linux-kernel - Re: [PATCH v2 1/2] iio/adc: ingenic: Fix channel offsets in buffer

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Message-ID: <2fc0874ce8a802aeb98e553b15e27fb4d4b75a1c.camel@crapouillou.net>
Date:   Mon, 22 May 2023 12:23:43 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Artur Rojek <contact@...ur-rojek.eu>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Chris Morgan <macromorgan@...mail.com>,
        linux-mips@...r.kernel.org, linux-iio@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-input@...r.kernel.org
Subject: Re: [PATCH v2 1/2] iio/adc: ingenic: Fix channel offsets in buffer

Hi Andy,

Le lundi 22 mai 2023 à 13:18 +0300, Andy Shevchenko a écrit :
> On Mon, May 22, 2023 at 1:15 PM Andy Shevchenko
> <andy.shevchenko@...il.com> wrote:
> > On Mon, May 22, 2023 at 1:59 AM Artur Rojek
> > <contact@...ur-rojek.eu> wrote:
> 
> ...
> 
> > > +       u16 tdat[6];
> > > +       u32 val;
> > > +
> > > +       memset(tdat, 0, ARRAY_SIZE(tdat));
> > 
> > Yeah, as LKP tells us this should be sizeof() instead of
> > ARRAY_SIZE().
> > 
> > > +       for (i = 0; mask && i < ARRAY_SIZE(tdat); mask >>= 2) {
> > > +               if (mask & 0x3) {
> > 
> > (for the consistency it has to be GENMASK(), but see below)
> > 
> > First of all, strictly speaking we should use the full mask without
> > limiting it to the 0 element in the array (I'm talking about
> > active_scan_mask).
> > 
> > That said, we may actually use bit operations here in a better way,
> > i.e.
> > 
> >   unsigned long mask = active_scan_mask[0] & (active_scan_mask[0] -
> > 1);
> > 
> >   j = 0;
> >   for_each_set_bit(i, active_scan_mask, ...) {
> >     val = readl(...);
> >     /* Two channels per sample. Demux active. */
> >     tdat[j++] = val >> (16 * (i % 2));
> 
> Alternatively
> 
>      /* Two channels per sample. Demux active. */
>      if (i % 2)
>        tdat[j++] = upper_16_bits(val);
>      else
>        tdat[j++] = lower_16_bits(val);
> 
> which may be better to read.

It's not if/else though. You would check (i % 2) for the upper 16 bits,
and (i % 1) for the lower 16 bits. Both can be valid at the same time.

Cheers,
-Paul

> 
> >   }
> > 
> > > +                       val = readl(adc->base +
> > > JZ_ADC_REG_ADTCH);
> > > +                       /* Two channels per sample. Demux active.
> > > */
> > > +                       if (mask & BIT(0))
> > > +                               tdat[i++] = val & 0xffff;
> > > +                       if (mask & BIT(1))
> > > +                               tdat[i++] = val >> 16;
> > > +               }
> > >         }
> 
>