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

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Date:   Fri, 14 Aug 2020 12:31:46 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Crt Mori <cmo@...exis.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        linux-iio <linux-iio@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/5] iio:temperature:mlx90632: Convert polling while
 loop to do-while

On Fri, Aug 14, 2020 at 10:33 AM Crt Mori <cmo@...exis.com> wrote:
> On Thu, 13 Aug 2020 at 21:41, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > On Thu, Aug 13, 2020 at 4:04 PM Crt Mori <cmo@...exis.com> wrote:
> > > On Thu, 13 Aug 2020 at 13:24, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > > On Thu, Aug 13, 2020 at 2:14 PM Crt Mori <cmo@...exis.com> wrote:
> > > > > On Thu, 13 Aug 2020 at 13:03, Andy Shevchenko <andy.shevchenko@...il.com> wrote:
> > > > > > On Thu, Aug 13, 2020 at 10:53 AM Crt Mori <cmo@...exis.com> wrote:
> >
> > ...
> >
> > > > > > 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?
> > > >
> > >
> > > I tried and it did not work, so then I read the manual. Looking into
> > >
> > > * regmap_read_poll_timeout_atomic - Poll until a condition is met or a
> > > timeout occurs
> >
> > Why _atomic?!
>
> I just pasted something, it is the same as for non _atomic

OK.

...

> > >  * @delay_us: Time to udelay between reads in us (0 tight-loops).
> > >  *            Should be less than ~10us since udelay is used
> > >  *            (see Documentation/timers/timers-howto.rst).
> > >  * @timeout_us: Timeout in us, 0 means never timeout

...

> > > > > > >                 usleep_range(10000, 11000);
> >
> > You use here usleep_range(). The same is used for
> > regmap_read_poll_timeout(). What's the difference?
> >
> > Since it uses 1/4 of the range you probably need to update tries and
> > timeout_us to make it work.
> >
>
> Timeout_us here needs to be in one case 100 * 10ms (maybe not
> realistic as we could live with number of around 40 * 10ms), but this
> is a lot more than proposed range of usleep which Is up to 20ms. Even
> in best case this timeout should be 40 ms to give enough time to
> measure 2 channels for sure. So with the current timeout_us
> requirement we are outside of the range of the udelay timer and that
> is why I would need a macro with number of tries, not with the timeout
> value (or timeout value of ms).

I do not understand. The regmap_read_poll_timeout() is a macro which
unrolls in the very similar loop you have now in the code.
What prevents it from using it?

I think there is a big misunderstanding about the parameters of that macro.
delay_us (must be small enough), timeout_us can be any long.

-- 
With Best Regards,
Andy Shevchenko