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Message-ID: <ZxJVKEouOke_sbd9@localhost.localdomain>
Date: Fri, 18 Oct 2024 14:31:36 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Anna-Maria Behnsen <anna-maria@...utronix.de>
Cc: Thomas Gleixner <tglx@...utronix.de>, Jonathan Corbet <corbet@....net>,
linux-kernel@...r.kernel.org, Len Brown <len.brown@...el.com>,
"Rafael J . Wysocki" <rafael@...nel.org>,
rust-for-linux@...r.kernel.org, Alice Ryhl <aliceryhl@...gle.com>,
FUJITA Tomonori <fujita.tomonori@...il.com>,
Andrew Lunn <andrew@...n.ch>, Miguel Ojeda <ojeda@...nel.org>,
Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>,
Dwaipayan Ray <dwaipayanray1@...il.com>
Subject: Re: [PATCH v4] checkpatch: Remove broken sleep/delay related checks
Le Wed, Oct 16, 2024 at 12:05:31PM +0200, Anna-Maria Behnsen a écrit :
> checkpatch.pl checks for several things related to sleep and delay
> functions. In all warnings the outdated documentation is referenced. All
> broken parts are listed one by one in the following with an explanation why
> this check is broken. For a basic background of those functions please also
> refere to the updated function descriptions of udelay(), nsleep_range() and
> msleep().
>
> Be aware: The change is done with a perl knowledge of the level "I'm able
> to spell perl".
>
> The following checks are broken:
>
> - Check: (! ($delay < 10) )
> Message: "usleep_range is preferred over udelay;
> see Documentation/timers/timers-howto.rst\n"
> Why is the check broken: When it is an atomic context, udelay() is
> mandatory.
>
> - Check: ($min eq $max)
> Message: "usleep_range should not use min == max args;
> see Documentation/timers/timers-howto.rst\n"
> Why is the check broken: When the requested accuracy for the sleep
> duration requires it, it is also valid to use
> min == max.
>
> - Check: ($delay > 2000)
> Message: "long udelay - prefer mdelay;
> see arch/arm/include/asm/delay.h\n"
> Why is the check broken: The threshold when to start using mdelay() to
> prevent an overflow depends on
> MAX_UDELAY_MS. This value is architecture
> dependent. The used value for the check and
> reference is arm specific. Generic would be 5ms,
> but this would "break" arm, loongarch and mips
> and also the arm value might "break" mips and
> loongarch in some configurations.
>
> - Check: ($1 < 20)
> Message: "msleep < 20ms can sleep for up to 20ms;
> see Documentation/timers/timers-howto.rst\n"
> Why is the check broken: msleep(1) might sleep up to 20ms but only on a
> HZ=100 system. On a HZ=1000 system this will be
> 2ms. This means, the threshold cannot be hard
> coded as it depends on HZ (jiffy granularity and
> timer wheel bucket/level granularity) and also
> on the required accuracy of the callsite. See
> msleep() and also the USLEEP_RANGE_UPPER_BOUND
> value.
>
> Remove all broken checks. Update checkpatch documentation accordingly.
>
> Cc: Andy Whitcroft <apw@...onical.com>
> Cc: Joe Perches <joe@...ches.com>
> Cc: Dwaipayan Ray <dwaipayanray1@...il.com>
> Signed-off-by: Anna-Maria Behnsen <anna-maria@...utronix.de>
Acked-by: Frederic Weisbecker <frederic@...nel.org>
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