Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: [PATCH net-next 1/2] timer: add fsleep for flexible sleeping
From:   Heiner Kallweit <hkallweit1@gmail.com>
To:     Thomas Gleixner <tglx@linutronix.de>,
        Jonathan Corbet <corbet@lwn.net>,
        Realtek linux nic maintainers <nic_swsd@realtek.com>,
        David Miller <davem@davemloft.net>
Cc:     "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-doc@vger.kernel.org
References: <8e3c56ca-b43f-3877-0104-a1a279d5a6c5@gmail.com>
Message-ID: <5e3c3f78-344c-ae03-b6ae-ea55e402c1e7@gmail.com>
Date:   Fri, 1 May 2020 23:27:21 +0200
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.7.0
MIME-Version: 1.0
In-Reply-To: <8e3c56ca-b43f-3877-0104-a1a279d5a6c5@gmail.com>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Sleeping for a certain amount of time requires use of different
functions, depending on the time period.
Documentation/timers/timers-howto.rst explains when to use which
function, and also checkpatch checks for some potentially
problematic cases.

So let's create a helper that automatically chooses the appropriate
sleep function -> fsleep(), for flexible sleeping

If the delay is a constant, then the compiler should be able to ensure
that the new helper doesn't create overhead. If the delay is not
constant, then the new helper can save some code.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
---
 Documentation/timers/timers-howto.rst |  3 +++
 include/linux/delay.h                 | 11 +++++++++++
 2 files changed, 14 insertions(+)

diff --git a/Documentation/timers/timers-howto.rst b/Documentation/timers/timers-howto.rst
index 7e3167bec..afb0a43b8 100644
--- a/Documentation/timers/timers-howto.rst
+++ b/Documentation/timers/timers-howto.rst
@@ -110,3 +110,6 @@ NON-ATOMIC CONTEXT:
 			short, the difference is whether the sleep can be ended
 			early by a signal. In general, just use msleep unless
 			you know you have a need for the interruptible variant.
+
+	FLEXIBLE SLEEPING (any delay, uninterruptible)
+		* Use fsleep
diff --git a/include/linux/delay.h b/include/linux/delay.h
index 8e6828094..cb1d508ca 100644
--- a/include/linux/delay.h
+++ b/include/linux/delay.h
@@ -65,4 +65,15 @@ static inline void ssleep(unsigned int seconds)
 	msleep(seconds * 1000);
 }
 
+/* see Documentation/timers/timers-howto.rst for the thresholds */
+static inline void fsleep(unsigned long usecs)
+{
+	if (usecs <= 10)
+		udelay(usecs);
+	else if (usecs <= 20000)
+		usleep_range(usecs, 2 * usecs);
+	else
+		msleep(DIV_ROUND_UP(usecs, 1000));
+}
+
 #endif /* defined(_LINUX_DELAY_H) */
-- 
2.26.2