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Date: Wed, 3 Apr 2024 12:53:02 +0300
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Subject: Re: [PATCH 6/6] iio: adc: ad7173: Add support for AD411x devices
To: David Lechner <dlechner@baylibre.com>, dumitru.ceclan@analog.com
Cc: Lars-Peter Clausen <lars@metafoo.de>,
 Michael Hennerich <Michael.Hennerich@analog.com>,
 Jonathan Cameron <jic23@kernel.org>, Rob Herring <robh@kernel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
 Conor Dooley <conor+dt@kernel.org>, linux-iio@vger.kernel.org,
 devicetree@vger.kernel.org, linux-kernel@vger.kernel.org
References: <20240401-ad4111-v1-0-34618a9cc502@analog.com>
 <20240401-ad4111-v1-6-34618a9cc502@analog.com>
 <CAMknhBFdtv84E_S4wa4UW0pO2yiUEk9=jn=_i4F=b8VHdR6v+w@mail.gmail.com>
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From: "Ceclan, Dumitru" <mitrutzceclan@gmail.com>
In-Reply-To: <CAMknhBFdtv84E_S4wa4UW0pO2yiUEk9=jn=_i4F=b8VHdR6v+w@mail.gmail.com>
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On 01/04/2024 22:45, David Lechner wrote:
> On Mon, Apr 1, 2024 at 10:10 AM Dumitru Ceclan via B4 Relay
> <devnull+dumitru.ceclan.analog.com@kernel.org> wrote:
>>
>> From: Dumitru Ceclan <dumitru.ceclan@analog.com>
>>

..

>>  #define AD7175_2_ID                    0x0cd0
>>  #define AD7172_4_ID                    0x2050
>>  #define AD7173_ID                      0x30d0
>> +#define AD4111_ID                      0x30d0
>> +#define AD4112_ID                      0x30d0
>> +#define AD4114_ID                      0x30d0
> 
> It might make it a bit more obvious that not all chips have a unique
> ID if we rename AD7173_ID to AD7173_AD4111_AD4112_AD4114_ID rather
> than introducing multiple macros with the same value.
> 
> Or leave it as AD7173_ID to keep it short and add a comment where it
> is used with 411x chips in ad7173_device_info[].
> 

Sure

>> +#define AD4116_ID                      0x34d0
>> +#define AD4115_ID                      0x38d0
>>  #define AD7175_8_ID                    0x3cd0
>>  #define AD7177_ID                      0x4fd0
>>  #define AD7173_ID_MASK                 GENMASK(15, 4)

..

>>  struct ad7173_device_info {
>>         const unsigned int *sinc5_data_rates;
>>         unsigned int num_sinc5_data_rates;
>>         unsigned int odr_start_value;
>> +       unsigned int num_inputs_with_divider;
>>         unsigned int num_channels;
>>         unsigned int num_configs;
>>         unsigned int num_inputs;
> 
> Probably a good idea to change num_inputs to num_voltage_inputs so it
> isn't confused with the total number of inputs.
> 
> Similarly num_voltage_inputs_with_divider instead of num_inputs_with_divider.
> 
> Also could use a comment to make it clear if num_voltage_inputs
> includes num_voltage_inputs_with_divider or not. And that it doesn't
> include VINCOM.
> 

Alright for these 3 statements above.

> Probably also need some flag here to differentiate ADCINxx voltage
> inputs on AD4116.
> 

That is the purpose of num_inputs_with_divider. Mangled some changes
when splitting into individual patches. Will include in V2.
"
if (ain[1] == AD411X_VCOM_INPUT &&
		    ain[0] >= st->info->num_inputs_with_divider)
			return dev_err_probe(dev, -EINVAL,
		"VCOM must be paired with inputs having divider.\n");
"

..

>>
>> +static unsigned int ad4111_current_channel_config[] = {
>> +       [AD4111_CURRENT_IN0P_IN0N] = 0x1E8,
>> +       [AD4111_CURRENT_IN1P_IN1N] = 0x1C9,
>> +       [AD4111_CURRENT_IN2P_IN2N] = 0x1AA,
>> +       [AD4111_CURRENT_IN3P_IN3N] = 0x18B,
>> +};
> 
> As mentioned in the DT bindings review, it would make more sense to
> just use the datasheet numbers for the current input channels in the
> diff-channels DT property, then we don't need this lookup table.
>
Yet, the datasheet does not specify the numbers, just a single bitfield
for each pair. It is too much of a churn to need to decode that bitfield
into individual values when the user just wants to select a single pair.

..

>> +               case IIO_CURRENT:
>> +                       *val = ad7173_get_ref_voltage_milli(st, ch->cfg.ref_sel);
>> +                       *val /= AD4111_SHUNT_RESISTOR_OHM;
>> +                       *val2 = chan->scan_type.realbits - !!(ch->cfg.bipolar);
> 
> Static analysis tools like to complain about using bool as int.
> Probably more clear to write it as (ch->cfg.bipolar ? 1 : 0) anyway.
> 
Maybe it does not apply here, but i followed this advice:

Andy Shevchenko V1 of AD7173 (named initially ad717x)
"
> +	return (bool)(value & mask);

This is weird. You have int which you get from bool, wouldn't be better
to use
!!(...) as other GPIO drivers do?

"


>> +               case IIO_CURRENT:
>>                         *val = -BIT(chan->scan_type.realbits - 1);
> 
> Expecting a special case here, at least when ADCIN15 is configured for
> pseudo-differential inputs.
> 

And what configuration would that be?
The only configurable part is the BI_UNIPOLARx bit in the channel
register, which is addressed here.

There seems to be a confusion similar to what we had with single-ended
channels. The ADC is differential. Pseudo-differential in this datasheet
just means that you wired a fixed voltage(higher than 0) to the negative
analog input.

 Which you can also do on the other inputs with a divider.

..

>> -               chan_st_priv->ain = AD7173_CH_ADDRESS(ain[0], ain[1]);
>> +               if (reg >= AD4111_CURRENT_CHAN_CUTOFF) {
>> +                       chan->type = IIO_CURRENT;
>> +                       chan->channel = ain[0];
>> +                       chan_st_priv->ain = ad4111_current_channel_config[ain[0]];
>> +               } else {
>> +                       chan->channel = ain[0];
>> +                       chan->channel2 = ain[1];
>> +                       chan->differential = true;
> 
> Expecting chan->differential = false when ADCIN15 is configured for
> pseudo-differential inputs.
> 
> Also, perhaps missed in previous reviews, I would expect
> chan->differential = false when channels are used as single-ended.
>
Why?
Also, how would one detect if you are using single-ended channels?

The ADC is still differential. Single ended is represented as connecting
AVSS(or another fixed voltage) and only letting the AIN+ input to fluctuate.

In the IIO framework the only difference this makes is in the naming of
the channel:
 voltage0-voltage1 vs just voltage0

All channels are differential. Pseudo differential: still differential.