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

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Message-ID: <Y2XtGTAjEB24tqrF@google.com>
Date:   Fri, 4 Nov 2022 21:56:57 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.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 5/6] gpiolib: consolidate GPIO lookups

On Fri, Nov 04, 2022 at 11:06:58PM +0200, Andy Shevchenko wrote:
> On Fri, Nov 04, 2022 at 11:52:26AM -0700, Dmitry Torokhov wrote:
> > On Fri, Nov 04, 2022 at 07:17:27PM +0200, Andy Shevchenko wrote:
> > > On Thu, Nov 03, 2022 at 11:10:15PM -0700, 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)
> > > >  {
> > > 
> > > > +	struct gpio_desc *desc = ERR_PTR(-ENOENT);
> > > 
> > > No need, just return directly.
> > > 
> > > > +	dev_dbg(consumer, "GPIO lookup for consumer %s in node '%s'\n",
> > > > +		con_id, fwnode_get_name(fwnode));
> > > 
> > > %pfwP ?
> > 
> > OK. Although, I think I like %pfw (without 'P') better as it gives
> > results like:
> > 
> > 	/soc/i2c@...07000/edp-bridge@8
> > 
> > or
> > 
> > 	\_SB.PCI0.I2C1.D010
> > 
> > which should help identifying the exact node.
> 
> I agree.
> 
> > > > +	/* Using device tree? */
> > > >  	if (is_of_node(fwnode)) {
> > > > +		dev_dbg(consumer, "using device tree for GPIO lookup\n");
> > > > +		desc = of_find_gpio(to_of_node(fwnode),
> > > > +				    con_id, idx, lookupflags);
> > > >  	} else if (is_acpi_node(fwnode)) {
> > > 
> > > With direct return, no need for 'else' here.
> > 
> > When we have several branches of equal weight I prefer not to have
> > early/inline returns, but I can add:
> > 
> > 	} else {
> > 		desc = ERR_PTR(-ENOENT);
> > 	}
> > 
> > at the end, what do you think?
> 
> No strong opinion here.
> 
> > > > +		dev_dbg(consumer, "using ACPI for GPIO lookup\n");
> > > > +		desc = acpi_find_gpio(fwnode, con_id, idx, flags, lookupflags);
> > > >  	}
> > > >  
> > > > +	return desc;
> > > > +}
> 
> ...
> 
> > > > +	struct gpio_desc *desc = ERR_PTR(-ENOENT);
> > > 
> > > We can get rid of the assignment, see below.
> 
> Still below another thought which affects this.
> 
> > > > +	if (fwnode)
> > > 
> > > Do we need this check?
> > 
> > Yes, I would prefer to have it as it clearly informs the reader that we
> > are only doing lookup by node if we actually have a node.
> > 
> > gpiod_find_and_request() expects that it gets a valid node and in the
> > followup change it will be dereferencing fwnode without checking for
> > NULL-ness.
> 
> But most of the code will check for the NULL anyway. The exceptions are
> dev_dbg() and accessing to the secondary fwnode.

I think it is just a matter of what I want to express through source. I
want to show that the device might not have fwnode, and that we only
descend into gpiod_find_by_fwnode() in cases where we actually have
fwnode.

> 
> > > Debug message above (when %pfw is used) would be even useful when
> > > fwnode == NULL.
> 
> > > > +		desc = gpiod_find_by_fwnode(fwnode, consumer, con_id, idx,
> > > > +					    &flags, &lookupflags);
> 
> Looking into drivers/base/property.c makes me realize that you might need to
> test for error pointer as well.
> 
> Perhaps something like
> 
> 	if (IS_ERR_OR_NULL(fwnode))
> 		return ERR_PTR(-ENOENT);
> 
> in the gpiod_find_by_fwnode() needs to be added. Can you check this?

No, only fwnode->secondary pointer can be PTR_ERR()-encoded.

>From comment to set_primary_fwnode() in drivers/base/core.c

 * Valid fwnode cases are:
 *  - primary --> secondary --> -ENODEV
 *  - primary --> NULL
 *  - secondary --> -ENODEV
 *  - NULL

I do not believe we should be concerned about someone passing secondary
pointers from fwnodes directly into gpiolib.

Thanks.

-- 
Dmitry