[RFC PATCH 4/5] acpi/hmat: Register special purpose memory as a device

[Dan Williams]

Memory that has been tagged EFI_SPECIAL_PURPOSE, and has performance
properties described by the ACPI HMAT is expected to have an application
specific consumer.

Those consumers may want 100% of the memory capacity to be reserved from
any usage by the kernel. By default, with this enabling, a platform
device is created to represent this differentiated resource.

A follow on change arranges for device-dax to claim these devices by
default and provide an mmap interface for the target application.
However, if the administrator prefers that some or all of the special
purpose memory is made available to the core-mm the device-dax hotplug
facility can be used to online the memory with its own numa node.

Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: Keith Busch <keith.busch@xxxxxxxxx>
Cc: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
---
 drivers/acpi/hmat/Kconfig |    1 +
 drivers/acpi/hmat/hmat.c  |   63 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/memregion.h |    3 ++
 3 files changed, 67 insertions(+)

diff --git a/drivers/acpi/hmat/Kconfig b/drivers/acpi/hmat/Kconfig
index 95a29964dbea..4fcf76e8aa1d 100644
--- a/drivers/acpi/hmat/Kconfig
+++ b/drivers/acpi/hmat/Kconfig
@@ -3,6 +3,7 @@ config ACPI_HMAT
 	bool "ACPI Heterogeneous Memory Attribute Table Support"
 	depends on ACPI_NUMA
 	select HMEM_REPORTING
+	select MEMREGION
 	help
 	 If set, this option has the kernel parse and report the
 	 platform's ACPI HMAT (Heterogeneous Memory Attributes Table),
diff --git a/drivers/acpi/hmat/hmat.c b/drivers/acpi/hmat/hmat.c
index e7ae44c8d359..482360004ea0 100644
--- a/drivers/acpi/hmat/hmat.c
+++ b/drivers/acpi/hmat/hmat.c
@@ -13,6 +13,9 @@
 #include <linux/device.h>
 #include <linux/init.h>
 #include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/memregion.h>
+#include <linux/platform_device.h>
 #include <linux/list_sort.h>
 #include <linux/node.h>
 #include <linux/sysfs.h>
@@ -612,6 +615,65 @@ static __init void hmat_register_target_perf(struct memory_target *target)
 	node_set_perf_attrs(mem_nid, &target->hmem_attrs, 0);
 }
 
+static __init void hmat_register_target_device(struct memory_target *target)
+{
+	struct memregion_info info;
+	struct resource res = {
+		.start = target->start,
+		.end = target->start + target->size - 1,
+		.flags = IORESOURCE_MEM,
+		.desc = IORES_DESC_APPLICATION_RESERVED,
+	};
+	struct platform_device *pdev;
+	int rc, id;
+
+	if (region_intersects(target->start, target->size, IORESOURCE_MEM,
+				IORES_DESC_APPLICATION_RESERVED)
+			!= REGION_INTERSECTS)
+		return;
+
+	id = memregion_alloc();
+	if (id < 0) {
+		pr_err("acpi/hmat: memregion allocation failure for %pr\n", &res);
+		return;
+	}
+
+	pdev = platform_device_alloc("hmem", id);
+	if (!pdev) {
+		pr_err("acpi/hmat: hmem device allocation failure for %pr\n", &res);
+		goto out_pdev;
+	}
+
+	pdev->dev.numa_node = acpi_map_pxm_to_online_node(target->processor_pxm);
+	info = (struct memregion_info) {
+		.target_node = acpi_map_pxm_to_node(target->memory_pxm),
+	};
+	rc = platform_device_add_data(pdev, &info, sizeof(info));
+	if (rc < 0) {
+		pr_err("acpi/hmat: hmem memregion_info allocation failure for %pr\n", &res);
+		goto out_pdev;
+	}
+
+	rc = platform_device_add_resources(pdev, &res, 1);
+	if (rc < 0) {
+		pr_err("acpi/hmat: hmem resource allocation failure for %pr\n", &res);
+		goto out_resource;
+	}
+
+	rc = platform_device_add(pdev);
+	if (rc < 0) {
+		dev_err(&pdev->dev, "acpi/hmat: device add failed for %pr\n", &res);
+		goto out_resource;
+	}
+
+	return;
+
+out_resource:
+	put_device(&pdev->dev);
+out_pdev:
+	memregion_free(id);
+}
+
 static __init void hmat_register_targets(void)
 {
 	struct memory_target *target;
@@ -619,6 +681,7 @@ static __init void hmat_register_targets(void)
 	list_for_each_entry(target, &targets, node) {
 		hmat_register_target_initiators(target);
 		hmat_register_target_perf(target);
+		hmat_register_target_device(target);
 	}
 }
 
diff --git a/include/linux/memregion.h b/include/linux/memregion.h
index 99fa47793b49..5de2ac7fcf5e 100644
--- a/include/linux/memregion.h
+++ b/include/linux/memregion.h
@@ -1,6 +1,9 @@
 // SPDX-License-Identifier: GPL-2.0
 #ifndef _MEMREGION_H_
 #define _MEMREGION_H_
+struct memregion_info {
+	int target_node;
+};
 int memregion_alloc(void);
 void memregion_free(int id);
 #endif /* _MEMREGION_H_ */