linux-kernel - Re: [PATCH v2 3/4] gpio: adp5585: Add Analog Devices ADP5585 support

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Date: Wed, 29 May 2024 09:16:43 +0300
From: Andy Shevchenko <andy.shevchenko@...il.com>
To: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Cc: linux-kernel@...r.kernel.org, devicetree@...r.kernel.org, 
	linux-gpio@...r.kernel.org, linux-pwm@...r.kernel.org, 
	Bartosz Golaszewski <brgl@...ev.pl>, Conor Dooley <conor+dt@...nel.org>, 
	Krzysztof Kozlowski <krzk+dt@...nel.org>, Lee Jones <lee@...nel.org>, 
	Linus Walleij <linus.walleij@...aro.org>, Rob Herring <robh@...nel.org>, 
	Uwe Kleine-König <ukleinek@...nel.org>, 
	Haibo Chen <haibo.chen@....com>
Subject: Re: [PATCH v2 3/4] gpio: adp5585: Add Analog Devices ADP5585 support

On Tue, May 28, 2024 at 11:20 PM Laurent Pinchart
<laurent.pinchart@...asonboard.com> wrote:
> On Tue, May 28, 2024 at 10:36:06PM +0300, Andy Shevchenko wrote:

..

> > > +   bit = off * 2 + (off > 5 ? 4 : 0);
> >
> > Right, but can you use >= 6 here which immediately follows to the next
> > question, i.e. why not use bank in this conditional?
>
> The ADP5585_BANK() macro is meant to be used with ADP5585_BIT(), for a
> set of registers with the same layout. Here the layout is different, the
> registers contain multi-bit fields. I can't use ADP5585_BIT(), so I'd
> rather not use ADP5585_BANK() either. I have decided to use > 5 instead
> of >= 6 to match the R5 field name in the comment above:
>
>         /*
>          * The bias configuration fields are 2 bits wide and laid down in
>          * consecutive registers ADP5585_RPULL_CONFIG_*, with a hole of 4 bits
>          * after R5.
>          */

First of all, the 5 sounds misleading as one needs to think about "how
many are exactly per the register" and the answer AFAIU is 6. >= 6
shows this. Second, I haven't mentioned _BANK(), what I meant is
something to

  unsigned int bank = ... >= 6 ? : ;

..

> > > +   struct adp5585_dev *adp5585 = dev_get_drvdata(pdev->dev.parent);
> >
> > (see below)
> >
> > > +   struct adp5585_gpio_dev *adp5585_gpio;
> > > +   struct device *dev = &pdev->dev;
> >
> >       struct adp5585_dev *adp5585 = dev_get_drvdata(dev->parent);
>
> I prefer keeping the current ordering, with long lines first, I think
> that's more readable.

Does the compiler optimise these two?

> > > +   struct gpio_chip *gc;
> > > +   int ret;

..

> > > +   device_set_of_node_from_dev(dev, dev->parent);
> >
> > Why not device_set_node()?
>
> Because device_set_of_node_from_dev() is meant for this exact use case,
> where the same node is used for multiple devices. It also puts any
> previous dev->of_node, ensuring proper refcounting when devices are
> unbound and rebound, without being deleted.

When will the refcount be dropped (in case of removal of this device)?
Or you mean it shouldn't?

-- 
With Best Regards,
Andy Shevchenko