[RFC PATCH 2/4] mm/memory_hotplug: Add memory block altmap sysfs attribute

[Sumanth Korikkar <sumanthk@linux.ibm.com>]

Currently memmap_on_memory sysfs attribute can determine if the altmap
is supported in the entire system.

However, with CONFIG_RUNTIME_MEMORY_CONFIGURATION, user can dynamically
add or remove individual memory blocks with/without altmap support.
Hence, it is more beneficial to the user, if the altmap support can also
be represented per memory block.

lsmem output could look like the following:
RANGE                                 SIZE        STATE BLOCK   ALTMAP
0x0000000000000000-0x000000007fffffff   2G       online   0-7   0
0x0000000080000000-0x00000001ffffffff   6G       online  8-31   0
0x0000000200000000-0x00000002ffffffff   4G 	 offline 32-47  1

Reviewed-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Signed-off-by: Sumanth Korikkar <sumanthk@linux.ibm.com>
---
 drivers/base/memory.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/base/memory.c b/drivers/base/memory.c
index f024444b3301..469adc7212fc 100644
--- a/drivers/base/memory.c
+++ b/drivers/base/memory.c
@@ -431,6 +431,14 @@ static ssize_t phys_device_show(struct device *dev,
 			  arch_get_memory_phys_device(start_pfn));
 }
 
+static ssize_t altmap_show(struct device *dev,
+			   struct device_attribute *attr, char *buf)
+{
+	struct memory_block *mem = to_memory_block(dev);
+
+	return sysfs_emit(buf, "%u\n", mem->altmap ? 1 : 0);
+}
+
 #ifdef CONFIG_MEMORY_HOTREMOVE
 static int print_allowed_zone(char *buf, int len, int nid,
 			      struct memory_group *group,
@@ -492,6 +500,7 @@ static DEVICE_ATTR_RO(phys_index);
 static DEVICE_ATTR_RW(state);
 static DEVICE_ATTR_RO(phys_device);
 static DEVICE_ATTR_RO(removable);
+static DEVICE_ATTR_RO(altmap);
 
 /*
  * Show the memory block size (shared by all memory blocks).
@@ -785,6 +794,7 @@ static struct attribute *memory_memblk_attrs[] = {
 #ifdef CONFIG_MEMORY_HOTREMOVE
 	&dev_attr_valid_zones.attr,
 #endif
+	&dev_attr_altmap.attr,
 	NULL
 };
 
-- 
2.45.2