[1/2] iopoll: Introduce memory-mapped IO polling macros

Commit Message

Mitchel Humpherys Sept. 11, 2014, 6:30 p.m. UTC

From: Matt Wagantall <[e-mail]>

It is sometimes necessary to poll a memory-mapped register until its
value satisfies some condition. Introduce a family of convenience macros
that do this. Tight-loop and sleeping versions are provided with and
without timeouts.

Cc: Thierry Reding <[e-mail]>
Cc: Will Deacon <[e-mail]>
Signed-off-by: Matt Wagantall <[e-mail]>
Signed-off-by: Mitchel Humpherys <[e-mail]>
---
 include/linux/iopoll.h | 114 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 114 insertions(+)
 create mode 100644 include/linux/iopoll.h

Comments

Will Deacon Sept. 22, 2014, 3:23 p.m. UTC | #1

Hi Mitch, Matt,

On Thu, Sep 11, 2014 at 07:30:43PM +0100, Mitchel Humpherys wrote:
> From: Matt Wagantall <[e-mail]>
> 
> It is sometimes necessary to poll a memory-mapped register until its
> value satisfies some condition. Introduce a family of convenience macros
> that do this. Tight-loop and sleeping versions are provided with and
> without timeouts.

[...]

> +/**
> + * readl_poll_timeout_noirq - Periodically poll an address until a condition is met or a timeout occurs
> + * @addr: Address to poll
> + * @val: Variable to read the value into
> + * @cond: Break condition (usually involving @val)
> + * @max_reads: Maximum number of reads before giving up
> + * @time_between_us: Time to udelay() between successive reads
> + *
> + * Returns 0 on success and -ETIMEDOUT upon a timeout.
> + */
> +#define readl_poll_timeout_noirq(addr, val, cond, max_reads, time_between_us) \
> +({ \
> +	int count; \
> +	for (count = (max_reads); count > 0; count--) { \
> +		(val) = readl(addr); \
> +		if (cond) \
> +			break; \
> +		udelay(time_between_us); \
> +	} \
> +	(cond) ? 0 : -ETIMEDOUT; \
> +})

I think I'd just name this one readl_poll_timeout_atomic, then drop the
helper macros you define later on. Drivers should be able to figure out the
parameters they want pretty easily and it makes it more explicit imo.

Anyway, the rest of the patch looks fine.

Will

Patch

diff --git a/include/linux/iopoll.h b/include/linux/iopoll.h
new file mode 100644
index 0000000000..8561881126
--- /dev/null
+++ b/include/linux/iopoll.h
@@ -0,0 +1,114 @@ 
+/*
+ * Copyright (c) 2012-2014 The Linux Foundation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 and
+ * only version 2 as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ */
+
+#ifndef _LINUX_IOPOLL_H
+#define _LINUX_IOPOLL_H
+
+#include <linux/kernel.h>
+#include <linux/types.h>
+#include <linux/hrtimer.h>
+#include <linux/delay.h>
+#include <linux/errno.h>
+#include <linux/io.h>
+
+/**
+ * readl_poll_timeout - Periodically poll an address until a condition is met or a timeout occurs
+ * @addr: Address to poll
+ * @val: Variable to read the value into
+ * @cond: Break condition (usually involving @val)
+ * @sleep_us: Maximum time to sleep between reads in us (0 tight-loops)
+ * @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. Must not
+ * be called from atomic context if sleep_us or timeout_us are used.
+ */
+#define readl_poll_timeout(addr, val, cond, sleep_us, timeout_us) \
+({ \
+	ktime_t timeout = ktime_add_us(ktime_get(), timeout_us); \
+	might_sleep_if(timeout_us); \
+	for (;;) { \
+		(val) = readl(addr); \
+		if (cond) \
+			break; \
+		if (timeout_us && ktime_compare(ktime_get(), timeout) > 0) { \
+			(val) = readl(addr); \
+			break; \
+		} \
+		if (sleep_us) \
+			usleep_range(DIV_ROUND_UP(sleep_us, 4), sleep_us); \
+	} \
+	(cond) ? 0 : -ETIMEDOUT; \
+})
+
+/**
+ * readl_poll_timeout_noirq - Periodically poll an address until a condition is met or a timeout occurs
+ * @addr: Address to poll
+ * @val: Variable to read the value into
+ * @cond: Break condition (usually involving @val)
+ * @max_reads: Maximum number of reads before giving up
+ * @time_between_us: Time to udelay() between successive reads
+ *
+ * Returns 0 on success and -ETIMEDOUT upon a timeout.
+ */
+#define readl_poll_timeout_noirq(addr, val, cond, max_reads, time_between_us) \
+({ \
+	int count; \
+	for (count = (max_reads); count > 0; count--) { \
+		(val) = readl(addr); \
+		if (cond) \
+			break; \
+		udelay(time_between_us); \
+	} \
+	(cond) ? 0 : -ETIMEDOUT; \
+})
+
+/**
+ * readl_poll - Periodically poll an address until a condition is met
+ * @addr: Address to poll
+ * @val: Variable to read the value into
+ * @cond: Break condition (usually involving @val)
+ * @sleep_us: Maximum time to sleep between reads in us (0 tight-loops)
+ *
+ * Must not be called from atomic context if sleep_us is used.
+ */
+#define readl_poll(addr, val, cond, sleep_us) \
+	readl_poll_timeout(addr, val, cond, sleep_us, 0)
+
+/**
+ * readl_tight_poll_timeout - Tight-loop on an address until a condition is met or a timeout occurs
+ * @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. Must not
+ * be called from atomic context if timeout_us is used.
+ */
+#define readl_tight_poll_timeout(addr, val, cond, timeout_us) \
+	readl_poll_timeout(addr, val, cond, 0, timeout_us)
+
+/**
+ * readl_tight_poll - Tight-loop on an address until a condition is met
+ * @addr: Address to poll
+ * @val: Variable to read the value into
+ * @cond: Break condition (usually involving @val)
+ *
+ * May be called from atomic context.
+ */
+#define readl_tight_poll(addr, val, cond) \
+	readl_poll_timeout(addr, val, cond, 0, 0)
+
+#endif /* _LINUX_IOPOLL_H */