Re: [PATCH] iio: adc: ad4000: Avoid potential double data word read

[Andy Shevchenko]

On Wed, Apr 16, 2025 at 12:22 AM David Lechner <dlechner@xxxxxxxxxxxx> wrote:
> On 4/15/25 1:02 PM, Andy Shevchenko wrote:
> > On Tue, Apr 15, 2025 at 3:21 PM Marcelo Schmitt
> > <marcelo.schmitt@xxxxxxxxxx> wrote:

...

> >>         xfers[1].rx_buf = &st->scan.data;
> >> -       xfers[1].len = BITS_TO_BYTES(chan->scan_type.storagebits);
> >> +       xfers[1].len = chan->scan_type.realbits > 16 ? 4 : 2;
> >
> > But wouldn't be logical to have
> >
> >        xfers[1].len = BITS_TO_BYTES(chan->scan_type.realbits);
> >
> > ?
>
> No, SPI expects 1, 2 or 4 bytes, never 3. If realbits is 18, we
> need len = 4.
>
> It would have to be:
>
>         xfers[1].len = roundup_pow_of_two(BITS_TO_BYTES(chan->scan_type.realbits));
>
> But that gets too long for 1 line

Actually there are a handful of drivers including SPI core that need
that helper already, I would prefer to have a helper defined in spi.h.

, so I prefer what Marcelo wrote.
>
> Maybe an idea for another day:
>
> #define SPI_LEN_FOR_BITS(bits) roundup_pow_of_two(BITS_TO_BYTES(bits))

Right, but as static inline to have stricter types.

> There are a couple of places in spi/ that could use this and several
> iio drivers.

-- 
With Best Regards,
Andy Shevchenko