[PATCH] powerpc/powernv: Add mmap to opal export sysfs nodes

[Jordan Niethe <jniethe5@gmail.com>]

The sysfs nodes created under /opal/exports/ do not currently support
mmap. Skiboot trace buffers are exported here with in the series
https://patchwork.ozlabs.org/cover/1073501/. Adding mmap support makes
it possible to use the functions for reading traces in external/trace.
This improves on the current read/lseek method as it handles cases like
the buffer wrapping and overflowing.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
v2: ensure only whole pages can be mapped
---
 arch/powerpc/platforms/powernv/opal.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index 2b0eca104f86..3611b5b9c5d2 100644
--- a/arch/powerpc/platforms/powernv/opal.c
+++ b/arch/powerpc/platforms/powernv/opal.c
@@ -714,6 +714,15 @@ static ssize_t export_attr_read(struct file *fp, struct kobject *kobj,
 				       bin_attr->size);
 }
 
+static int export_attr_mmap(struct file *fp, struct kobject *kobj,
+			    struct bin_attribute *attr,
+			    struct vm_area_struct *vma)
+{
+	return remap_pfn_range(vma, vma->vm_start,
+			       __pa(attr->private) >> PAGE_SHIFT,
+			       attr->size, PAGE_READONLY);
+}
+
 /*
  * opal_export_attrs: creates a sysfs node for each property listed in
  * the device-tree under /ibm,opal/firmware/exports/
@@ -759,6 +768,9 @@ static void opal_export_attrs(void)
 		attr->attr.name = kstrdup(prop->name, GFP_KERNEL);
 		attr->attr.mode = 0400;
 		attr->read = export_attr_read;
+		/* Ensure only whole pages are mapped */
+		if (vals[0] % PAGE_SIZE == 0 && vals[1] % PAGE_SIZE == 0)
+			attr->mmap = export_attr_mmap;
 		attr->private = __va(vals[0]);
 		attr->size = vals[1];
 
-- 
2.20.1