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

[Paul Cercueil]

Hi Andy,

Le lundi 22 mai 2023 à 14:05 +0300, Andy Shevchenko a écrit :
> On Mon, May 22, 2023 at 1:23 PM Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> wrote:
> > 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@xxxxxxxxx> wrote:
> > > > On Mon, May 22, 2023 at 1:59 AM Artur Rojek
> > > > <contact@xxxxxxxxxxxxxx> 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.
> 
> Are you sure? Have you looked into the proposed code carefully?

Yes. I co-wrote the original code, I know what it's supposed to do.

> 
> What probably can be done differently is the read part, that can be
> called once. But looking at it I'm not sure how it's supposed to work
> at all, since the address is always the same. How does the code and
> hardware are in sync with the channels?

It's a FIFO.

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