linux-kernel - Re: [PATCH RFC v4 15/15] iio: adc: ad4695: Add support for SPI offload

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Message-ID: <7700b27a-9ffc-474e-8390-a69428fe7607@baylibre.com>
Date: Sat, 26 Oct 2024 19:05:44 -0500
From: David Lechner <dlechner@...libre.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Mark Brown <broonie@...nel.org>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Nuno Sá <nuno.sa@...log.com>,
 Uwe Kleine-König <ukleinek@...nel.org>,
 Michael Hennerich <Michael.Hennerich@...log.com>,
 Lars-Peter Clausen <lars@...afoo.de>, David Jander <david@...tonic.nl>,
 Martin Sperl <kernel@...tin.sperl.org>, linux-spi@...r.kernel.org,
 devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-iio@...r.kernel.org, linux-pwm@...r.kernel.org
Subject: Re: [PATCH RFC v4 15/15] iio: adc: ad4695: Add support for SPI
 offload

On 10/26/24 11:00 AM, Jonathan Cameron wrote:
> On Wed, 23 Oct 2024 15:59:22 -0500
> David Lechner <dlechner@...libre.com> wrote:
> 

...

>>  static int ad4695_write_raw(struct iio_dev *indio_dev,
>>  			    struct iio_chan_spec const *chan,
>>  			    int val, int val2, long mask)
>> @@ -779,6 +992,17 @@ static int ad4695_write_raw(struct iio_dev *indio_dev,
>>  			default:
>>  				return -EINVAL;
>>  			}
>> +		case IIO_CHAN_INFO_SAMP_FREQ: {
>> +			struct pwm_state state;
>> +
>> +			if (val <= 0)
>> +				return -EINVAL;
>> +
>> +			guard(mutex)(&st->cnv_pwm_lock);
>> +			pwm_get_state(st->cnv_pwm, &state);
> 
> What limits this to rates the ADC can cope with?
> 

Nothing at the moment. The "obvious" thing to do would
be to limit this to the max rate from the datasheet.

But that feels a little too strict to me since maybe the
PWM can't get exactly the max rate, but can get the max
rate + 1% or so. It seems like we should allow that too.
It's not like the ADC is going to not work if we go a
few Hz over the datasheet rating.

Maybe limit it to max + 10% or something like that?