linux-kernel - Re: [PATCH v5 09/12] Driver core: Unified interface for firmware node properties

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Date:	Mon, 20 Oct 2014 16:19:57 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Grant Likely <grant.likely@...aro.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mika Westerberg <mika.westerberg@...ux.intel.com>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Aaron Lu <aaron.lu@...el.com>, devicetree@...r.kernel.org,
	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	Bryan Wu <cooloney@...il.com>,
	Darren Hart <dvhart@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>
Subject: Re: [PATCH v5 09/12] Driver core: Unified interface for firmware node properties

On Monday 20 October 2014 01:46:00 Rafael J. Wysocki wrote:
> 
> > Something like:
> > 
> > #define define_fwnode_accessors(__type, __devprop_type) \
> > int device_property_read_##__type(struct device *dev, \
> >                               const char *propname, __type *val) \
> > { \
> >       if (IS_ENABLED(CONFIG_OF) && dev->of_node) \
> >               return of_property_read_##__type(dev->of_node, propname, val); \
> >       return acpi_dev_prop_read(ACPI_COMPANION(dev), propname, \
> >                                 __devprop_type, val); \
> > } \
> > int fwnode_property_read_##__type(struct fwnode_handle *fwnode, \
> >                               const char *propname, __type *val) \
> > { \
> >       if (IS_ENABLED(CONFIG_OF) && is_of_node(fwnode)) \
> >               return of_property_read_##__type(of_node(fwnode), propname, val); \
> >       else if (IS_ENABLED(CONFIG_ACPI) && is_acpi_node(fwnode)) \
> >               return acpi_dev_prop_read(acpi_node(fwnode), propname, \
> >                                         __devprop_type, val); \
> >       return -ENXIO; \
> > }
> > 
> > define_fwnode_accessors(u8, DEV_PROP_U8);
> > define_fwnode_accessors(u16, DEV_PROP_U16);
> > define_fwnode_accessors(u32, DEV_PROP_U32);
> > define_fwnode_accessors(u64, DEV_PROP_U64);
> > 
> > That significantly reduces the code size for these things.
> 
> So I was considering to do that, but eventually decided not to, because (1)
> adding kerneldoc comments to such things looks odd and (2) (which IMO is
> more important) this breaks LXR (for example, the thing at lxr.free-electrons.com
> that some people, including me in particular, occasionally use to check how things
> are defined).  And even if you used the old good grep to look for a definition of
> fwnode_property_read_u8, say, this wouldn't work exactly as expected I'm afraid. 

Agreed, I'd also prefer your proposed code over Grant's macros.

> I would very much like to retain the headers at least for this reason, if that's
> not a big deal.
> 
> What I can do, however, is to use macros for generating the bodies of those
> functions.

Yes, just don't do any concatenation to generate the names of the called
functions, i.e.

	return fwnode_call(of_property_read_u32, acpi_dev_prop_read, DEV_PROP_U32, node, propname, val);

is better than

	return fwnode_call(u32, DEV_PROP_U32, node, propname, val);

because it's easier to understand the call chain.

	Arnd
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