linux-kernel - Re: [PATCH v2 5/6] gpiolib: consolidate GPIO lookups

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Date:   Thu, 10 Nov 2022 15:42:40 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Bartosz Golaszewski <brgl@...ev.pl>,
        linux-acpi@...r.kernel.org, linux-gpio@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] gpiolib: consolidate GPIO lookups

On Wed, Nov 09, 2022 at 11:00:29AM -0800, Dmitry Torokhov wrote:
> On Wed, Nov 09, 2022 at 01:25:06PM +0200, Andy Shevchenko wrote:
> > On Tue, Nov 08, 2022 at 04:26:50PM -0800, Dmitry Torokhov wrote:

...

> > > +static struct gpio_desc *gpiod_find_by_fwnode(struct fwnode_handle *fwnode,
> > > +					      struct device *consumer,
> > > +					      const char *con_id,
> > > +					      unsigned int idx,
> > > +					      enum gpiod_flags *flags,
> > > +					      unsigned long *lookupflags)
> > >  {
> > > -	unsigned long lflags = GPIO_LOOKUP_FLAGS_DEFAULT;
> > 
> > > -	struct gpio_desc *desc = ERR_PTR(-ENODEV);
> > 
> > Not sure why this is needed. Now I see that else branch has been changed,
> > but looking closer to it, we can drop it completely, while leaving this
> > line untouched, correct?
> 
> Yes. I believe removing an initializer and doing a series of if/else
> if/else was discussed and [soft] agreed-on in the previous review cycle,
> but I can change it back.
> 
> I think we still need to have it return -ENOENT and not -ENODEV/-EINVAL
> so that we can fall back to GPIO lookup tables when dealing with an
> unsupported node type.

Right, okay, let's go with whatever variant you find better.

...

> > > +	if (!IS_ERR_OR_NULL(fwnode))
> > 
> > I think this is superfluous check.
> > 
> > Now in the form of this series, you have only a single dev_dbg() that tries to
> > dereference it. Do we really need to have it there, since every branch has its
> > own dev_dbg() anyway?
> 
> As I mentioned, I like to keep this check to show the reader that we
> should only descend into gpiod_find_by_fwnode() if we have a valid
> fwnode. It is less about code generation and more about the intent.

Yes, but if fwnode is not found, we have a next check for that. I really don't
think we lose anything by dropping the check and gaining the code generation as
a side effect.

-- 
With Best Regards,
Andy Shevchenko