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Message-ID: <ngcbj6p7vfakah5fqsxqjlmrcycpg5rxfrbh4s34fll2kb3zq2@eyesluawn5w2>
Date: Thu, 7 Aug 2025 14:10:01 +0100
From: Nuno Sá <noname.nuno@...il.com>
To: Matti Vaittinen <mazziesaccount@...il.com>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
Lars-Peter Clausen <lars@...afoo.de>, Michael Hennerich <Michael.Hennerich@...log.com>,
Jonathan Cameron <jic23@...nel.org>, David Lechner <dlechner@...libre.com>,
Nuno Sá <nuno.sa@...log.com>, Andy Shevchenko <andy@...nel.org>, Rob Herring <robh@...nel.org>,
Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley <conor+dt@...nel.org>,
Liam Girdwood <lgirdwood@...il.com>, Mark Brown <broonie@...nel.org>, linux-iio@...r.kernel.org,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 06/10] iio: adc: ad7476: Drop convstart chan_spec
On Thu, Aug 07, 2025 at 01:41:31PM +0100, Nuno Sá wrote:
> On Thu, Aug 07, 2025 at 12:34:52PM +0300, Matti Vaittinen wrote:
> > The ad7476 driver defines separate chan_spec structures for operation
> > with and without convstart GPIO. At quick glance this may seem as if the
> > driver did provide more than 1 data-channel to users - one for the
> > regular data, other for the data obtained with the convstart GPIO.
> >
> > The only difference between the 'convstart' and 'non convstart'
> > -channels is presence / absence of the BIT(IIO_CHAN_INFO_RAW) in
> > channel's flags.
> >
> > We can drop the convstart channel spec, and related convstart macro, by
> > allocating a mutable per driver instance channel spec an adding the flag
> > in probe if needed. This will simplify the driver with the cost of added
> > memory consumption.
> >
> > Assuming there aren't systems with very many ADCs and very few
> > resources, this tradeoff seems worth making.
> >
> > Simplify the driver by dropping the 'convstart' channel spec and
> > allocating the chan spec for each driver instance.
>
> I do not agree with this one. Looking at the diff, code does not look
> simpler to me...
Ok, on a second thought I'm ok with this. It makes adding devices easier
and (IIUC) for the one you're adding later we only have "convst_channel"
channels.
On comment though...
>
> - Nuno Sá
>
> >
> > Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> >
> > ---
> > Revision history:
> > v1 => v2:
> > - New patch
> >
> > I considered squashing this change with the one limiting the chip_info
> > scope. Having this as a separate change should help reverting if someone
> > complains about the increased memory consumption though.
> > ---
> > drivers/iio/adc/ad7476.c | 31 ++++++++++++++++++-------------
> > 1 file changed, 18 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/iio/adc/ad7476.c b/drivers/iio/adc/ad7476.c
> > index e97742912b8e..a30eb016c11c 100644
> > --- a/drivers/iio/adc/ad7476.c
> > +++ b/drivers/iio/adc/ad7476.c
> > @@ -29,8 +29,6 @@ struct ad7476_state;
> > struct ad7476_chip_info {
> > unsigned int int_vref_mv;
> > struct iio_chan_spec channel[2];
> > - /* channels used when convst gpio is defined */
> > - struct iio_chan_spec convst_channel[2];
> > void (*reset)(struct ad7476_state *);
> > bool has_vref;
> > bool has_vdrive;
> > @@ -41,6 +39,7 @@ struct ad7476_state {
> > struct gpio_desc *convst_gpio;
> > struct spi_transfer xfer;
> > struct spi_message msg;
> > + struct iio_chan_spec channel[2];
> > int scale_mv;
> > /*
> > * DMA (thus cache coherency maintenance) may require the
> > @@ -153,24 +152,18 @@ static int ad7476_read_raw(struct iio_dev *indio_dev,
> > #define AD7940_CHAN(bits) _AD7476_CHAN((bits), 15 - (bits), \
> > BIT(IIO_CHAN_INFO_RAW))
> > #define AD7091R_CHAN(bits) _AD7476_CHAN((bits), 16 - (bits), 0)
> > -#define AD7091R_CONVST_CHAN(bits) _AD7476_CHAN((bits), 16 - (bits), \
> > - BIT(IIO_CHAN_INFO_RAW))
> > #define ADS786X_CHAN(bits) _AD7476_CHAN((bits), 12 - (bits), \
> > BIT(IIO_CHAN_INFO_RAW))
> >
> > static const struct ad7476_chip_info ad7091_chip_info = {
> > .channel[0] = AD7091R_CHAN(12),
> > .channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> > - .convst_channel[0] = AD7091R_CONVST_CHAN(12),
> > - .convst_channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> > .reset = ad7091_reset,
> > };
> >
> > static const struct ad7476_chip_info ad7091r_chip_info = {
> > .channel[0] = AD7091R_CHAN(12),
> > .channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> > - .convst_channel[0] = AD7091R_CONVST_CHAN(12),
> > - .convst_channel[1] = IIO_CHAN_SOFT_TIMESTAMP(1),
> > .int_vref_mv = 2500,
> > .has_vref = true,
> > .reset = ad7091_reset,
> > @@ -282,7 +275,7 @@ static int ad7476_probe(struct spi_device *spi)
> > const struct ad7476_chip_info *chip_info;
> > struct ad7476_state *st;
> > struct iio_dev *indio_dev;
> > - int ret;
> > + int ret, i;
> >
> > indio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*st));
> > if (!indio_dev)
> > @@ -332,16 +325,28 @@ static int ad7476_probe(struct spi_device *spi)
> > if (IS_ERR(st->convst_gpio))
> > return PTR_ERR(st->convst_gpio);
> >
> > + /*
> > + * This will never realize. Unless someone changes the channel specs
> > + * in this driver. And if someone does, without changing the loop
> > + * below, then we'd better immediately produce a big fat error, before
> > + * the change proceeds from that developer's table.
> > + */
> > + BUILD_BUG_ON(ARRAY_SIZE(st->channel) != ARRAY_SIZE(chip_info->channel));
I guess it make sense but still looks too fancy for this :)
> > + for (i = 0; i < ARRAY_SIZE(st->channel); i++) {
> > + st->channel[i] = chip_info->channel[i];
> > + if (st->convst_gpio)
I would flip this an do:
if (!st->convst_gpio)
break;
> > + st->channel[i].info_mask_separate |=
> > + BIT(IIO_CHAN_INFO_RAW);
__set_bit()...
- Nuno Sá
> > + }
> > +
> > st->spi = spi;
> >
> > indio_dev->name = spi_get_device_id(spi)->name;
> > indio_dev->modes = INDIO_DIRECT_MODE;
> > - indio_dev->channels = chip_info->channel;
> > - indio_dev->num_channels = 2;
> > + indio_dev->channels = st->channel;
> > + indio_dev->num_channels = ARRAY_SIZE(st->channel);
> > indio_dev->info = &ad7476_info;
> >
> > - if (st->convst_gpio)
> > - indio_dev->channels = chip_info->convst_channel;
> > /* Setup default message */
> >
> > st->xfer.rx_buf = &st->data;
> > --
> > 2.50.1
> >
>
>
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