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

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Message-ID: <9812499a8e017b8e01327069c8063e5f213bb1c8.camel@crapouillou.net>
Date:   Mon, 22 May 2023 12:20:42 +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,

Le lundi 22 mai 2023 à 13:15 +0300, Andy Shevchenko a écrit :
> On Mon, May 22, 2023 at 1:59 AM Artur Rojek <contact@...ur-rojek.eu>
> wrote:
> > 
> > Consumers expect the buffer to only contain enabled channels. While
> > preparing the buffer, the driver makes two mistakes:
> > 1) It inserts empty data for disabled channels.
> > 2) Each ADC readout contains samples for two 16-bit channels. If
> > either
> >    of them is active, the whole 32-bit sample is pushed into the
> > buffer
> >    as-is.
> > 
> > Both of those issues cause the active channels to appear at the
> > wrong
> > offsets in the buffer. Fix the above by demuxing samples for active
> > channels only.
> > 
> > This has remained unnoticed, as all the consumers so far were only
> > using
> > channels 0 and 1, leaving them unaffected by changes introduced in
> > this
> > commit.
> 
> ...
> 
> > +       u16 tdat[6];
> > +       u32 val;
> > +
> > +       memset(tdat, 0, ARRAY_SIZE(tdat));
> 
> Yeah, as LKP tells us this should be sizeof() instead of
> ARRAY_SIZE().

Probably "u16 tdat[6] = { 0 };" would work too?

Cheers,
-Paul

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