linux-kernel - Re: [PATCH v4 08/10] iio: adc: Support ROHM BD79124 ADC

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Message-ID: <ccac509c-d063-42f4-a092-bee4014ec9da@gmail.com>
Date: Sun, 2 Mar 2025 15:15:45 +0200
From: Matti Vaittinen <mazziesaccount@...il.com>
To: Jonathan Cameron <jic23@...nel.org>
Cc: Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
 Lars-Peter Clausen <lars@...afoo.de>, Rob Herring <robh@...nel.org>,
 Krzysztof Kozlowski <krzk+dt@...nel.org>, Conor Dooley
 <conor+dt@...nel.org>, Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
 Daniel Scally <djrscally@...il.com>,
 Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
 Sakari Ailus <sakari.ailus@...ux.intel.com>,
 Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
 "Rafael J. Wysocki" <rafael@...nel.org>, Danilo Krummrich <dakr@...nel.org>,
 Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>,
 Chen-Yu Tsai <wens@...e.org>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Samuel Holland <samuel@...lland.org>,
 Hugo Villeneuve <hvilleneuve@...onoff.com>, Nuno Sa <nuno.sa@...log.com>,
 David Lechner <dlechner@...libre.com>,
 Javier Carrasco <javier.carrasco.cruz@...il.com>,
 Guillaume Stols <gstols@...libre.com>,
 Olivier Moysan <olivier.moysan@...s.st.com>,
 Dumitru Ceclan <mitrutzceclan@...il.com>,
 Trevor Gamblin <tgamblin@...libre.com>,
 Matteo Martelli <matteomartelli3@...il.com>,
 Alisa-Dariana Roman <alisadariana@...il.com>,
 Ramona Alexandra Nechita <ramona.nechita@...log.com>,
 AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>,
 linux-iio@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
 linux-renesas-soc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
 linux-sunxi@...ts.linux.dev, Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH v4 08/10] iio: adc: Support ROHM BD79124 ADC

On 02/03/2025 06:10, Jonathan Cameron wrote:
> On Mon, 24 Feb 2025 20:34:30 +0200
> Matti Vaittinen <mazziesaccount@...il.com> wrote:
> 
>> The ROHM BD79124 is a 12-bit, 8-channel, SAR ADC. The ADC supports
>> an automatic measurement mode, with an alarm interrupt for out-of-window
>> measurements. The window is configurable for each channel.
>>
>> The I2C protocol for manual start of the measurement and data reading is
>> somewhat peculiar. It requires the master to do clock stretching after
>> sending the I2C slave-address until the slave has captured the data.
>> Needless to say this is not well suopported by the I2C controllers.
>>
>> Thus the driver does not support the BD79124's manual measurement mode
>> but implements the measurements using automatic measurement mode relying
>> on the BD79124's ability of storing latest measurements into register.
>>
>> The driver does also support configuring the threshold events for
>> detecting the out-of-window events.
>>
>> The BD79124 keeps asserting IRQ for as long as the measured voltage is
>> out of the configured window. Thus the driver masks the received event
>> for a fixed duration (1 second) when an event is handled. This prevents
>> the user-space from choking on the events
>>
>> The ADC input pins can be also configured as general purpose outputs.
>> Those pins which don't have corresponding ADC channel node in the
>> device-tree will be controllable as GPO.
>>
>> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> Some minor stuff inline.

...

>> +#define BD79124_INTERVAL_075 0
> 
> Can we make these units in these explicit?
> #define BD79124_INTERVAL_MS_0_75
> maybe?  Nice to avoid need for comments on what the units are where
> you use these.
> 

Sure, thanks.

>> +#define BD79124_INTERVAL_150 1
>> +#define BD79124_INTERVAL_300 2
>> +#define BD79124_INTERVAL_600 3

...

> 
>> +static void bd79124_re_enable_hi(struct bd79124_data *data, unsigned int channel)
>> +{
>> +	int ret, evbit = BIT(IIO_EV_DIR_RISING);
>> +
>> +	if (!(data->alarm_suppressed[channel] & evbit))
>> +		return;
>> +
>> +	data->alarm_suppressed[channel] &= (~evbit);
> 
> No brackets around the ~evbit.
> Check for other cases of this.
> Otherwise we'll get some script written 'cleanup'.

Sigh. I had a lengthy discussion about this with Andy explaining why I 
like having the parenthesis to avoid any confusion. Well, I suppose I 
have no options if you're strongly opposing them.

...

>> +static void bd79124_alm_enable_worker(struct work_struct *work)
>> +{
>> +	int i;
>> +	struct bd79124_data *data = container_of(work, struct bd79124_data,
>> +						 alm_enable_work.work);
>> +
>> +	guard(mutex)(&data->mutex);
>> +	/*
>> +	 * We should not re-enable the event if user has disabled it while
>> +	 * rate-limiting was enabled.
>> +	 */
> 
> Is this comment suggesting something that isn't done or referring to specific
> code?  I think it wants to be in the function above where the decision is made.

I have to take another look but it seems it got misplaced during the 
road. Thanks!

Agreeing with all the rest, thanks!

Yours,
	-- Matti