &pdev->dev);
+	if (rc)
+		return rc;
+
 	root_port = devm_cxl_add_port(host, host, CXL_RESOURCE_NONE, NULL);
 	if (IS_ERR(root_port))
 		return PTR_ERR(root_port);
diff --git a/include/linux/device.h b/include/linux/device.h
index 93459724dcde..a4a7c1bf3b72 100644
--- a/include/linux/device.h
+++ b/include/linux/device.h
@@ -850,6 +850,31 @@ static inline bool device_supports_offline(struct device *dev)
 	return dev->bus && dev->bus->offline && dev->bus->online;
 }
 
+#define __device_lock_set_class(dev, name, key)                                \
+	lock_set_class(&(dev)->mutex.dep_map, name, key, 0, _THIS_IP_)
+
+/**
+ * device_lock_set_class - Specify a temporary lock class while a device
+ *			   is attached to a driver
+ * @dev: device to modify
+ * @key: lock class key data
+ *
+ * This must be called with the device_lock() already held, for example
+ * from driver ->probe(). Take care to only override the default
+ * lockdep_no_validate class.
+ */
+#define device_lock_set_class(dev, key) __device_lock_set_class(dev, #key, key)
+
+/**
+ * device_lock_reset_class - Return a device to the default lockdep novalidate state
+ * @dev: device to modify
+ *
+ * This must be called with the device_lock() already held, for example
+ * from driver ->remove().
+ */
+#define device_lock_reset_class(dev)                                           \
+	__device_lock_set_class(dev, "&dev->mutex", &__lockdep_no_validate__)
+
 void lock_device_hotplug(void);
 void unlock_device_hotplug(void);
 int lock_device_hotplug_sysfs(void);