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SubjectRe: [PATCH v2] iio:dac:ti-dac7612: Add driver for Texas Instruments DAC7612
On Sat, 26 Jan 2019 22:34:50 +0100
Ricardo Ribalda Delgado <ricardo@ribalda.com> wrote:

> HI Jonathan
>
> Thanks for your review. I will make the changes and send it back to
> you after testing it on Monday on real hardware.
>
> Until then I have pushed my changes to
> https://github.com/ribalda/linux/tree/ribalda-iio-v3 in case you want
> to see it before I send it to the list.
> (I am still missing the dt-bindings)
>
> Some comments inline.
Replies inline.

>
> Best regards!
>
> On Sat, Jan 26, 2019 at 9:42 PM Jonathan Cameron <jic23@kernel.org> wrote:
> >
> > On Fri, 25 Jan 2019 11:00:55 +0100
> > Ricardo Ribalda Delgado <ricardo@ribalda.com> wrote:
> >
> > > It is a driver for Texas Instruments Dual, 12-Bit Serial Input
> > > Digital-to-Analog Converter.
> > >
> > > Datasheet of this chip:
> > > http://www.ti.com/lit/ds/sbas106/sbas106.pdf
> > >
> > > Signed-off-by: Ricardo Ribalda Delgado <ricardo@ribalda.com>
> > Hi Ricardo,
> >
> > Various bits and pieces inline.
> >
> > Jonathan
> >
> > > ---
> > >
> > > v2: Fix range
> > > MAINTAINERS | 6 ++
> > > drivers/iio/dac/Kconfig | 10 +++
> > > drivers/iio/dac/Makefile | 1 +
> > > drivers/iio/dac/ti-dac7612.c | 169 +++++++++++++++++++++++++++++++++++
> > > 4 files changed, 186 insertions(+)
> > > create mode 100644 drivers/iio/dac/ti-dac7612.c
> > >
> > > diff --git a/MAINTAINERS b/MAINTAINERS
> > > index d039f66a5cef..30ba5435906b 100644
> > > --- a/MAINTAINERS
> > > +++ b/MAINTAINERS
> > > @@ -14877,6 +14877,12 @@ F: Documentation/devicetree/bindings/clock/ti,sci-clk.txt
> > > F: drivers/clk/keystone/sci-clk.c
> > > F: drivers/reset/reset-ti-sci.c
> > >
> > > +Texas Instruments' DAC7612 DAC Driver
> > > +M: Ricardo Ribalda <ricardo@ribalda.com>
> > > +L: linux-iio@vger.kernel.org
> > > +S: Supported
> > > +F: drivers/iio/dac/ti-dac7612.c
> > > +
> > > THANKO'S RAREMONO AM/FM/SW RADIO RECEIVER USB DRIVER
> > > M: Hans Verkuil <hverkuil@xs4all.nl>
> > > L: linux-media@vger.kernel.org
> > > diff --git a/drivers/iio/dac/Kconfig b/drivers/iio/dac/Kconfig
> > > index f28daf67db6a..fbef9107acad 100644
> > > --- a/drivers/iio/dac/Kconfig
> > > +++ b/drivers/iio/dac/Kconfig
> > > @@ -375,6 +375,16 @@ config TI_DAC7311
> > >
> > > If compiled as a module, it will be called ti-dac7311.
> > >
> > > +config TI_DAC7612
> > > + tristate "Texas Instruments 12-bit 2-channel DAC driver"
> > > + depends on SPI_MASTER && GPIOLIB
> > > + help
> > > + Driver for the Texas Instruments DAC7612, DAC7612U, DAC7612UB
> > > + The driver hand drive the load pin automatically, otherwise
> > > + it needs to be toggled manually.
> >
> > Given the driver doesn't load without that pin, do we need to give
> > the otherwise? I would drop this comment entirely.
>
> I am probing the gpio with devm_gpiod_get_optional() so the driver can
> load without the pin
Hmm. I thought that would blow up when you tried to set the output but
it seems not as the gpiod function just returns without doing anything.

So is this a an actual usecase you have? My inclination would be to just
make it non optional otherwise. The thought of relying on a random pulse
from another device doesn't seem like a good idea to me.

>
> >
> > > +
> > > + If compiled as a module, it will be called ti-dac7612.
> > > +
> > > config VF610_DAC
> > > tristate "Vybrid vf610 DAC driver"
> > > depends on OF
> > > diff --git a/drivers/iio/dac/Makefile b/drivers/iio/dac/Makefile
> > > index f0a37c93de8e..1369fa1d2f0e 100644
> > > --- a/drivers/iio/dac/Makefile
> > > +++ b/drivers/iio/dac/Makefile
> > > @@ -41,4 +41,5 @@ obj-$(CONFIG_STM32_DAC) += stm32-dac.o
> > > obj-$(CONFIG_TI_DAC082S085) += ti-dac082s085.o
> > > obj-$(CONFIG_TI_DAC5571) += ti-dac5571.o
> > > obj-$(CONFIG_TI_DAC7311) += ti-dac7311.o
> > > +obj-$(CONFIG_TI_DAC7612) += ti-dac7612.o
> > > obj-$(CONFIG_VF610_DAC) += vf610_dac.o
> > > diff --git a/drivers/iio/dac/ti-dac7612.c b/drivers/iio/dac/ti-dac7612.c
> > > new file mode 100644
> > > index 000000000000..278406f69e0c
> > > --- /dev/null
> > > +++ b/drivers/iio/dac/ti-dac7612.c
> > > @@ -0,0 +1,169 @@
> > > +// SPDX-License-Identifier: GPL-2.0
> > > +/*
> > > + * DAC7612 Dual, 12-Bit Serial input Digital-to-Analog Converter
> > > + *
> > > + * Copyright 2019 Qtechnology A/S
> > > + * 2019 Ricardo Ribalda <ricardo@ribalda.com>
> > > + *
> > > + * Licensed under the GPL-2.
> > > + */
> > > +#include <linux/kernel.h>
> > > +#include <linux/module.h>
> > > +#include <linux/spi/spi.h>
> > > +#include <linux/gpio/consumer.h>
> > > +#include <linux/iio/iio.h>
> > > +
> > > +#define NUM_CHANS 2
> > > +#define RESOLUTION 12
> > Please prefix any naming that is generic like this with
> > the driver name. Avoids potential redefined clashes in the future.
> > Where they are 'real numbers' rather than Magic numbers I would
> > generally look at using the actual number rather than a define.
> >
> > > +
> > > +struct dac7612 {
> > > + struct spi_device *spi;
> > > + struct gpio_desc *nld;
> > > + uint16_t cache[NUM_CHANS];
> > > +};
> > > +
> > > +static int dac7612_cmd_single(struct dac7612 *priv, int channel, u16 val)
> > > +{
> > > + uint8_t buffer[2];
> > > + int ret;
> > > +
> > > + if (channel >= NUM_CHANS)
> > Is there any way this can happen? Seems a little over paranoid.
> > > + return -EINVAL;
> > > +
> > > + buffer[0] = BIT(5) | (channel << 4) | (val >> 8);
> > BIT(5) is a magic number so should probably come from a define
> > as should the shifts of the other parts.
> >
> > > + buffer[1] = val & 0xff;
> > > +
> > > + priv->cache[channel] = val;
> > > +
> > > + ret = spi_write(priv->spi, buffer, sizeof(buffer));
> >
> > spi write can potentially do a dma transfer so it needs
> > a dma safe buffer. This one isn't as it is on the stack.
> > Given it is a moderately fast path, best option is to put the
> > buffer in priv and use the __cacheline_aligned trick (plus the
> > fact private data is already cacheline aligned) to get it into
> > it's own cacheline. Wofram Sang's OSS talk on i2c dma is a good
> > tutorial on this and is on youtube if you have time.
> >
> > https://www.youtube.com/watch?v=JDwaMClvV-s
> >
> > > + if (ret)
> > > + return ret;
> > > +
> > > + gpiod_set_value(priv->nld, 0);
> > > + gpiod_set_value(priv->nld, 1);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +#define dac7612_CHANNEL(chan, name) { \
> > > + .type = IIO_VOLTAGE, \
> > > + .channel = (chan), \
> > > + .address = (chan), \
> > Not used, so don't set it.
> >
> > > + .indexed = true, \
> > These are bit fields, so whilst this works, = 1 is more conventional.
> >
> > > + .output = true, \
> > > + .datasheet_name = name, \
> > > + .info_mask_separate = BIT(IIO_CHAN_INFO_RAW), \
> > > + .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE), \
> > > + .scan_type = { \
> > > + .sign = 'u', \
> > > + .realbits = RESOLUTION, \
> > > + .storagebits = RESOLUTION, \
> > No need to provide scan_type as we don't have buffered output in
> > mainline. Also this would be wrong as storagebits needs to be
> > 8/16/32/64 etc.
> >
> > Would prefer a straight forward value like RESOLUTION was just
> > expressed as a number.
> >
> > > + }, \
> > > +}
> > > +
> > > +static const struct iio_chan_spec dac7612_channels[] = {
> > > + dac7612_CHANNEL(0, "OUTA"),
> > > + dac7612_CHANNEL(1, "OUTB"),
> > > +};
> > > +
> > > +static int dac7612_read_raw(struct iio_dev *iio_dev,
> > > + const struct iio_chan_spec *chan,
> > > + int *val, int *val2, long mask)
> > > +{
> > > + struct dac7612 *priv;
> > > +
> > > + switch (mask) {
> > > + case IIO_CHAN_INFO_RAW:
> > > + priv = iio_priv(iio_dev);
> > > + *val = priv->cache[chan->channel];
> > > + return IIO_VAL_INT;
> > > +
> > > + case IIO_CHAN_INFO_SCALE:
> > > + *val = 1000000;
> >
> > This makes me wonder. The units of voltage are millivolts, so is
> > raw value * 1000000 = value in mv?
>
> I tried using IIO_VAL_FRACTIONAL, with val = 1 and val2=1000000, and
> it only returned -EINVAL.

That is odd and definitely worth chasing down the reason.

> Then I discovered the PLUS_MICRO and I want to remember that cating
> the range sysfs file returned:
> 0,000001, but I will try again on Monday.
>
> >
> > That would make this a very high voltage device.
> > See Documentation/ABI/testing/sysfs-bus-iio* for
> > IIO ABI documentation.
> >
> > > + return IIO_VAL_INT_PLUS_MICRO;
> > > +
> > > + default:
> > > + return -EINVAL;
> > > + }
> > > +}
> > > +
> > > +static int dac7612_write_raw(struct iio_dev *iio_dev,
> > > + const struct iio_chan_spec *chan,
> > > + int val, int val2, long mask)
> > > +{
> > > + struct dac7612 *priv;
> >
> > struct dac7612 *priv = iio_priv(iio_dev);
> >
> > (it's just macro magic to get the right point so normally considered
> > fine to be called like this).
> >
> >
> > > + int ret;
> > > +
> > > + if (mask != IIO_CHAN_INFO_RAW)
> > > + return -EINVAL;
> > > +
> > > + if ((val >= BIT(RESOLUTION)) || val < 0)
> > > + return -EINVAL;
> >
> > As not providing a write_fmt function (which is fine)
> > should also sanity check that val2 is 0.
> >
> > > +
> > > + priv = iio_priv(iio_dev);
> > > + if (val == priv->cache[chan->channel])
> > > + return 0;
> > > +
> > > + mutex_lock(&iio_dev->mlock);
> > > + ret = dac7612_cmd_single(priv, chan->channel, val);
> > > + mutex_unlock(&iio_dev->mlock);
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static const struct iio_info dac7612_info = {
> > > + .read_raw = dac7612_read_raw,
> > > + .write_raw = dac7612_write_raw,
> > > +};
> > > +
> > > +static int dac7612_probe(struct spi_device *spi)
> > > +{
> > > + struct iio_dev *iio_dev;
> > > + struct dac7612 *priv;
> > > + int i;
> > > + int ret;
> > > +
> > > + iio_dev = devm_iio_device_alloc(&spi->dev, sizeof(*priv));
> > > + if (!iio_dev)
> > > + return -ENOMEM;
> > > +
> > > + priv = iio_priv(iio_dev);
> > > + priv->nld = devm_gpiod_get_optional(&spi->dev, "nLD", GPIOD_OUT_HIGH);
> >
> > This isn't a particularly standard gpio name. Hence this driver definitely
> > needs a DT binding doc (remember to cc dt list and maintainers). Also
> > this should almost certainly be prefixed with a vendor prefix.
> >
> > It's also not the name I'm seeing on the datasheet, so needs some justifying
> > comments.
> >
> > > + if (IS_ERR(priv->nld))
> > > + return PTR_ERR(priv->nld);
> > > + priv->spi = spi;
> > > + spi_set_drvdata(spi, iio_dev);
> > > + iio_dev->dev.parent = &spi->dev;
> > > + iio_dev->info = &dac7612_info;
> > > + iio_dev->modes = INDIO_DIRECT_MODE;
> > > + iio_dev->channels = dac7612_channels;
> > > + iio_dev->num_channels = NUM_CHANS;
> > ARRAY_SIZE.
> > > + iio_dev->name = spi_get_device_id(spi)->name;
> > > +
> > > + for (i = 0; i < NUM_CHANS; i++) {
> > ARRAY_SIZE
> > > + ret = dac7612_cmd_single(priv, i, 0);
> > > + if (ret)
> > > + return ret;
> > > + }
> > > +
> > > + return devm_iio_device_register(&spi->dev, iio_dev);
> > > +}
> > > +
> > > +static const struct spi_device_id dac7612_id[] = {
> > > + {"ti-dac7612"},
> > > + {}
> > > +};
> > > +MODULE_DEVICE_TABLE(spi, dac7612_id);
> > > +
> > > +static struct spi_driver dac7612_driver = {
> > > + .driver = {
> > > + .name = "ti-dac7612",
> > > + },
> > > + .probe = dac7612_probe,
> > > + .id_table = dac7612_id,
> > > +};
> > > +module_spi_driver(dac7612_driver);
> > > +
> > > +MODULE_AUTHOR("Ricardo Ribalda <ricardo@ribalda.com>");
> > > +MODULE_DESCRIPTION("Texas Instruments DAC7612 DAC driver");
> > > +MODULE_LICENSE("GPL v2");
> >
>
>

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