On 06/30, Jonathan Cameron wrote:
> On Sat, 29 Jun 2024 16:06:59 -0300
> Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx> wrote:
>
> > Add support for AD4000 series of low noise, low power, high speed,
> > successive approximation register (SAR) ADCs.
> >
> > Signed-off-by: Marcelo Schmitt <marcelo.schmitt@xxxxxxxxxx>
>
> Hi Marcelo
>
> A few comments inline. However, the spi_w8r8 etc can easily be a follow up
> optimization patch (if you agree it's a good improvement) and the
> other changes are so trivial I could tweak whilst applying.
>
...
> > + /*
> > + * The gain is stored as a fraction of 1000 and, as we need to
> > + * divide vref_mv by the gain, we invert the gain/1000 fraction.
> > + * Also multiply by an extra MILLI to preserve precision.
> > + * Thus, we have MILLI * MILLI equals MICRO as fraction numerator.
> > + */
> > + val = mult_frac(st->vref_mv, MICRO, st->gain_milli);
>
> If you are rolling a v7 for other reasons, stick some line breaks in here!
> It's a bit of a mass of text that is hard for my eyes to parse!
>
Ack
...
>
> > +static int ad4000_read_reg(struct ad4000_state *st, unsigned int *val)
> > +{
> > + struct spi_transfer t = {
> > + .tx_buf = st->tx_buf,
> > + .rx_buf = st->rx_buf,
> > + .len = 2,
> > + };
> > + int ret;
> > +
> > + st->tx_buf[0] = AD4000_READ_COMMAND;
> > + ret = spi_sync_transfer(st->spi, &t, 1);
> > + if (ret < 0)
> > + return ret;
> > +
> > + *val = st->rx_buf[1];
> > + return ret;
>
> I'd be tempted to do
>
> ssize_t ret;
>
> ret = spi_w8r8(AD4000_READ_COMMAND);
> if (ret < 0)
> return ret;
> *val = ret;
>
> return 0;
>
I tried this when working on v6. Only difference was I had declared ret as int.
Then reg values were not read correctly with spi_w8r8().
I'm either missing something or reg access must be 16-bit transfer.
Datasheet sais:
"The AD4000/AD4004/AD4008 configuration register is read from and written to
with a 16-bit SPI instruction."
Yet, besides possible delay between first and last 8 SCLK pulses, I don't see
any transfer level differences between current and spi_w8r8() versions.
>
>
...
> > + ret = ad4000_write_reg(st, reg_val);
> > + if (ret < 0)
> > + return ret;
> > +
> > + st->span_comp = span_comp_en;
> > + return ret;
>
> If you are spinning for another reason, make it clear this is always good.
> The spi_write() never returns positive so current code is correct but I had
> to go check which this would have avoided.
>
> return 0;
Ack
>
> If nothing else comes up, I'll probably tweak whilst applying.
>
> J
>
> > + }
> > + unreachable();
> > + default:
> > + return -EINVAL;
> > + }
> > +}
>
