s390/dcssblk: Add DAX support

With ZONE_DEVICE now available for s390, struct pages can be allocated
for proper DAX support in dcssblk driver via devm_memremap_pages().

Adding struct pages for a range requires that the range is aligned to
SUBSECTION_SIZE, which is defined as 2 MB in common code. Therefore,
only enable DAX support and allocate struct pages for DCSS ranges that
are aligned to 2 MB.

Signed-off-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com>
Acked-by: Heiko Carstens <hca@linux.ibm.com>
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>

Author: gerald-schaefer

drivers/s390/block/Kconfig

@@ -5,19 +5,11 @@ comment "S/390 block device drivers"
 config DCSSBLK
 	def_tristate m
 	prompt "DCSSBLK support"
-	depends on S390 && BLOCK && (DAX || DAX=n)
+	depends on S390 && BLOCK && ZONE_DEVICE
+	select FS_DAX
 	help
 	  Support for dcss block device
 
-config DCSSBLK_DAX
-	def_bool y
-	depends on DCSSBLK
-	# requires S390 ZONE_DEVICE support
-	depends on BROKEN
-	prompt "DCSSBLK DAX support"
-	help
-	  Enable DAX operation for the dcss block device
-
 config DASD
 	def_tristate y
 	prompt "Support for DASD devices"

drivers/s390/block/dcssblk.c

@@ -79,6 +79,8 @@ struct dcssblk_dev_info {
 	int num_of_segments;
 	struct list_head seg_list;
 	struct dax_device *dax_dev;
+	struct dev_pagemap pgmap;
+	void *pgmap_addr;
 };
 
 struct segment_info {
@@ -415,6 +417,8 @@ dcssblk_shared_store(struct device *dev, struct device_attribute *attr, const ch
 	dax_remove_host(dev_info->gd);
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
+	if (dev_info->pgmap_addr)
+		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
 	del_gendisk(dev_info->gd);
 	put_disk(dev_info->gd);
 
@@ -537,9 +541,6 @@ static int dcssblk_setup_dax(struct dcssblk_dev_info *dev_info)
 {
 	struct dax_device *dax_dev;
 
-	if (!IS_ENABLED(CONFIG_DCSSBLK_DAX))
-		return 0;
-
 	dax_dev = alloc_dax(dev_info, &dcssblk_dax_ops);
 	if (IS_ERR(dax_dev))
 		return PTR_ERR(dax_dev);
@@ -562,6 +563,7 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 	struct dcssblk_dev_info *dev_info;
 	struct segment_info *seg_info, *temp;
 	char *local_buf;
+	void *addr;
 	unsigned long seg_byte_size;
 
 	dev_info = NULL;
@@ -687,9 +689,26 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 	if (rc)
 		goto put_dev;
 
-	rc = dcssblk_setup_dax(dev_info);
-	if (rc)
-		goto out_dax;
+	if (!IS_ALIGNED(dev_info->start, SUBSECTION_SIZE) ||
+	    !IS_ALIGNED(dev_info->end + 1, SUBSECTION_SIZE)) {
+		pr_info("DCSS %s is not aligned to %lu bytes, DAX support disabled\n",
+			local_buf, SUBSECTION_SIZE);
+	} else {
+		dev_info->pgmap.type		= MEMORY_DEVICE_FS_DAX;
+		dev_info->pgmap.range.start	= dev_info->start;
+		dev_info->pgmap.range.end	= dev_info->end;
+		dev_info->pgmap.nr_range	= 1;
+		addr = devm_memremap_pages(&dev_info->dev, &dev_info->pgmap);
+		if (IS_ERR(addr)) {
+			rc = PTR_ERR(addr);
+			goto put_dev;
+		}
+		dev_info->pgmap_addr = addr;
+		rc = dcssblk_setup_dax(dev_info);
+		if (rc)
+			goto out_dax;
+		pr_info("DAX support enabled for DCSS %s\n", local_buf);
+	}
 
 	get_device(&dev_info->dev);
 	rc = device_add_disk(&dev_info->dev, dev_info->gd, NULL);
@@ -716,6 +735,8 @@ dcssblk_add_store(struct device *dev, struct device_attribute *attr, const char
 out_dax:
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
+	if (dev_info->pgmap_addr)
+		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
 put_dev:
 	list_del(&dev_info->lh);
 	put_disk(dev_info->gd);
@@ -801,6 +822,8 @@ dcssblk_remove_store(struct device *dev, struct device_attribute *attr, const ch
 	dax_remove_host(dev_info->gd);
 	kill_dax(dev_info->dax_dev);
 	put_dax(dev_info->dax_dev);
+	if (dev_info->pgmap_addr)
+		devm_memunmap_pages(&dev_info->dev, &dev_info->pgmap);
 	del_gendisk(dev_info->gd);
 	put_disk(dev_info->gd);