linux-kernel - Re: [PATCH 2/2] iio: frequency: add amlogic clock measure support

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Date: Mon, 24 Jun 2024 18:03:24 -0500
From: David Lechner <dlechner@...libre.com>
To: Jerome Brunet <jbrunet@...libre.com>, Jonathan Cameron
 <jic23@...nel.org>, Lars-Peter Clausen <lars@...afoo.de>,
 Neil Armstrong <neil.armstrong@...aro.org>
Cc: Kevin Hilman <khilman@...libre.com>, linux-kernel@...r.kernel.org,
 linux-amlogic@...ts.infradead.org, linux-iio@...r.kernel.org,
 Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>
Subject: Re: [PATCH 2/2] iio: frequency: add amlogic clock measure support

On 6/24/24 5:51 PM, David Lechner wrote:
> On 6/24/24 12:31 PM, Jerome Brunet wrote:
>> Add support for the HW found in most Amlogic SoC dedicated to measure
>> system clocks.
>>
> 
> 
> 
>> +static int cmsr_read_raw(struct iio_dev *indio_dev,
>> +			 struct iio_chan_spec const *chan,
>> +			 int *val, int *val2, long mask)
>> +{
>> +	struct amlogic_cmsr *cm = iio_priv(indio_dev);
>> +
>> +	guard(mutex)(&cm->lock);
>> +
>> +	switch (mask) {
>> +	case IIO_CHAN_INFO_RAW:
>> +		*val = cmsr_measure_unlocked(cm, chan->channel);
> 
> Is this actually returning an alternating voltage magnitutde?
> Most frequency drivers don't have a raw value, only frequency.
> 
>> +		if (*val < 0)
>> +			return *val;
>> +		return IIO_VAL_INT;
>> +
>> +	case IIO_CHAN_INFO_PROCESSED: /* Result in Hz */
> 
> Shouldn't this be IIO_CHAN_INFO_FREQUENCY?
> 
> Processed is just (raw + offset) * scale which would be a voltage
> in this case since the channel type is IIO_ALTVOLTAGE.
> 
>> +		*val = cmsr_measure_processed_unlocked(cm, chan->channel, val2);
>> +		if (*val < 0)
>> +			return *val;
>> +		return IIO_VAL_INT_64;
>> +
>> +	case IIO_CHAN_INFO_SCALE:
> 
> What is this attribute being used for?
> 
> (clearly not used to convert the raw value to millivolts :-) )
> 
> Maybe IIO_CHAN_INFO_INT_TIME is the right one for this? Although
> so far, that has only been used with light sensors.

Probably not the right idea though since it applies to the frequency
measurement, not the voltage measurement.

> 
>> +		*val2 = cmsr_get_time_unlocked(cm);
>> +		*val = 1000000;
>> +		return IIO_VAL_FRACTIONAL;
>> +
>> +	default:
>> +		return -EINVAL;
>> +	}
>> +}
>> +