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

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Message-ID: <20241027091508.2572785a@jic23-huawei>
Date: Sun, 27 Oct 2024 09:15:08 +0000
From: Jonathan Cameron <jic23@...nel.org>
To: David Lechner <dlechner@...libre.com>
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 Sat, 26 Oct 2024 19:05:44 -0500
David Lechner <dlechner@...libre.com> wrote:

> 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?

Clamp it at datasheet value.   That's what is presumably verified
not 10% over.  If that needs relaxing in future, the datasheet should
be updated to reflect the higher verified value.

Jonathan