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

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Message-ID: <CAHp75VedgVOA4qTJFeVuabKXBaB=y4Ss0fLu7a7J9GGgWFPqQg@mail.gmail.com>
Date:   Mon, 22 May 2023 13:18:08 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Artur Rojek <contact@...ur-rojek.eu>
Cc:     Paul Cercueil <paul@...pouillou.net>,
        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

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.

>   }
>
> > +                       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;
> > +               }
> >         }


-- 
With Best Regards,
Andy Shevchenko