[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 not yet added to this location but
this is a suitable for them to be exported to. Adding mmap support makes
using these trace buffers more convenient. The state in the header of
the trace buffer is needed to ensure the read position has not been
overwritten. Thus the header of the buffer must be read, then the
read position itself. Using lseek/read to do this introduces a delay
that could result in incorrect reads if the read position is overwritten
after the header is read.

Signed-off-by: Jordan Niethe <jniethe5@gmail.com>
---
 arch/powerpc/platforms/powernv/opal.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/powerpc/platforms/powernv/opal.c b/arch/powerpc/platforms/powernv/opal.c
index 2b0eca104f86..3cfc683bb060 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 +768,7 @@ static void opal_export_attrs(void)
 		attr->attr.name = kstrdup(prop->name, GFP_KERNEL);
 		attr->attr.mode = 0400;
 		attr->read = export_attr_read;
+		attr->mmap = export_attr_mmap;
 		attr->private = __va(vals[0]);
 		attr->size = vals[1];
 
-- 
2.20.1