linux-kernel - Re: [PATCH v2 10/15] checkpatch: Remove broken sleep/delay related checks

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Message-ID: <ZwZ6zsC_4X3OfGSQ@localhost.localdomain>
Date: Wed, 9 Oct 2024 14:45:02 +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>,
	Andy Whitcroft <apw@...onical.com>, Joe Perches <joe@...ches.com>,
	Dwaipayan Ray <dwaipayanray1@...il.com>
Subject: Re: [PATCH v2 10/15] checkpatch: Remove broken sleep/delay related
 checks

Le Wed, Sep 11, 2024 at 07:13:36AM +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 In all warnings the outdated documentation is referenced.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>