Re: [PATCH v5 3/5] iio:temperature:mlx90632: Convert polling while loop to do-while

From: Andy Shevchenko <andy.shevchenko@gmail.com>
To: Crt Mori <cmo@melexis.com>
Cc: Jonathan Cameron <jic23@kernel.org>,
	linux-iio <linux-iio@vger.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v5 3/5] iio:temperature:mlx90632: Convert polling while loop to do-while
Date: Thu, 13 Aug 2020 14:24:23 +0300	[thread overview]
Message-ID: <CAHp75Vd+3SopKog6uhSKoOLn+tECsQfs7kRbJsrMZEbNRpk8bQ@mail.gmail.com> (raw)
In-Reply-To: <CAKv63uv=b60B9RXBJF4HEhMOowu-qbGrv7LsmJVvkkERSida-A@mail.gmail.com>

On Thu, Aug 13, 2020 at 2:14 PM Crt Mori <cmo@melexis.com> wrote:
>
> On Thu, 13 Aug 2020 at 13:03, Andy Shevchenko <andy.shevchenko@gmail.com> wrote:
> >
> > On Thu, Aug 13, 2020 at 10:53 AM Crt Mori <cmo@melexis.com> wrote:
> > >
> > > Reduce number of lines and improve readability to convert polling while
> > > loops to do-while. The iopoll.h interface was not used, because we
> > > require more than 20ms timeout, because time for sensor to perform a
> > > measurement is around 10ms and it needs to perform measurements for each
> > > channel (which currently is 3).
> >
> > I don't see how it prevents using iopoll.h. It uses usleep_range()
> > under the hood in the same way you did here, but open coded.
> >
>
> One loop is indeed 10ms and that is not the problem, the problem is
> that timeout is at least 3 calls of this data ready (3 channels), so
> that is at minimum 30ms of timeout, or it could even be 4 in worse
> case scenario and that is outside of the range for usleep to measure.
> So in case of the other loop, where we wait 200ms for channel refresh
> it is also out of scope. Timeout should be in number of tries or in
> msleep range if you ask me.

I still didn't buy it. You have in both cases usleep_range(). Why in
your case it's okay and in regmap_read_poll_timeout() is not?

> > ...
> >
> > > -       while (tries-- > 0) {
> > > +       do {
> > >                 ret = regmap_read(data->regmap, MLX90632_REG_STATUS,
> > >                                   &reg_status);
> > >                 if (ret < 0)
> > >                         return ret;
> > > -               if (reg_status & MLX90632_STAT_DATA_RDY)
> > > -                       break;
> > >                 usleep_range(10000, 11000);
> > > -       }
> > > +       } while (!(reg_status & MLX90632_STAT_DATA_RDY) && tries--);
> > >
> > >         if (tries < 0) {
> > >                 dev_err(&data->client->dev, "data not ready");

-- 
With Best Regards,
Andy Shevchenko