From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753605AbaJAWl2 (ORCPT ); Wed, 1 Oct 2014 18:41:28 -0400 Received: from v094114.home.net.pl ([79.96.170.134]:63742 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1752050AbaJAWl0 (ORCPT ); Wed, 1 Oct 2014 18:41:26 -0400 From: "Rafael J. Wysocki" To: Arnd Bergmann 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 Subject: Re: [PATCH v3 02/15] Driver core: Unified device properties interface for platform firmware Date: Thu, 02 Oct 2014 01:01:18 +0200 Message-ID: <1736273.lW0BdXdkei@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <4390403.PNxQqnBDGX@vostro.rjw.lan> References: <1410868367-11056-1-git-send-email-mika.westerberg@linux.intel.com> <7365448.TlsV4zB2It@wuerfel> <4390403.PNxQqnBDGX@vostro.rjw.lan> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="utf-8" Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thursday, October 02, 2014 12:09:44 AM Rafael J. Wysocki wrote: > On Wednesday, October 01, 2014 09:47:40 AM Arnd Bergmann wrote: > > 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. > > I actually would rather like to know if the people on the DT side have any > problems with the child functions. > > Because, suppose that they wouldn't like those functions at all. What are we > supposed to do, then, honestly? Add the whole DT vs ACPI logic to the leds-gpio > and gpio_keys_polled drivers? But these drivers have no reason whatsoever > to include that. Zero. > > So suggestions welcome. > > [BTW, In principle we also could use something like > > typedef union dev_node { > struct acpi_device *acpi_node; > struct device_node *of_node; > } dev_node_t; > > instead of the (void *) for more type safety. It still is useful to pass the > parent pointer along with that, though.] > > > > 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. > > That certainly is doable, although the resulting macro would generate a rather > large chunk of code each time it is used. On a second thought I'm not so sure, because we need to iterate either this way or that way depending on a condition evaluated at run time. I have no idea how to do that in a macro at the moment. -- I speak only for myself. Rafael J. Wysocki, Intel Open Source Technology Center.