iopoll: import include/linux/iopoll.h from Linux 4.9

This was imported from Linux 4.9 and adjusted for U-Boot.

 - Replace the license block with SPDX
 - Drop all *_atomic variants, which make no sense for U-Boot
 - Remove the sleep_us argument, which makes no sense for U-Boot

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

include/linux/iopoll.h

@@ -0,0 +1,68 @@
+/*
+ * Copyright (c) 2012-2014 The Linux Foundation. All rights reserved.
+ *
+ * SPDX-License-Identifier:	GPL-2.0
+ */
+
+#ifndef _LINUX_IOPOLL_H
+#define _LINUX_IOPOLL_H
+
+#include <linux/errno.h>
+#include <linux/io.h>
+#include <time.h>
+
+/**
+ * readx_poll_timeout - Periodically poll an address until a condition is met or a timeout occurs
+ * @op: accessor function (takes @addr as its only argument)
+ * @addr: Address to poll
+ * @val: Variable to read the value into
+ * @cond: Break condition (usually involving @val)
+ * @timeout_us: Timeout in us, 0 means never timeout
+ *
+ * Returns 0 on success and -ETIMEDOUT upon a timeout. In either
+ * case, the last read value at @addr is stored in @val.
+ *
+ * When available, you'll probably want to use one of the specialized
+ * macros defined below rather than this macro directly.
+ */
+#define readx_poll_timeout(op, addr, val, cond, timeout_us)	\
+({ \
+	unsigned long timeout = timer_get_us() + timeout_us; \
+	for (;;) { \
+		(val) = op(addr); \
+		if (cond) \
+			break; \
+		if (timeout_us && time_after(timer_get_us(), timeout)) { \
+			(val) = op(addr); \
+			break; \
+		} \
+	} \
+	(cond) ? 0 : -ETIMEDOUT; \
+})
+
+
+#define readb_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readb, addr, val, cond, timeout_us)
+
+#define readw_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readw, addr, val, cond, timeout_us)
+
+#define readl_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readl, addr, val, cond, timeout_us)
+
+#define readq_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readq, addr, val, cond, timeout_us)
+
+#define readb_relaxed_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readb_relaxed, addr, val, cond, timeout_us)
+
+#define readw_relaxed_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readw_relaxed, addr, val, cond, timeout_us)
+
+#define readl_relaxed_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readl_relaxed, addr, val, cond, timeout_us)
+
+#define readq_relaxed_poll_timeout(addr, val, cond, timeout_us) \
+	readx_poll_timeout(readq_relaxed, addr, val, cond, timeout_us)
+
+#endif /* _LINUX_IOPOLL_H */