Re: [PATCH v4 3/3] iio: magnetometer: Add driver support for PNI RM3100

[Song Qiang]

On 2018/10/13 äå6:19, Jonathan Cameron wrote:
> On Fri, 12 Oct 2018 15:35:36 +0800
> Song Qiang<songqiang1304521@xxxxxxxxx>  wrote:
>
> > PNI RM3100 is a high resolution, large signal immunity magnetometer,
> > composed of 3 single sensors and a processing chip with a MagI2C
> > interface.
> >
> > Following functions are available:
> >   - Single-shot measurement from
> >     /sys/bus/iio/devices/iio:deviceX/in_magn_{axis}_raw
> >   - Triggerd buffer measurement.
> >   - DRDY pin for data ready trigger.
> >   - Both i2c and spi interface are supported.
> >   - Both interrupt and polling measurement is supported, depends on if
> >     the 'interrupts' in DT is declared.
> >
> > Signed-off-by: Song Qiang<songqiang1304521@xxxxxxxxx>
> A few questions for you (getting very close to being good to go btw!)
>
> Why do we have the 3second additional wait for conversions?  I know we
> rarely wait that long, but still seems excessive.
>
> Few more comments inline.
>
> Thanks,
>
> Jonathan

Hi Jonathan,


The measurement time of this device varies from 1.7ms to 13 seconds, 3 seconds 
is just a number in the middle between them. This may be worth discussing, 
hoping to get a better solution from the community.


> > ---
> >   MAINTAINERS                            |   7 +
> >   drivers/iio/magnetometer/Kconfig       |  29 ++
> >   drivers/iio/magnetometer/Makefile      |   4 +
> >   drivers/iio/magnetometer/rm3100-core.c | 627 +++++++++++++++++++++++++
> >   drivers/iio/magnetometer/rm3100-i2c.c  |  58 +++
> >   drivers/iio/magnetometer/rm3100-spi.c  |  64 +++
> >   drivers/iio/magnetometer/rm3100.h      |  17 +
> >   7 files changed, 806 insertions(+)
> >   create mode 100644 drivers/iio/magnetometer/rm3100-core.c
> >   create mode 100644 drivers/iio/magnetometer/rm3100-i2c.c
> >   create mode 100644 drivers/iio/magnetometer/rm3100-spi.c
> >   create mode 100644 drivers/iio/magnetometer/rm3100.h

...

> > +static irqreturn_t rm3100_trigger_handler(int irq, void *p)
> > +{
> > +	struct iio_poll_func *pf = p;
> > +	struct iio_dev *indio_dev = pf->indio_dev;
> > +	unsigned long scan_mask = *indio_dev->active_scan_mask;
> > +	unsigned int mask_len = indio_dev->masklength;
> > +	struct rm3100_data *data = iio_priv(indio_dev);
> > +	struct regmap *regmap = data->regmap;
> > +	int ret, i, bit;
> > +
> > +	mutex_lock(&data->lock);
> > +	switch (scan_mask) {
> > +	case BIT(0) | BIT(1) | BIT(2):
> > +		ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 9);
> > +		mutex_unlock(&data->lock);
> > +		if (ret < 0)
> > +			goto done;
> > +	break;
> > +	case BIT(0) | BIT(1):
> > +		ret = regmap_bulk_read(regmap, RM3100_REG_MX2, data->buffer, 6);
> > +		mutex_unlock(&data->lock);
> > +		if (ret < 0)
> > +			goto done;
> > +	break;
> > +	case BIT(1) | BIT(2):
> > +		ret = regmap_bulk_read(regmap, RM3100_REG_MY2, data->buffer, 6);
> > +		mutex_unlock(&data->lock);
> > +		if (ret < 0)
> > +			goto done;
> > +	break;
> What about BIT(0) | BIT(2)?
>
> Now you can do it like you have here and on that one corner case let the iio core
> demux code take care of it, but then you will need to provide available_scan_masks
> so the core knows it needs to handle this case.

This confused me a little. The available_scan_masks I was using is {BIT(0) | 
BIT(1) | BIT(2), 0x0}. Apparently in this version of patch I would like it to 
handle every circumstances like BIT(0), BIT(0) | BIT(2), BIT(1) | BIT(2), etc. 
Since Phil mentioned he would like this to reduce bus usage as much as we can 
and I want it, too, I think these three circumstances can be read consecutively 
while others can be read one axis at a time. So I plan to let BIT(0) | BIT(2) 
fall into the 'default' section, which reads axis one by one.

My question is, since this handles every possible combination, do I still need 
to list every available scan masks in available_scan_masks?


All other problems will be fixed in the next patch.

yours,

Song Qiang


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