Il giorno dom 27 ott 2019 alle ore 10:23 Jonathan Cameron
<jic23@xxxxxxxxxx> ha scritto:
>
> On Wed, 23 Oct 2019 10:29:07 +0200
> Andrea Merello <andrea.merello@xxxxxxxxx> wrote:
>
> > Il giorno mar 22 ott 2019 alle ore 11:35 Jonathan Cameron
> > <jic23@xxxxxxxxxx> ha scritto:
> > >
> > > On Fri, 18 Oct 2019 15:46:32 +0200
> > > Andrea Merello <andrea.merello@xxxxxxxxx> wrote:
> > >
> > > > Il giorno gio 17 ott 2019 alle ore 14:32 Jonathan Cameron
> > > > <jonathan.cameron@xxxxxxxxxx> ha scritto:
> > > > >
> > > > > On Wed, 16 Oct 2019 15:14:20 +0200
> > > > > Andrea Merello <andrea.merello@xxxxxxxxx> wrote:
> > > > >
> > > > > > Il giorno dom 6 ott 2019 alle ore 09:54 Jonathan Cameron
> > > > > > <jic23@xxxxxxxxxx> ha scritto:
> > > > > > >
> > > > > > > On Mon, 23 Sep 2019 14:17:12 +0200
> > > > > > > Andrea Merello <andrea.merello@xxxxxxxxx> wrote:
> > > > > > >
> > > > > > > > This sensor has an embedded notch filter for reducing interferences caused
> > > > > > > > by the power mains. This filter can be tuned to reject either 50Hz or 60Hz
> > > > > > > > (and harmonics).
> > > > > > > >
> > > > > > > > Currently the said setting is left alone (the sensor defaults to 60Hz).
> > > > > > > > This patch introduces a IIO attribute that allows the user to set the said
> > > > > > > > filter to the desired frequency.
> > > > > > > >
> > > > > > > > NOTE: this has been intentionally not tied to any DT property to allow
> > > > > > > > the configuration of this setting from userspace, e.g. with a GUI or by
> > > > > > > > reading a configuration file, or maybe reading a GPIO tied to a physical
> > > > > > > > switch or accessing some device that can autodetect the line frequency.
> > > > > > > >
> > > > > > > > Signed-off-by: Andrea Merello <andrea.merello@xxxxxxxxx>
> > > > > > > This one is not something that can be expect to be known from the setup
> > > > > > > of the device as it will depend on local mains frequency.
> > > > > > >
> > > > > > > So fine, to have it as a userspace control, but the name is too generic.
> > > > > > > We already have a number of filter attributes and we should try to
> > > > > > > work out how to bring it inline with them.
> > > > > >
> > > > > > Sure
> > > > > >
> > > > > > > in_X_filter_low_pass_3db_frequency
> > > > > > > in_X_filter_high_pass_3db_frequency
> > > > > > >
> > > > > > > So would,
> > > > > > > in_X_filter_notch_center_frequency work?
> > > > > > > ( I suppose we should use the American spelling ;)
> > > > > >
> > > > > > Yes, it seems OK in this case. I will produce a V2 with this modification.
> > > > > >
> > > > > > > This kind of ignores the harmonics aspect but at least documents the
> > > > > > > main frequency being blocked.
> > > > > >
> > > > > > I think this is perfectly fine: the user wants to set the notch filter
> > > > > > center frequency to either 60Hz or 50Hz to match the line frequency,
> > > > > > then she/he expects the filter to simply "work" somehow; IMO the
> > > > > > harmonic thing does not needed to be explicit.
> > > > > >
> > > > > > > There is a slight complexity that we have devices that have dual
> > > > > > > notchfilters (50 and 60Hz) and ones where you can turn it off entirely.
> > > > > > >
> > > > > > > I suppose no value would count as off and we could perhaps use a list
> > > > > > > for both on at the same time (though that's a bit horrible).
> > > > > >
> > > > > > IMHO it seems reasonable. Maybe for all-off and both-on conditions we
> > > > > > could also use magic strings like i.e. "all" and "off".
> > > > >
> > > > > I go with 'maybe' on that one. Need to think about whether that is just
> > > > > a partial solution as we will probably find a device with 3 options that only
> > > > > supports any 2 at one time. That would still need a more complex interface.
> > > > >
> > > > > Will think on this.
> > > >
> > > > I'll keep this patch on hold, waiting for your thoughts. Take the time
> > > > you need :)
> > > >
> > > > BTW IMHO:
> > > >
> > > > If we want to address the most possible generic case, then we may
> > > > standardize a set of possible attributes for filters (like "enable",
> > > > "center_frequency", "width", "Q" , etc). Of course most filters will
> > > > not allow for setting most of those attributes.
> > >
> > > Absolutely. We currently have a few defined for low and high pass
> > > filters, but if there are more complex features to define we should
> > > do so.
> > >
> > > >
> > > > Then i.e. in our case we could have one single filter that allows for
> > > > setting the frequency to either 50hz or 60hz; in other cases we could
> > > > have i.e. two filters (with 50hz and 60hz center freq respectively),
> > > > and they would allow to set only the "enable" attribute; in case you
> > > > can i.e. enable only two of three filters, when you try to enable the
> > > > 3rd it just refuse that. In this scenario probably "center_frequency"
> > > > could be just a regular value (not a list).
> > >
> > > Agreed. The question is whether to index filters. So allow more
> > > than one of a given type on a given channel. So far we have
> > > only had the one and there isn't a nice way to support multiple
> > > as we currently don't have any indexed parameters of a single channel.
> >
> > Yes, being able to indexing filters was the underlying assumption..
> >
> > > I haven't seen parts that actually do have this level of sophisticated
> > > filtering built in, with the exception of mains filters like this one.
> >
> > Yes, I didn't too indeed.
> >
> > > I think we have to allow for the possibility so if you are happy to do
> > > so please propose the ABI additions to support multiple filters of
> > > a type. I would suggest keeping them per type though
> > >
> > > e.g.
> > >
> > > in_X_filter_low_passY_3db_frequency etc
> > > with Y as the optional index.
> >
> > Seems reasonable.
> >
> > Well the idea is the one you've just explained here, that is adding an
> > optional index for filters (per type and per ch); I'm not getting what
> > do you mean about proposing it..
> Like all new ABI, needs a formal documentation patch. Sometimes
> we get more review on those than on discussions deep in a thread like
> this.
OK, this is honestly a bit out of my scope, but - if this is OK for
you - I may try to do that after getting to some end with those
in-flight patches..
> >
> > > For now, lets just implement then using extended attributes rather
> > > than trying to extend the core to generate these automatically.
> > >
> > > If this turns out not to be a corner case we can try to figure
> > > out a sane way of generating the multiple indexed versions.
> >
> > OK. Let's try not to over-complicate things until it's really needed -
> > Also, maybe if we'll hit other weird devices that need something like
> > this, then they could have some exotic features that we haven't in
> > mind yet now; it might turn out that we need something even more
> > different, so maybe it's better to wait for real "users" of the ABI
> > before deciding how to change it..
> >
> > But indeed, getting back to the patch originally discussed in this
> > thread: if you are OK whit this, then I'll go with a
> > "in_temp_filter_notch_center_frequency" attribute.
> >
> > I may use a specific IIO_DEVIC_ATTR or add it to the core (without
> > addressing the index thing), as you prefer.
>
> Which ever makes most sense to you. Either is fine for a new
> attribute, though here don't we need the indexed filters?
This specific device has only the option to choose either 50Hz
filtering or 60Hz filtering; no option to disable filtering or enable
both frequency. So I would say that here we can expose just one filter
for which the center frequency can be set to either 50Hz or 60Hz (like
the original patch did - but with proper name this time). I would say
that we don't need indexed filters here. Or have I missed something ?
(So I would start with a IIO_DEVICE_ATTR for now then).
> >
> > BTW: Looking at other drivers, it seems that for other attributes
> > (e.g. oversampling_ratio, discussed in 2/3) they tend to round
> > required values to the closest allowed value, instead of returning an
> > error. In this specific case, do you want to apply the same logic? For
> > consistency reasons I would do that, but at the practical side,
> > requiring a line filter frequency which is not either 50Hz or 60Hz
> > seems really an error to me..
>
> It can be a bit of a tricky decision but for something like this
> where the precise value works, it should reject incorrect ones.
OK
> Oversampling is an odd one. It should probably always round up
> as it's usually not a problem to average more results, it just
> wastes power. That only applies if the oversampling_ratio
> is independent of other attributes such as sampling frequency.
It actually affects also the sampling rate; the more samples you
average, the slowest output rate you achieve. But actually there is no
attribute for setting the sampling frequency.. it is internally
adjusted by the chip depending by averaging and filter line frequency
(don't know why).
(if we want also this attribute, then I can craft another patch for
adding it; it may be usefult to report the actual sample rate, I'm not
sure if it makes sense to let the user set it, because we can
basically just switch the averaging to one of the few possible values
to get the sample rate to change as a side effect - assuming that one
doesn't want to change the line frequency filter).
BTW What about to round the requested oversampling_ratio to the
closest allowed value (instead of rounding up)?
> Still, we have traditionally been relaxed on this as long
> as writing the the 'correct' value always works as that's what
> userspace ABI should be doing.
>
> Jonathan
>
> >
> > >
> > > >
> > > > >
> > > > >
> > > > > Jonathan
> > > > >
> > > > > >
> > > > > > > > ---
> > > > > > > > drivers/iio/temperature/max31856.c | 49 ++++++++++++++++++++++++++++++
> > > > > > > > 1 file changed, 49 insertions(+)
> > > > > > > >
> > > > > > > > diff --git a/drivers/iio/temperature/max31856.c b/drivers/iio/temperature/max31856.c
> > > > > > > > index 73ed550e3fc9..d12613f7ba3c 100644
> > > > > > > > --- a/drivers/iio/temperature/max31856.c
> > > > > > > > +++ b/drivers/iio/temperature/max31856.c
> > > > > > > > @@ -23,6 +23,7 @@
> > > > > > > > #define MAX31856_CR0_1SHOT BIT(6)
> > > > > > > > #define MAX31856_CR0_OCFAULT BIT(4)
> > > > > > > > #define MAX31856_CR0_OCFAULT_MASK GENMASK(5, 4)
> > > > > > > > +#define MAX31856_CR0_FILTER_50HZ BIT(0)
> > > > > > > > #define MAX31856_TC_TYPE_MASK GENMASK(3, 0)
> > > > > > > > #define MAX31856_FAULT_OVUV BIT(1)
> > > > > > > > #define MAX31856_FAULT_OPEN BIT(0)
> > > > > > > > @@ -63,6 +64,7 @@ static const struct iio_chan_spec max31856_channels[] = {
> > > > > > > > struct max31856_data {
> > > > > > > > struct spi_device *spi;
> > > > > > > > u32 thermocouple_type;
> > > > > > > > + bool filter_50hz;
> > > > > > > > };
> > > > > > > >
> > > > > > > > static int max31856_read(struct max31856_data *data, u8 reg,
> > > > > > > > @@ -123,6 +125,11 @@ static int max31856_init(struct max31856_data *data)
> > > > > > > > reg_cr0_val &= ~MAX31856_CR0_1SHOT;
> > > > > > > > reg_cr0_val |= MAX31856_CR0_AUTOCONVERT;
> > > > > > > >
> > > > > > > > + if (data->filter_50hz)
> > > > > > > > + reg_cr0_val |= MAX31856_CR0_FILTER_50HZ;
> > > > > > > > + else
> > > > > > > > + reg_cr0_val &= ~MAX31856_CR0_FILTER_50HZ;
> > > > > > > > +
> > > > > > > > return max31856_write(data, MAX31856_CR0_REG, reg_cr0_val);
> > > > > > > > }
> > > > > > > >
> > > > > > > > @@ -249,12 +256,53 @@ static ssize_t show_fault_oc(struct device *dev,
> > > > > > > > return show_fault(dev, MAX31856_FAULT_OPEN, buf);
> > > > > > > > }
> > > > > > > >
> > > > > > > > +static ssize_t show_filter(struct device *dev,
> > > > > > > > + struct device_attribute *attr,
> > > > > > > > + char *buf)
> > > > > > > > +{
> > > > > > > > + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > > > > > > + struct max31856_data *data = iio_priv(indio_dev);
> > > > > > > > +
> > > > > > > > + return sprintf(buf, "%d\n", data->filter_50hz ? 50 : 60);
> > > > > > > > +}
> > > > > > > > +
> > > > > > > > +static ssize_t set_filter(struct device *dev,
> > > > > > > > + struct device_attribute *attr,
> > > > > > > > + const char *buf,
> > > > > > > > + size_t len)
> > > > > > > > +{
> > > > > > > > + struct iio_dev *indio_dev = dev_to_iio_dev(dev);
> > > > > > > > + struct max31856_data *data = iio_priv(indio_dev);
> > > > > > > > + unsigned int freq;
> > > > > > > > + int ret;
> > > > > > > > +
> > > > > > > > + ret = kstrtouint(buf, 10, &freq);
> > > > > > > > + if (ret)
> > > > > > > > + return ret;
> > > > > > > > +
> > > > > > > > + switch (freq) {
> > > > > > > > + case 50:
> > > > > > > > + data->filter_50hz = true;
> > > > > > > > + break;
> > > > > > > > + case 60:
> > > > > > > > + data->filter_50hz = false;
> > > > > > > > + break;
> > > > > > > > + default:
> > > > > > > > + return -EINVAL;
> > > > > > > > + }
> > > > > > > > +
> > > > > > > > + max31856_init(data);
> > > > > > > > + return len;
> > > > > > > > +}
> > > > > > > > +
> > > > > > > > static IIO_DEVICE_ATTR(fault_ovuv, 0444, show_fault_ovuv, NULL, 0);
> > > > > > > > static IIO_DEVICE_ATTR(fault_oc, 0444, show_fault_oc, NULL, 0);
> > > > > > > > +static IIO_DEVICE_ATTR(filter, 0644, show_filter, set_filter, 0);
> > > > > > > >
> > > > > > > > static struct attribute *max31856_attributes[] = {
> > > > > > > > &iio_dev_attr_fault_ovuv.dev_attr.attr,
> > > > > > > > &iio_dev_attr_fault_oc.dev_attr.attr,
> > > > > > > > + &iio_dev_attr_filter.dev_attr.attr,
> > > > > > > > NULL,
> > > > > > > > };
> > > > > > > >
> > > > > > > > @@ -280,6 +328,7 @@ static int max31856_probe(struct spi_device *spi)
> > > > > > > >
> > > > > > > > data = iio_priv(indio_dev);
> > > > > > > > data->spi = spi;
> > > > > > > > + data->filter_50hz = false;
> > > > > > > >
> > > > > > > > spi_set_drvdata(spi, indio_dev);
> > > > > > > >
> > > > > > >
> > > > >
> > > > >
> > >
>
