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Date:	Mon, 20 Oct 2014 16:18:18 +0200
From:	Grant Likely <grant.likely@...aro.org>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Arnd Bergmann <arnd@...db.de>,
	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 Mon, 20 Oct 2014 01:46 +0200
, "Rafael J. Wysocki" <rjw@...ysocki.net>
 wrote:
> On Saturday, October 18, 2014 04:55:20 PM Grant Likely wrote:
> > On Fri, 17 Oct 2014 14:14:53 +0200
> > , "Rafael J. Wysocki" <rjw@...ysocki.net>
> >  wrote:
> > > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > > 
> > > Add new generic routines are provided for retrieving properties from
> > > device description objects in the platform firmware in case there are
> > > no struct device objects for them (either those objects have not been
> > > created yet or they do not exist at all).
> > > 
> > > The following functions are provided:
> > > 
> > > fwnode_property_present()
> > > fwnode_property_read_u8()
> > > fwnode_property_read_u16()
> > > fwnode_property_read_u32()
> > > fwnode_property_read_u64()
> > > fwnode_property_read_string()
> > > fwnode_property_read_u8_array()
> > > fwnode_property_read_u16_array()
> > > fwnode_property_read_u32_array()
> > > fwnode_property_read_u64_array()
> > > fwnode_property_read_string_array()
> > > 
> > > in analogy with the corresponding functions for struct device added
> > > previously.  For all of them, the first argument is a pointer to struct
> > > fwnode_handle (new type) that allows a device description object
> > > (depending on what platform firmware interface is in use) to be
> > > obtained.
> > > 
> > > Add a new macro device_for_each_child_node() for iterating over the
> > > children of the device description object associated with a given
> > > device and a new function device_get_child_node_count() returning the
> > > number of a given device's child nodes.
> > > 
> > > The interface covers both ACPI and Device Trees.
> > 
> > This is all *so much* better. I'm a lot happier.
> > 
> > I was about to make the comment that the implementation for
> > device_property_read_*() should merely be wrappers around
> > fwnode_property_read_*(), but when when I actually looked at it, I saw
> > this:
> > 
> > In patch 2:
> > int device_property_read_u8(struct device *dev, const char *propname, u8 *val)
> > {
> > 	if (IS_ENABLED(CONFIG_OF) && dev->of_node)
> > 		return of_property_read_u8(dev->of_node, propname, val);
> > 
> > 	return acpi_dev_prop_read(ACPI_COMPANION(dev), propname,
> > 				  DEV_PROP_U8, val);
> > }
> > 
> > And in this patch:
> > int fwnode_property_read_u8(struct fwnode_handle *fwnode, const char *propname,
> > 			    u8 *val)
> > {
> > 	if (is_of_node(fwnode))
> > 		return of_property_read_u8(of_node(fwnode), propname, val);
> > 	else if (is_acpi_node(fwnode))
> > 		return acpi_dev_prop_read(acpi_node(fwnode), propname,
> > 					  DEV_PROP_U8, val);
> > 
> > 	return -ENXIO;
> > }
> > 
> > Making the device_property functions wrappers around fwnode_property_*
> > wouldn't actually be great since it would need to decode the fwnode
> > pointer twice.
> 
> Indeed.
> 
> > I do still think the functions above should be macro generated, just in
> > terms of keeping the line count down, and I would suggest merging patches #2
> > and #9.
> 
> Well, the changes in those patches are almost completely independent and patch
> #9 is only actually needed for #11 and #12, so I'm not sure if that would be
> better.  I certainly prefer splitting longer patches into pieces if that makes
> sense and it does make sense to do so in this particular case IMHO.

I'm not going to make a big deal about. Do what you think is best.

> > 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. ;-)
> 
> 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.

I'm fine with that. It's the near-identical blocks of code that I'm
concerned about. It is easy to miss one instance when fixing bugs if
they all have to be open coded. Plus it simply means a lot more lines of
code to wade through and review.

> > Also, can the non-array versions be implemented as a wrapper around the
> > array versions? That also will reduce the sheer number of lines of code
> > a lot.
> > 
> > Maybe this:
> > 
> > #define define_fwnode_accessors(__type, __devprop_type) \
> > int device_property_read_##__type##_array(struct device *dev, \
> > 				const char *propname, __type *val, \
> > 				size_t nval) \
> > { \
> > 	if (IS_ENABLED(CONFIG_OF) && dev->of_node) \
> > 		return of_property_read_##__type##_array(dev->of_node, \
> > 		propname, val, nval); \
> > 	return acpi_dev_prop_read_array(ACPI_COMPANION(dev), propname, \
> > 				  __devprop_type, val, nval); \
> > } \
> > static inline int device_property_read_##__type(struct device *dev, \
> > 				const char *propname, __type *val) \
> > { \
> > 	return device_property_read_##__type##_array(dev, propname, val, 1) \
> > } \
> > int fwnode_property_read_##__type##_array(struct fwnode_handle *fwnode, \
> > 				const char *propname, __type *val, \
> > 				size_t nval) \
> > { \
> > 	if (IS_ENABLED(CONFIG_OF) && is_of_node(fwnode)) \
> > 		return of_property_read_##__type(of_node(fwnode), propname, val, nval); \
> > 	else if (IS_ENABLED(CONFIG_ACPI) && is_acpi_node(fwnode)) \
> > 		return acpi_dev_prop_read(acpi_node(fwnode), propname, \
> > 					  __devprop_type, val, nval); \
> > 	return -ENXIO; \
> > } \
> > static inline int fwnode_property_read_##__type(struct fwnode_handle *fwnode, \
> > 				const char *propname, __type *val) \
> > { \
> > 	return fwnode_property_read_##__type##_array(fwnode, propname, val, 1) \
> > }
> > 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);
> 
> No, that wouldn't work for ACPI (if I understand your idea correctly), because
> acpi_dev_prop_read(adev, propname, DEV_PROP_U8, val) will look for a single-value
> int property, whereas acpi_dev_prop_read_array(adev, propname, DEV_PROP_U8, val, 1)
> will look for a list (package) property and will attempt to retrieve the first
> element of that.

That's a problem. There are certainly cases of DT code that use the
non-array version to read something that could also be read as an array
when the code only want the first value. It is a completely valid thing
to do. The ACPI accessors should be completely okay with either a single
value, or the first item(s) in a package when doing either a single read or
an array read.

so, if it is encoded as a singl values, then return that value, and the
largest size of array it will return is 1 element.

If it is encoded as a package, then a single read should return the
first element, and an array read should return up to the number of
values in the package.

g.

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