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

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Message-ID: <5981363.HuOrK2kMZG@vostro.rjw.lan>
Date:	Tue, 21 Oct 2014 00:22:09 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Arnd Bergmann <arnd@...db.de>
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, October 20, 2014 04:19:57 PM Arnd Bergmann wrote:
> 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.

There is one concatenation like that in the code I have today, but it was
already present in the $subject series, in the of_dev_prop_read_array macro
in patch #2 (and it actually makes sense to me).

Rafael

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