Re: [PATCH v5 10/10] iio: accel: adxl345: add FIFO with watermark events

Lothar Rubusch
2024-12-10T21:55:17Z

Hi Jonathan,
Find my answers down below.
Best,
L

On Sun, Dec 8, 2024 at 5:34 PM Jonathan Cameron <jic23@kernel.org> wrote:
>
> On Thu, 5 Dec 2024 17:13:43 +0000
> Lothar Rubusch <l.rubusch@gmail.com> wrote:
>
> > Add a basic setup for FIFO with configurable watermark. Add a handler
> > for watermark interrupt events and extend the channel for the
> > scan_index needed for the iio channel. The sensor is configurable to use
> > a FIFO_BYPASSED mode or a FIFO_STREAM mode. For the FIFO_STREAM mode now
> > a watermark can be configured, or disabled by setting 0. Further features
> > require a working FIFO setup.
> >
> > Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
> Various comments inline.
>
> Thanks,
>
> Jonathan
>
> > ---
> > drivers/iio/accel/adxl345_core.c | 300 +++++++++++++++++++++++++++++++
> > 1 file changed, 300 insertions(+)
> >
> > diff --git a/drivers/iio/accel/adxl345_core.c b/drivers/iio/accel/adxl345_core.c
> > index 3067a70c54e..58ed82d66dc 100644
> > --- a/drivers/iio/accel/adxl345_core.c
> > +++ b/drivers/iio/accel/adxl345_core.c
> > @@ -15,15 +15,28 @@
> >
> > #include <linux/iio/iio.h>
> > #include <linux/iio/sysfs.h>
> > +#include <linux/iio/buffer.h>
> > +#include <linux/iio/events.h>
>
> I'm not seeing any use of this header yet. Bring it in when you need it.
>
> > +#include <linux/iio/kfifo_buf.h>
> >
> > #include "adxl345.h"
> >
> > +#define ADXL345_FIFO_BYPASS 0
> > +#define ADXL345_FIFO_FIFO 1
> > +#define ADXL345_FIFO_STREAM 2
> > +
> > +#define ADXL345_DIRS 3
> > +
> > struct adxl345_state {
> > int irq;
> > const struct adxl345_chip_info *info;
> > struct regmap *regmap;
> > + __le16 fifo_buf[ADXL345_DIRS * ADXL345_FIFO_SIZE];
> > bool fifo_delay; /* delay: delay is needed for SPI */
> > u8 intio;
> > + u8 int_map;
> > + u8 watermark;
> > + u8 fifo_mode;
> > };
> >
> > #define ADXL345_CHANNEL(index, reg, axis) { \
> > @@ -36,6 +49,13 @@ struct adxl345_state {
> > .info_mask_shared_by_type = BIT(IIO_CHAN_INFO_SCALE) | \
> > BIT(IIO_CHAN_INFO_SAMP_FREQ), \
> > .scan_index = (index), \
> > + .scan_type = { \
> > + .sign = 's', \
> > + .realbits = 13, \
> > + .storagebits = 16, \
> > + .shift = 0, \
>
> No need to specify shift of 0. It's the 'obvious' default and C will set it to 0
> for you anyway.
>
> > + .endianness = IIO_LE, \
> > + }, \
> > }
> >
> > enum adxl345_chans {
> > @@ -48,6 +68,25 @@ static const struct iio_chan_spec adxl345_channels[] = {
> > ADXL345_CHANNEL(2, chan_z, Z),
> > };
> >
> > +static int adxl345_set_interrupts(struct adxl345_state *st)
> > +{
> > + int ret;
> > + unsigned int int_enable = st->int_map;
> > + unsigned int int_map;
> > +
> > + /* Any bits set to 0 in the INT map register send their respective
>
> /*
> * Any bits....
>
>
> > + * interrupts to the INT1 pin, whereas bits set to 1 send their respective
> > + * interrupts to the INT2 pin. The intio shall convert this accordingly.
> > + */
> > + int_map = 0xFF & (st->intio ? st->int_map : ~st->int_map);
> > +
> > + ret = regmap_write(st->regmap, ADXL345_REG_INT_MAP, int_map);
> > + if (ret)
> > + return ret;
> > +
> > + return regmap_write(st->regmap, ADXL345_REG_INT_ENABLE, int_enable);
> > +}
>
>
> > +/**
> > + * adxl345_get_samples() - Read number of FIFO entries.
> > + * @st: The initialized state instance of this driver.
> > + *
> > + * The sensor does not support treating any axis individually, or exclude them
> > + * from measuring.
> > + *
> > + * Return: negative error, or value.
> > + */
> > +static int adxl345_get_samples(struct adxl345_state *st)
> > +{
> > + unsigned int regval = 0;
> > + int ret;
> > +
> > + ret = regmap_read(st->regmap, ADXL345_REG_FIFO_STATUS, &regval);
> > + if (ret < 0)
> > + return ret;
> > +
> > + return 0x3f & regval;
> FIELD_GET() for all stuff like this with appropriate #define for the mask.
>
> > +}
> > +
> > +/**
> > + * adxl345_fifo_transfer() - Read samples number of elements.
> > + * @st: The instance of the state object of this sensor.
> > + * @samples: The number of lines in the FIFO referred to as fifo_entry,
> > + * a fifo_entry has 3 elements for X, Y and Z direction of 2 bytes each.
> > + *
> > + * It is recommended that a multiple-byte read of all registers be performed to
> > + * prevent a change in data between reads of sequential registers. That is to
> > + * read out the data registers X0, X1, Y0, Y1, Z0, Z1 at once.
>
> Doesn't match the code which is reading just one register lots of times.

This is one of my painpoints, regmap_noinc_read() worked here, for a
linewise reading of FIFO elements. Say, I could read X0, X1, Y0,... Z1
in one command. Also, I tried here regmap_bulk_read(). At all, I find
this solution is working, but I'm not sure if there is not a total
differnt way to do the read out.

> > + *
> > + * Return: 0 or error value.
> > + */
> > +static int adxl345_fifo_transfer(struct adxl345_state *st, int samples)
> > +{
> > + size_t count;
> > + int i, ret;
> > +
> > + count = sizeof(st->fifo_buf[0]) * ADXL345_DIRS;
> > + for (i = 0; i < samples; i++) {
> > + ret = regmap_noinc_read(st->regmap, ADXL345_REG_XYZ_BASE,
> > + st->fifo_buf + (i * count / 2), count);
> > + if (ret < 0)
> > + return ret;
>
> This is where I'd expect to see the delay mentioned below.

I agree with the delay, I'll move it.

> > + }
> > + return ret;
> > +}
> > +
>
> > +static int adxl345_buffer_predisable(struct iio_dev *indio_dev)
> > +{
> > + struct adxl345_state *st = iio_priv(indio_dev);
> > + int ret;
> > +
> > + st->int_map = 0x00;
> > +
> > + ret = adxl345_set_interrupts(st);
> > + if (ret < 0)
> > + return ret;
> > +
> > + st->fifo_mode = ADXL345_FIFO_BYPASS;
> > + return adxl345_set_fifo(st);
> I'd normally expect order in predisable to be reverse of that in postenable.
> Why isn't it? That is why is the set_fifo here after set_interrupts and
> not before it. Add a comment.
>
> > +}
> > +
> > +static const struct iio_buffer_setup_ops adxl345_buffer_ops = {
> > + .postenable = adxl345_buffer_postenable,
> > + .predisable = adxl345_buffer_predisable,
> > +};
> > +
> > +static int adxl345_get_status(struct adxl345_state *st)
> > +{
> > + int ret;
> > + unsigned int regval;
> > +
> > + ret = regmap_read(st->regmap, ADXL345_REG_INT_SOURCE, &regval);
> > + if (ret < 0)
> > + return ret;
> > +
> > + return (0xff & regval);
>
> No brackets needed.
>
> > +}
> > +
> > +static int adxl345_fifo_push(struct iio_dev *indio_dev,
> > + int samples)
> > +{
> > + struct adxl345_state *st = iio_priv(indio_dev);
> > + int i, ret;
> > +
> > + if (samples <= 0)
> > + return -EINVAL;
> > +
> > + ret = adxl345_fifo_transfer(st, samples);
> > + if (ret)
> > + return ret;
> > +
> > + for (i = 0; i < ADXL345_DIRS * samples; i += ADXL345_DIRS) {
> > + /*
> > + * To ensure that the FIFO has completely popped, there must be at least 5
> > + * us between the end of reading the data registers, signified by the
> > + * transition to register 0x38 from 0x37 or the CS pin going high, and the
> > + * start of new reads of the FIFO or reading the FIFO_STATUS register. For
> > + * SPI operation at 1.5 MHz or lower, the register addressing portion of the
> > + * transmission is sufficient delay to ensure the FIFO has completely
> > + * popped. It is necessary for SPI operation greater than 1.5 MHz to
> > + * de-assert the CS pin to ensure a total of 5 us, which is at most 3.4 us
> > + * at 5 MHz operation.
> > + */
> > + if (st->fifo_delay && (samples > 1))
> > + udelay(3);
>
> I'm not following why a delay here helps. At this point you're read masses of
> data from the fifo without the delays you mention.
>
> > +
> > + iio_push_to_buffers(indio_dev, &st->fifo_buf[i]);
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +/**
> > + * adxl345_event_handler() - Handle events of the ADXL345.
>
> Up to you but...
> Given it's an IIO driver and that we have a very specific meaning
> for events, maybe just call this adxl345_irq_handler()?
>
> > + * @irq: The irq being handled.
> > + * @p: The struct iio_device pointer for the device.
> > + *
> > + * Return: The interrupt was handled.
> > + */
> > +static irqreturn_t adxl345_event_handler(int irq, void *p)
> > +{
> > + struct iio_dev *indio_dev = p;
> > + struct adxl345_state *st = iio_priv(indio_dev);
> > + u8 int_stat;
> > + int samples;
> > +
> > + int_stat = adxl345_get_status(st);
> > + if (int_stat < 0)
> > + return IRQ_NONE;
> > +
> > + if (int_stat == 0x0)
> Doesn't this correspond to 'not our interrupt'?
> If that's the case return IRQ_NONE is the right way to go and not reset the
> interrupt. You have registered it as maybe shared, and if it is, then this
> is a common thing to happen as interrupt from another device.
>

Here I see actually
+ int_stat = adxl345_get_status(st);
+ if (int_stat < 0)
+ return IRQ_NONE; // a bus error, reading register not possible
...and then...
+ if (int_stat == 0x0)
+ // interrupt sources were 0, so IRQ not from our sensor

I'm unsure if the first IRQ_NONE here is actually correct. I mean, if
the bus is not working,
actually any IRQ usage should be considered broken. Is there a way to
break out of measuring?

> > + goto err;
> > +
> > + if (int_stat & ADXL345_INT_OVERRUN)
> > + goto err;
> > +
> > + if (int_stat & (ADXL345_INT_DATA_READY | ADXL345_INT_WATERMARK)) {
>
> I think you only ever enable the INT_WATERMARK? If so does it
> make sense to check for DATA_READY as well?
>

Watermark comes usually with data ready or overrun. I guess for the
FIFO watermark, just evaluating watermark is probably sufficient. For
other events, it then might be notification w/ a data ready set.
Probably better to introduce data ready when it's actually really
needed?

> > + samples = adxl345_get_samples(st);
> > + if (samples < 0)
> > + goto err;
> > +
> > + if (adxl345_fifo_push(indio_dev, samples) < 0)
> > + goto err;
> > +
> > + }
> > + return IRQ_HANDLED;
> > +
> > +err:
> > + adxl345_fifo_reset(st);
> > +
> > + return IRQ_HANDLED;
> > +}
> > +
> > static const struct iio_info adxl345_info = {
> > .attrs = &adxl345_attrs_group,
> > .read_raw = adxl345_read_raw,
> > .write_raw = adxl345_write_raw,
> > .write_raw_get_fmt = adxl345_write_raw_get_fmt,
> > + .hwfifo_set_watermark = adxl345_set_watermark,
> > };
> >
> > /**
> > @@ -222,6 +499,7 @@ int adxl345_core_probe(struct device *dev, struct regmap *regmap,
> > unsigned int data_format_mask = (ADXL345_DATA_FORMAT_RANGE |
> > ADXL345_DATA_FORMAT_FULL_RES |
> > ADXL345_DATA_FORMAT_SELF_TEST);
> > + u8 fifo_ctl;
> > int ret;
> >
> > indio_dev = devm_iio_device_alloc(dev, sizeof(*st));
> > @@ -293,6 +571,28 @@ int adxl345_core_probe(struct device *dev, struct regmap *regmap,
> > if (ret < 0)
> > return dev_err_probe(dev, ret, "Failed to add action or reset\n");
> >
> > + if (st->irq > 0) {
> > + dev_dbg(dev, "initialize for FIFO_STREAM mode\n");
> > +
> > + ret = devm_iio_kfifo_buffer_setup(dev, indio_dev, &adxl345_buffer_ops);
> > + if (ret)
> > + return ret;
> > +
> > + ret = devm_request_threaded_irq(dev, st->irq, NULL, &adxl345_event_handler,
> > + IRQF_SHARED | IRQF_ONESHOT,
> > + indio_dev->name, indio_dev);
> > + if (ret)
> > + return dev_err_probe(dev, ret, "Failed to setup triggered buffer\n");
> > +
> > + } else {
> > + dev_dbg(dev, "initialize for FIFO_BYPASS mode (fallback)\n");
> > +
> Given you haven't removed this code from elsewhere, was the driver relying
> on the defaults after reset before this patch?
>
> I don't mind having this branch as a form of documentation even if that's
> true but maybe add a note to the patch description.
>

I'm not sure if I get you correctly. The driver before only
implemented "BYPASS" mode. This was the case w/o a defined
interrupt-name. My intention now is to keep this behavior as fallback.
If no IRQ is around, i.e. interrupt + interrupt-name, the sensor
driver will operate the sensor in BYPASS mode.

I was interpreting this also as the "default behavior", you mentioned
in the dt-binding patch? Is this correct?

What do you mean when the driver is relying on the defaults after reset?

> > + fifo_ctl = ADXL345_FIFO_CTL_MODE(ADXL345_FIFO_BYPASS);
> > +
> > + ret = regmap_write(st->regmap, ADXL345_REG_FIFO_CTL, fifo_ctl);
> > + if (ret < 0)
> > + return ret;
> > + }
> > return devm_iio_device_register(dev, indio_dev);
> > }
> > EXPORT_SYMBOL_NS_GPL(adxl345_core_probe, IIO_ADXL345);
>