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

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Date:   Sun, 21 Oct 2018 15:14:27 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Song Qiang <songqiang1304521@...il.com>
Cc:     knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
        robh+dt@...nel.org, mark.rutland@....com, preid@...ctromag.com.au,
        himanshujha199640@...il.com, linux-iio@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 3/3] iio: magnetometer: Add driver support for PNI
 RM3100

On Thu, 18 Oct 2018 16:24:15 +0800
Song Qiang <songqiang1304521@...il.com> wrote:

> On 2018/10/13 下午6:19, Jonathan Cameron wrote:
> > On Fri, 12 Oct 2018 15:35:36 +0800
> > Song Qiang<songqiang1304521@...il.com>  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@...il.com>  
> > 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.

We should 'know' which of those it will be though as I assume it is dependent
on the device configuration which we control.

So waiting for say, double, the expected time should be sufficient to detect
that things have gone horribly wrong.

> 
> 
> >> ---
> >>   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?

Ah. I see, I'd missed that the default was picking up that case as well as the
single axes.   It would be interesting to sanity check if it is quicker on
a 'typical' platform to do the all axis read for the BIT(0) | BIT(2) case
and drop the middle value (which would be done using available scan_masks)
or to just do two independent reads.

(I would guess it is worth reading the 'dead' axis).

> 
> 
> All other problems will be fixed in the next patch.
> 
> yours,
> 
> Song Qiang
> 
> 
> ...
Thanks,

Jonathan