[PATCH v14 15/24] x86/resctrl: Add PMT registration API for AET enumeration callbacks

[Tony Luck <tony.luck@intel.com>]

resctrl is always built in and calls into the pmt_telemetry driver to
enumerate Application Energy Telemetry (AET) features. Built-in code cannot
call directly into a module, so AET support requires
CONFIG_INTEL_PMT_TELEMETRY=y.

In preparation for allowing pmt_telemetry to be built as a module, add and
export functions with which pmt_telemetry registers its enumeration
callbacks when it is loaded and unregisters them when it is unloaded.
Record the registering module so that resctrl can hold a reference on it
while it uses the callbacks.

Suggested-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Tony Luck <tony.luck@intel.com>
---
v14:
	New commit message.
---
 include/linux/intel_vsec.h              | 12 ++++++++++++
 arch/x86/kernel/cpu/resctrl/intel_aet.c | 24 ++++++++++++++++++++++++
 2 files changed, 36 insertions(+)

diff --git a/include/linux/intel_vsec.h b/include/linux/intel_vsec.h
index 843cda8f8644..c04b1d0f3143 100644
--- a/include/linux/intel_vsec.h
+++ b/include/linux/intel_vsec.h
@@ -257,4 +257,16 @@ static inline void
 intel_pmt_put_feature_group(struct pmt_feature_group *feature_group) {}
 #endif
 
+#ifdef CONFIG_X86_CPU_RESCTRL_INTEL_AET
+void intel_aet_register_enumeration(struct module *module,
+				    struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+				    void (*put)(struct pmt_feature_group *p));
+void intel_aet_unregister_enumeration(void);
+#else
+static inline void intel_aet_register_enumeration(struct module *module,
+						  struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+						  void (*put)(struct pmt_feature_group *p)) { }
+static inline void intel_aet_unregister_enumeration(void) { }
+#endif /* CONFIG_X86_CPU_RESCTRL_INTEL_AET */
+
 #endif
diff --git a/arch/x86/kernel/cpu/resctrl/intel_aet.c b/arch/x86/kernel/cpu/resctrl/intel_aet.c
index 9f0829a82cb0..996a7ee544bf 100644
--- a/arch/x86/kernel/cpu/resctrl/intel_aet.c
+++ b/arch/x86/kernel/cpu/resctrl/intel_aet.c
@@ -17,12 +17,14 @@
 #include <linux/cpumask.h>
 #include <linux/err.h>
 #include <linux/errno.h>
+#include <linux/export.h>
 #include <linux/gfp_types.h>
 #include <linux/init.h>
 #include <linux/intel_pmt_features.h>
 #include <linux/intel_vsec.h>
 #include <linux/io.h>
 #include <linux/minmax.h>
+#include <linux/module.h>
 #include <linux/printk.h>
 #include <linux/rculist.h>
 #include <linux/rcupdate.h>
@@ -325,6 +327,10 @@ static enum pmt_feature_id lookup_pfid(const char *pfname)
 	return FEATURE_INVALID;
 }
 
+static struct module *pmt_module;
+static struct pmt_feature_group *(*get_feature)(enum pmt_feature_id id);
+static void (*put_feature)(struct pmt_feature_group *p);
+
 /*
  * Request a copy of struct pmt_feature_group for each event group. If there is
  * one, the returned structure has an array of telemetry_region structures,
@@ -359,6 +365,24 @@ bool intel_aet_get_events(void)
 	return ret;
 }
 
+void intel_aet_register_enumeration(struct module *module,
+				    struct pmt_feature_group *(*get)(enum pmt_feature_id id),
+				    void (*put)(struct pmt_feature_group *p))
+{
+	get_feature = get;
+	put_feature = put;
+	pmt_module = module;
+}
+EXPORT_SYMBOL_NS_GPL(intel_aet_register_enumeration, "INTEL_PMT");
+
+void intel_aet_unregister_enumeration(void)
+{
+	pmt_module = NULL;
+	get_feature = NULL;
+	put_feature = NULL;
+}
+EXPORT_SYMBOL_NS_GPL(intel_aet_unregister_enumeration, "INTEL_PMT");
+
 void __exit intel_aet_exit(void)
 {
 	struct event_group **peg;
-- 
2.56.0