linux-kernel - [PATCH] iopoll: use fsleep() instead of usleep

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Message-Id: <20250626145119.2048423-1-jani.nikula@intel.com>
Date: Thu, 26 Jun 2025 17:51:19 +0300
From: Jani Nikula <jani.nikula@...el.com>
To: linux-kernel@...r.kernel.org
Cc: intel-gfx@...ts.freedesktop.org,
	jani.nikula@...el.com,
	Thomas Gleixner <tglx@...utronix.de>,
	Geert Uytterhoeven <geert+renesas@...der.be>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: [PATCH] iopoll: use fsleep() instead of usleep_range()

Sometimes it's necessary to poll with long sleeps, and the accuracy of
usleep_range() is overkill. Use the flexible sleep helper fsleep() for
sleeping in the read_poll_timeout() family of macros to automatically
choose the appropriate method of waiting.

Functionally there are a few consequences for existing users:

- 10 us and shorter sleeps will use usleep() instead of
  usleep_range(). Presumably this will not be an issue.

- When it leads to a slack of less than 25%, msleep() will be used
  instead of usleep_range(). Presumably this will not be an issue, given
  the sleeps will be longer in this case.

- Otherwise, the usleep_range() slack gets switched from the begin of
  the range to the end of the range, i.e. [sleep/2+1..sleep] ->
  [sleep..sleep+sleep/2]. In theory, this could be an issue in some
  cases, but difficult to determine before this hits the real world.

Signed-off-by: Jani Nikula <jani.nikula@...el.com>

---

Not really sure who to Cc, given MAINTAINERS doesn't match this. Adding
some past committers.

Cc: Thomas Gleixner <tglx@...utronix.de>
Cc: Geert Uytterhoeven <geert+renesas@...der.be>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc: linux-kernel@...r.kernel.org
---
 include/linux/iopoll.h | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/include/linux/iopoll.h b/include/linux/iopoll.h
index 91324c331a4b..359ff5ab95de 100644
--- a/include/linux/iopoll.h
+++ b/include/linux/iopoll.h
@@ -20,7 +20,7 @@
  * @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). Please
- *            read usleep_range() function description for details and
+ *            read fsleep() function description for details and
  *            limitations.
  * @timeout_us: Timeout in us, 0 means never timeout
  * @sleep_before_read: if it is true, sleep @sleep_us before read.
@@ -41,7 +41,7 @@
 	ktime_t __timeout = ktime_add_us(ktime_get(), __timeout_us); \
 	might_sleep_if((__sleep_us) != 0); \
 	if (sleep_before_read && __sleep_us) \
-		usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
+		fsleep(__sleep_us); \
 	for (;;) { \
 		(val) = op(args); \
 		if (cond) \
@@ -52,7 +52,7 @@
 			break; \
 		} \
 		if (__sleep_us) \
-			usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
+			fsleep(__sleep_us); \
 		cpu_relax(); \
 	} \
 	(cond) ? 0 : -ETIMEDOUT; \
@@ -120,7 +120,7 @@
  * @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). Please
- *            read usleep_range() function description for details and
+ *            read fsleep() function description for details and
  *            limitations.
  * @timeout_us: Timeout in us, 0 means never timeout
  *
-- 
2.39.5