drm: add DRM_READ/WRITE64 wrappers around readq/writeq.

The readq/writeq stuff is from Dave Miller, and he
warns users to be careful about using these. Plans are only
r600 to use it so far.
Signed-off-by: Dave Airlie <airlied@redhat.com>

include/drm/drm_os_linux.h

@@ -6,6 +6,19 @@
 #include <linux/interrupt.h>	/* For task queue support */
 #include <linux/delay.h>
 
+#ifndef readq
+static u64 readq(void __iomem *reg)
+{
+	return ((u64) readl(reg)) | (((u64) readl(reg + 4UL)) << 32);
+}
+
+static void writeq(u64 val, void __iomem *reg)
+{
+	writel(val & 0xffffffff, reg);
+	writel(val >> 32, reg + 0x4UL);
+}
+#endif
+
 /** Current process ID */
 #define DRM_CURRENTPID			task_pid_nr(current)
 #define DRM_SUSER(p)			capable(CAP_SYS_ADMIN)
@@ -23,6 +36,12 @@
 /** Write a dword into a MMIO region */
 #define DRM_WRITE32(map, offset, val)	writel(val, ((void __iomem *)(map)->handle) + (offset))
 /** Read memory barrier */
+
+/** Read a qword from a MMIO region - be careful using these unless you really understand them */
+#define DRM_READ64(map, offset)		readq(((void __iomem *)(map)->handle) + (offset))
+/** Write a qword into a MMIO region */
+#define DRM_WRITE64(map, offset, val)	writeq(val, ((void __iomem *)(map)->handle) + (offset))
+
 #define DRM_READMEMORYBARRIER()		rmb()
 /** Write memory barrier */
 #define DRM_WRITEMEMORYBARRIER()	wmb()