From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH v3 02/15] Driver core: Unified device properties interface for platform firmware Date: Wed, 01 Oct 2014 09:47:40 +0200 Message-ID: <7365448.TlsV4zB2It@wuerfel> References: <1410868367-11056-1-git-send-email-mika.westerberg@linux.intel.com> <1852462.V1jlbi8OPt@vostro.rjw.lan> <7184313.9OdTqVa2eQ@vostro.rjw.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: In-Reply-To: <7184313.9OdTqVa2eQ@vostro.rjw.lan> Sender: linux-kernel-owner@vger.kernel.org To: "Rafael J. Wysocki" Cc: linux-kernel@vger.kernel.org, Greg Kroah-Hartman , Mika Westerberg , linux-acpi@vger.kernel.org, devicetree@vger.kernel.org, Linus Walleij , Alexandre Courbot , Dmitry Torokhov , Bryan Wu , Lee Jones , Grant Likely , Aaron Lu , Darren Hart List-Id: linux-acpi@vger.kernel.org On Wednesday 01 October 2014 04:10:03 Rafael J. Wysocki wrote: > From: "Rafael J. Wysocki" > > Add a uniform interface by which device drivers can request device > properties from the platform firmware by providing a property name > and the corresponding data type. The purpose of it is to help to > write portable code that won't depend on any particular platform > firmware interface. > > Three general helper functions, device_get_property(), > device_read_property() and device_read_property_array() are provided. > The first one allows the raw value of a given device property to be > accessed. The remaining two allow the value of a numeric or string > property and multiple numeric or string values of one array > property to be acquired, respectively. Static inline wrappers are also > provided for the various property data types that can be passed to > device_read_property() or device_read_property_array() for extra type > checking. These look great! > In addition to that, new generic routines are provided for retrieving > properties from device description objects in the platform firmware > in case a device driver needs/wants to access properties of a child > object of a given device object. There are cases in which there is > no struct device representation of such child objects and this > additional API is useful then. Again, three functions are provided, > device_get_child_property(), device_read_child_property(), > device_read_child_property_array(), in analogy with device_get_property(), > device_read_property() and device_read_property_array() described above, > respectively, along with static inline wrappers for all of the propery > data types that can be used. For all of them, the first argument is > a struct device pointer to the parent device object and the second > argument is a (void *) pointer to the child description provided by > the platform firmware (either ACPI or FDT). I still have my reservations against the child accessors, and would like to hear what other people think. Passing a void pointer rather than struct fw_dev_node has both advantages and disadvantages, and I won't complain about either one if enough other people on the DT side would like to see the addition of the child functions. > Finally, device_for_each_child_node() is added for iterating over > the children of the device description object associated with a > given device. > > The interface covers both ACPI and Device Trees. > > This change set includes material from Mika Westerberg and Aaron Lu. > Regarding device_for_each_child_node(), the syntax is inconsistent with what we normally use, which can probably be changed. All of the DT for_each_* helpers are macros that are used like struct device *dev = ...; void *child; /* iterator */ device_for_each_child_node(dev, child) { u32 something; device_child_property_read_u32(dev, child, "propname", &something); do_something(dev, something); } If we get a consensus on having the child interfaces, I'd rather see them done this way than with a callback pointer, for consistency reasons. Arnd