[Outreachy kernel] [PATCH] staging: fbtft: Replace udelay with preferred usleep_range

[Soumyajit Deb]

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 at inria.fr> 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 Are the docs out of date, or, is this a checkpatch issue?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 at gmail.com>
> > > > ---
> > > >  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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