linux-kernel - Re: [PATCH v1 2/3] iio: light: ROHM BU27008 color sensor

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Date:   Mon, 1 May 2023 16:36:20 +0100
From:   Jonathan Cameron <jic23@...nel.org>
To:     Matti Vaittinen <mazziesaccount@...il.com>
Cc:     Matti Vaittinen <matti.vaittinen@...rohmeurope.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Paul Gazzillo <paul@...zz.com>,
        Shreeya Patel <shreeya.patel@...labora.com>,
        Dmitry Osipenko <dmitry.osipenko@...labora.com>,
        Zhigang Shi <Zhigang.Shi@...eon.com>,
        linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH v1 2/3] iio: light: ROHM BU27008 color sensor

On Mon, 24 Apr 2023 13:14:56 +0300
Matti Vaittinen <mazziesaccount@...il.com> wrote:

> On 4/23/23 15:57, Jonathan Cameron wrote:
> > On Fri, 21 Apr 2023 12:39:36 +0300
> > Matti Vaittinen <mazziesaccount@...il.com> wrote:
> >   
> >> The ROHM BU27008 is a sensor with 5 photodiodes (red, green, blue, clear
> >> and IR) with four configurable channels. Red and green being always
> >> available and two out of the rest three (blue, clear, IR) can be
> >> selected to be simultaneously measured. Typical application is adjusting
> >> LCD backlight of TVs, mobile phones and tablet PCs.
> >>
> >> Add initial support for the ROHM BU27008 color sensor.
> >>   - raw_read() of RGB and clear channels
> >>   - triggered buffer w/ DRDY interrtupt
> >>
> >> Signed-off-by: Matti Vaittinen <mazziesaccount@...il.com>
> >> +
> >> +static int bu27008_meas_set(struct bu27008_data *data, bool enable)
> >> +{
> >> +	if (enable)
> >> +		return regmap_set_bits(data->regmap, BU27008_REG_MODE_CONTROL3,
> >> +				       BU27008_MASK_MEAS_EN);
> >> +
> >> +	return regmap_clear_bits(data->regmap, BU27008_REG_MODE_CONTROL3,
> >> +				 BU27008_MASK_MEAS_EN);  
> > 
> > Might be cleaner with regmap_update_bits()
> >   
> >> +}  
> 
> Hm. I need to disagree on this although I think it depends on what one 
> is used to :)
> 
> For me adding a variable for value to be used is slightly more complex 
> than just using clear or set function depending on the enable/disable. I 
> remember thinking the same as you and preferring the update_bits also on 
> enable/disable cases - until I wrote my first power-supply driver and 
> Sebasian Reichel told me to not do:
> 
> int val;
> 
> if (foo)
> 	val = mask;
> else
> 	val = 0;
> 
> return regmap_update_bits(regmap, reg, mask, val);
> 
> but use set/clear bits. This allows killing the 'int val;'. I remember I 
> had to sleep over night on it but I later started seeing the set/clear 
> bits as a simpler thing.
> 
> Sure we could also do
> 
> if (foo)
> 	return regmap_update_bits(map, reg, mask, mask);
> else
> 	return regmap_update_bits(map, reg, mask, 0);
> 
> - but here we just replace:
> 
> regmap_set_bits(map, reg, mask) with
> regmap_update_bits(map, reg, mask, mask)
> 
> and
> 
> regmap_clear_bits(map, reg, mask)
> regmap_update_bits(map, reg, mask, 0)
> 
> with longer but functionally same variants - which kind of says "I think 
> the "regmap_set_bits() and regmap_clear_bits()" are useless ;)
> 
> After saying this - I can use the regmap_update_bits() if you insist, 
> but in my (not always so) humble opinion this does not improve the function.

Makes sense.  Leave it as it stands.


> 
> 
> >> +
> >> +static int bu27008_set_drdy_irq(struct bu27008_data *data, bool state)
> >> +{
> >> +	if (state)
> >> +		return regmap_set_bits(data->regmap, BU27008_REG_MODE_CONTROL3,
> >> +					BU27008_MASK_INT_EN);
> >> +	return regmap_clear_bits(data->regmap, BU27008_REG_MODE_CONTROL3,
> >> +				 BU27008_MASK_INT_EN);  
> > regmap_update_bits() maybe with the mask and value supplied.  
> 
> Same weak objection here as was with the bu27008_meas_set(). Eg, can 
> change if required but please reconsider :)
Sure. Was a 'maybe' :)

> 
> >> +}
> >> +  


> >> +
> >> +static irqreturn_t bu27008_irq_thread_handler(int irq, void *private)
> >> +{
> >> +	struct iio_dev *idev = private;
> >> +	struct bu27008_data *data = iio_priv(idev);
> >> +	irqreturn_t ret = IRQ_NONE;
> >> +
> >> +	mutex_lock(&data->mutex);
> >> +	if (data->trigger_enabled) {
> >> +		iio_trigger_poll_nested(data->trig);  
> > 
> > Add a comment here on why it makes sense to hold the mutex whilst
> > calling this.  
> 
> After revising this - I don't think it makes. Nor do I think we need the 
> trigger_enable flag so we don't propably need the mutex in buffer enable 
> either as all raw-write configs are claiming the direct mode.

Clearing this out meant I noticed the oddity of doing this in the thread
at all.  So all good in the end ;)

Jonathan