powerpc/powernv: add hdat attribute to sysfs

The HDAT data area is consumed by skiboot and turned into a device-tree. In some cases we would like to look directly at the HDAT, so this patch adds a sysfs node to allow it to be viewed. This is not possible through /dev/mem as it is reserved memory which is stopped by the /dev/mem filter.

Signed-off-by Matt Brown <[email protected]>

---
Changes between v3 and v4:
- changed sysfs attribute permissions from 0444 to 0400
- fixed makefile to be on same line
- fixed authorship/copyright info
- re-ordered includes
- changed hdat_info struct to a static struct

---
 arch/powerpc/include/asm/opal.h            |  1 +
 arch/powerpc/platforms/powernv/Makefile    |  2 +-
 arch/powerpc/platforms/powernv/opal-hdat.c | 60 ++++++++++++++++++++++++++++++
 arch/powerpc/platforms/powernv/opal.c      |  2 +
 4 files changed, 64 insertions(+), 1 deletion(-)
 create mode 100644 arch/powerpc/platforms/powernv/opal-hdat.c

arch/powerpc/include/asm/opal.h +1 -0

index 5c7db0f..b26944e 100644
@@ -277,6 +277,7 @@ extern int opal_async_comp_init(void);
 extern int opal_sensor_init(void);
 extern int opal_hmi_handler_init(void);
 extern int opal_event_init(void);
+extern void opal_hdat_sysfs_init(void);
 
 extern int opal_machine_check(struct pt_regs *regs);
 extern bool opal_mce_check_early_recovery(struct pt_regs *regs);

arch/powerpc/platforms/powernv/Makefile +1 -1

index b5d98cb..3826b70 100644
@@ -2,7 +2,7 @@ obj-y			+= setup.o opal-wrappers.o opal.o opal-async.o idle.o
 obj-y			+= opal-rtc.o opal-nvram.o opal-lpc.o opal-flash.o
 obj-y			+= rng.o opal-elog.o opal-dump.o opal-sysparam.o opal-sensor.o
 obj-y			+= opal-msglog.o opal-hmi.o opal-power.o opal-irqchip.o
-obj-y			+= opal-kmsg.o
+obj-y			+= opal-kmsg.o opal-hdat.o
 
 obj-$(CONFIG_SMP)	+= smp.o subcore.o subcore-asm.o
 obj-$(CONFIG_PCI)	+= pci.o pci-ioda.o npu-dma.o

arch/powerpc/platforms/powernv/opal-hdat.c new file +28 -0

new file mode 100644
index 0000000..19647fd
@@ -0,0 +1,60 @@
+/*
+ * PowerNV OPAL HDAT interface
+ *
+ * Copyright 2017, Matt Brown, IBM Corp.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ */
+
+#include <linux/of.h>
+#include <linux/types.h>
+#include <asm/io.h>
+#include <asm/opal.h>
+
+static struct {
+	char *base;
+	u64 size;
+} hdat_info;
+
+/* Read function for HDAT attribute in sysfs */
+static ssize_t hdat_read(struct file *file, struct kobject *kobj,
+			 struct bin_attribute *bin_attr, char *to,
+			 loff_t pos, size_t count)
+{
+	if (!hdat_info.base)
+		return -ENODEV;