Re: [RFC PATCH v4 1/1] iio/scmi: Adding support for IIO SCMI Based Sensors

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Sun, 31 Jan 2021 20:42:20 +0000
Cristian Marussi <cristian.marussi@arm.com> wrote:

> Hi
> 
> a clarification down below regarding something I pointed out in the
> other thread (just to be sure I have not pointed out something
> plain wrong :D)
> 
> Thanks
> 
> Cristian
> 
> On Sun, Jan 31, 2021 at 01:11:41PM +0000, Jonathan Cameron wrote:
> > On Fri, 29 Jan 2021 22:18:18 +0000
> > Jyoti Bhayana <jbhayana@google.com> wrote:
> >   
> > > This change provides ARM SCMI Protocol based IIO device.
> > > This driver provides support for Accelerometer and Gyroscope using
> > > SCMI Sensor Protocol extensions added in the SCMIv3.0 ARM specification
> > > 
> > > Signed-off-by: Jyoti Bhayana <jbhayana@google.com>  
> > 
> > A few minor things noticed on a fresh read through, but mostly I think
> > we are down to figuring out how to deal with the range (as discussed
> > in the thread continuing on v3).
> > 
> > On another note, probably time to drop the RFC or give a bit more detail
> > on why you think this isn't ready to be applied.
> > 
> > Thanks,
> > 
> > Jonathan
> >   
> [snip]
> 
> > > +
> > > +static int scmi_iio_dev_probe(struct scmi_device *sdev)
> > > +{
> > > +	const struct scmi_sensor_info *sensor_info;
> > > +	struct scmi_handle *handle = sdev->handle;
> > > +	struct device *dev = &sdev->dev;
> > > +	struct iio_dev *scmi_iio_dev;
> > > +	u16 nr_sensors;
> > > +	int err, i;
> > > +
> > > +	if (!handle || !handle->sensor_ops) {
> > > +		dev_err(dev, "SCMI device has no sensor interface\n");  
> > I'm going to guess we can't actually get here because the registration
> > would't have happened if either of those are true?
> > If so perhaps drop the error message.
> >   
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	nr_sensors = handle->sensor_ops->count_get(handle);
> > > +	if (!nr_sensors) {
> > > +		dev_dbg(dev, "0 sensors found via SCMI bus\n");  
> > -ENODEV maybe?  
> > > +		return -EINVAL;
> > > +	}
> > > +
> > > +	dev_dbg(dev, "%d sensors found via SCMI bus\n", nr_sensors);  
> > 
> > Clear out any debug prints out that don't provide info that can't be obtained
> > farily easily from elsewhere.  In this case they will either be registered
> > or not and we'll get error messages.
> > These sort of prints bitrot over time so we want to limit them to the truely
> > useful.
> >   
> > > +
> > > +	for (i = 0; i < nr_sensors; i++) {
> > > +		sensor_info = handle->sensor_ops->info_get(handle, i);
> > > +		if (!sensor_info) {
> > > +			dev_err(dev, "SCMI sensor %d has missing info\n", i);
> > > +			return -EINVAL;
> > > +		}
> > > +
> > > +		/* Skipping scalar sensor,as this driver only supports accel and gyro */
> > > +		if (sensor_info->num_axis == 0)
> > > +			continue;  
> > 
> > So there is a situation where this driver never creates anything?  In that path I'd
> > like to see an -ENODEV error return.
> >   
> You mean -ENODEV only if this driver does not find at least one
> good/supported GYRO/ACCEL sensor right ?

Exactly.

> 
> I would expect a system to possibly expose a bunch of other SCMI sensors
> maybe unsupported by this IIO driver but currently handled by other
> drivers, as an example on JUNO a number of temps/volts/currents sensors
> are exposed and handled by the SCMI hwmon driver.
> 
> 
> > > +
> > > +		err = scmi_alloc_iiodev(dev, handle, sensor_info,
> > > +					&scmi_iio_dev);
> > > +		if (err < 0) {
> > > +			dev_err(dev,
> > > +				"failed to allocate IIO device for sensor %s: %d\n",
> > > +				sensor_info->name, err);
> > > +			return err;
> > > +		}
> > > +
> > > +		err = scmi_iio_buffers_setup(scmi_iio_dev);
> > > +		if (err < 0) {
> > > +			dev_err(dev,
> > > +				"IIO buffer setup error at sensor %s: %d\n",
> > > +				sensor_info->name, err);
> > > +			return err;
> > > +		}
> > > +
> > > +		err = devm_iio_device_register(dev, scmi_iio_dev);
> > > +		if (err) {
> > > +			dev_err(dev,
> > > +				"IIO device registration failed at sensor %s: %d\n",
> > > +				sensor_info->name, err);
> > > +			return err;
> > > +		}
> > > +	}
> > > +	return err;
> > > +}
> > > +
> > > +static const struct scmi_device_id scmi_id_table[] = {
> > > +	{ SCMI_PROTOCOL_SENSOR, "iiodev" },  
> > 
> > I'm curious on this.  What actually causes a match on that
> > iiodev?  From digging around the scmi core am I right in thinking
> > that this iiodev id needs to be explicitly listed?
> > 
> > It would be good to include any changes needed there in this
> > series.
> >   
> > > +	{},
> > > +};
> > > +
> > > +MODULE_DEVICE_TABLE(scmi, scmi_id_table);
> > > +
> > > +static struct scmi_driver scmi_iiodev_driver = {
> > > +	.name = "scmi-sensor-iiodev",
> > > +	.probe = scmi_iio_dev_probe,
> > > +	.id_table = scmi_id_table,
> > > +};
> > > +
> > > +module_scmi_driver(scmi_iiodev_driver);
> > > +
> > > +MODULE_AUTHOR("Jyoti Bhayana <jbhayana@google.com>");
> > > +MODULE_DESCRIPTION("SCMI IIO Driver");
> > > +MODULE_LICENSE("GPL v2");  
> >