ACPI: MRRM: Minimal parse of ACPI MRRM table

The resctrl file system code needs to know how many region tags
are supported. Parse the ACPI MRRM table and save the max_mem_region
value.

Provide a function for resctrl to collect that value.

Signed-off-by: Tony Luck <tony.luck@intel.com>
Link: https://patch.msgid.link/20250505173819.419271-2-tony.luck@intel.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 42 insertions, 0 deletions

diff --git a/drivers/acpi/acpi_mrrm.c b/drivers/acpi/acpi_mrrm.c
new file mode 100644
index 000000000000..ab8022e58da5
--- /dev/null
+++ b/drivers/acpi/acpi_mrrm.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2025, Intel Corporation.
+ *
+ * Memory Range and Region Mapping (MRRM) structure
+ */
+
+#define pr_fmt(fmt) "acpi/mrrm: " fmt
+
+#include <linux/acpi.h>
+#include <linux/init.h>
+
+static int max_mem_region = -ENOENT;
+
+/* Access for use by resctrl file system */
+int acpi_mrrm_max_mem_region(void)
+{
+	return max_mem_region;
+}
+
+static __init int acpi_parse_mrrm(struct acpi_table_header *table)
+{
+	struct acpi_table_mrrm *mrrm;
+
+	mrrm = (struct acpi_table_mrrm *)table;
+	if (!mrrm)
+		return -ENODEV;
+
+	max_mem_region = mrrm->max_mem_region;
+
+	return 0;
+}
+
+static __init int mrrm_init(void)
+{
+	int ret;
+
+	ret = acpi_table_parse(ACPI_SIG_MRRM, acpi_parse_mrrm);
+
+	return ret;
+}
+device_initcall(mrrm_init);