Re: [RFC PATCH 4/5] iio: accel: Support Kionix/ROHM KX022A accelerometer

[Matti Vaittinen]

Hi Jonathan,

On 9/22/22 20:03, Jonathan Cameron wrote:
> On Wed, 21 Sep 2022 14:45:35 +0300
> Matti Vaittinen <mazziesaccount@xxxxxxxxx> wrote:
> > +
> > +/*
> > + * The sensor HW can support ODR up to 1600 Hz - which is beyond what most of
> > + * Linux CPUs can handle w/o dropping samples. Also, the low power mode is not
> > + * available for higher sample rates. Thus the driver only supports 200 Hz and
> > + * slower ODRs. Slowest being 0.78 Hz
> > + */
> > +static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("0.78 1.563 3.125 6.25 12.5 25 50 100 200");
> > +static IIO_CONST_ATTR(scale_available,
> > +		      "598.550415 1197.10083 2394.20166 4788.40332");
> > +
> > +static struct attribute *kx022a_attributes[] = {
> > +	&iio_const_attr_sampling_frequency_available.dev_attr.attr,
> > +	&iio_const_attr_scale_available.dev_attr.attr,
>
> Use the read_avail() callback instead of doing these as attributes.
> That makes the values available to consumer drivers...

Am I correct that populating the read_avail() does not add sysfs entries 
for available scale/frequency? Eg, if I wish to expose the supported 
values via sysfs I still need these attributes? Implementing the 
read_avail() as well is not a problem though.

> > +static int kx022a_turn_on_unlock(struct kx022a_data *data)
> > +{
> > +	int ret;
> > +
> This is not used enough that I can see a strong reason for the
> wrapper.  Just put the two calls inline and rename the unlocked case.

In my opinion the kx022a_turn_on_unlock() and  kx022a_turn_off_lock() do 
simplify functions. Especially after I started using the 
iio_device_claim_direct_mode() :) Thus I will leave these for the v2 - 
please ping me again if you still want to see them removed (but I think 
the usage of iio_device_claim_direct_mode() changed this to favour the 
kx022a_turn_on_unlock() and kx022a_turn_off_lock()).

> > +static int kx022a_chip_init(struct kx022a_data *data)
> > +{
> > +	int ret, dummy;
> > +
> > +	/*
> > +	 * Disable IRQs because if the IRQs are left on (for example by
> > +	 * a shutdown which did not deactivate the accelerometer) we do
> > +	 * most probably end up flooding the system with unhandled IRQs
> > +	 * and get the line disabled from SOC side.
> > +	 */
> > +	ret = regmap_write(data->regmap, KX022A_REG_INC4, 0);
>
> Unusual to do this rather than a reset.  Quick look suggests there is
> a suitable software reset (CNTL2)

I switched to the software reset as you suggested. I am not really 
convinced it is a better way. It seems the software reset requires us to 
re-init the regmap cache. Well, I don't think it is a bid geal though - 
just something worth noticing I guess.

> > +
> > +int kx022a_probe_internal(struct device *dev, int irq)
> > +{
> > +	static const char * const regulator_names[] = {"io_vdd", "vdd"};
> > +	struct iio_trigger *indio_trig;
> > +	struct kx022a_data *data;
> > +	struct regmap *regmap;
> > +	unsigned int chip_id;
> > +	struct iio_dev *idev;
> > +	int ret;
> > +
> > +	if (WARN_ON(!dev))
> > +		return -ENODEV;
> > +
> > +	regmap = dev_get_regmap(dev, NULL);
> > +	if (!regmap) {
> > +		dev_err(dev, "no regmap\n");
>
> Use dev_err_probe() for all dev_err() stuff in probe paths.
> It ends up cleaner and we don't care about the tiny overhead
> of checking for deferred.

This one bothers me a bit. It just does not feel correct to pass -EINVAL 
for the dev_err_probe() so the dev_err_probe() can check if -EINVAL != 
-EPROBE_DEFER. I do understand perfectly well the consistent use of 
dev_err_probe() for all cases where we get an error-code from a function 
and return it - but using dev_err_probe() when we hard-code the return 
value in code calling the dev_err_probe() does not feel like "the right 
thing to do" (tm).

Eg, I agree that
return dev_err_probe(dev, ret, "bar");
is nice even if we know the function that gave us the "ret" never 
requests defer (as that can change some day).

However, I don't like issuing:
return dev_err_probe(dev, -EINVAL, "bar");

Well, please let me know if you think the dev_err_probe() should be used 
even in cases where we hard code the return to something...

For v2 I do change the other prints (like the one about failed regmap 
read below).

> > +
> > +		return -EINVAL;
> > +	}
> > +
> > +	idev = devm_iio_device_alloc(dev, sizeof(*data));
> > +	if (!idev)
> > +		return -ENOMEM;
> > +
> > +	data = iio_priv(idev);
> > +
> > +	/*
> > +	 * VDD is the analog and digital domain voltage supply
> > +	 * IO_VDD is the digital I/O voltage supply
> > +	 */
> > +	ret = devm_regulator_bulk_get_enable(dev, ARRAY_SIZE(regulator_names),
> > +					     regulator_names);
> > +	if (ret && ret != -ENODEV)
> > +		return dev_err_probe(dev, ret, "failed to enable regulator\n");
> > +
> > +	ret = regmap_read(regmap, KX022A_REG_WHO, &chip_id);
> > +	if (ret) {
> > +		dev_err(dev, "Failed to access sensor\n");
Yours,
	-- Matti Vaittinen

--
--
Matti Vaittinen
Linux kernel developer at ROHM Semiconductors
Oulu Finland

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