I had the same doubt the other day about the replacement of udelay() with usleep_range(). The corresponding range for the single argument value of udelay() is quite confusing as I couldn't decide the range.
But as much as I noticed checkpatch.pl gives warning for replacing udelay() with usleep_range() by checking the argument value of udelay(). In the documentation, it is written udelay() should be used for a sleep time of at most 10 microseconds but between 10 microseconds and 20 milliseconds, usleep_range() should be used.
I think the range is code specific and will depend on what range is acceptable and doesn't break the code.
Please correct me if I am wrong.
More clarification on this issue will be helpful.
On Sun, 29 Mar 2020, 15:17 Julia Lawall, <julia.lawall@xxxxxxxx> wrote:
On Sun, 29 Mar 2020, John Wyatt wrote:
> On Sun, 2020-03-29 at 11:28 +0200, Julia Lawall wrote:
> >
> > On Sun, 29 Mar 2020, John B. Wyatt IV wrote:
> >
> > > Fix style issue with usleep_range being reported as preferred over
> > > udelay.
> > >
> > > Issue reported by checkpatch.
> > >
> > > Please review.
> > >
> > > As written in Documentation/timers/timers-howto.rst udelay is the
> > > generally preferred API. hrtimers, as noted in the docs, may be too
> > > expensive for this short timer.
> > >
> > > Are the docs out of date, or, is this a checkpatch issue?
> > >
> > > Signed-off-by: John B. Wyatt IV <jbwyatt4@xxxxxxxxx>
> > > ---
> > > drivers/staging/fbtft/fb_agm1264k-fl.c | 2 +-
> > > 1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > b/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > index eeeeec97ad27..019c8cce6bab 100644
> > > --- a/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > +++ b/drivers/staging/fbtft/fb_agm1264k-fl.c
> > > @@ -85,7 +85,7 @@ static void reset(struct fbtft_par *par)
> > > dev_dbg(par->info->device, "%s()\n", __func__);
> > >
> > > gpiod_set_value(par->gpio.reset, 0);
> > > - udelay(20);
> > > + usleep_range(20, 20);
> >
> > usleep_range should have a range, eg usleep_range(50, 100);. But it
> > is
> > hard to know a priori what the range should be. So it is probably
> > better
> > to leave the code alone.
>
> Understood.
>
> With the question I wrote in the commit message:
>
> "As written in Documentation/timers/timers-howto.rst udelay is the
> generally preferred API. hrtimers, as noted in the docs, may be too
> expensive for this short timer.
>
> Are the docs out of date, or, is this a checkpatch issue?"
>
> Is usleep_range too expensive for this operation?
>
> Why does checkpatch favor usleep_range while the docs favor udelay?
I don't know the answer in detail, but it is quite possible that
checkpatch doesn't pay any attention to the delay argument. Checkpatch is
a perl script that highlights things that may be of concern. It is not a
precise static analsis tool.
As a matter of form, all of your Please review comments should have been
put below the ---. Currently, if someone had wanted to apply the patch,
you would make them do extra work to remove this information.
julia
>
> >
> > julia
> >
> > > gpiod_set_value(par->gpio.reset, 1);
> > > mdelay(120);
> > > }
> > > --
> > > 2.25.1
> > >
> > > --
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> > > https://groups.google.com/d/msgid/outreachy-kernel/20200329092204.770405-1-jbwyatt4%40gmail.com
> > > .
> > >
>
>
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