From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751983AbaKEUjO (ORCPT ); Wed, 5 Nov 2014 15:39:14 -0500 Received: from v094114.home.net.pl ([79.96.170.134]:61762 "HELO v094114.home.net.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1750702AbaKEUjH (ORCPT ); Wed, 5 Nov 2014 15:39:07 -0500 From: "Rafael J. Wysocki" To: Darren Hart Cc: Grant Likely , Mika Westerberg , Alexandre Courbot , Linus Walleij , Arnd Bergmann , ACPI Devel Mailing List , Linux Kernel Mailing List Subject: Re: [PATCH] ACPI / GPIO: Pass index to acpi_get_gpiod_by_index() when using properties Date: Wed, 05 Nov 2014 21:59:51 +0100 Message-ID: <2251117.W1kfIOl2SD@vostro.rjw.lan> User-Agent: KMail/4.11.5 (Linux/3.16.0-rc5+; KDE/4.11.5; x86_64; ; ) In-Reply-To: <5459646E.9000707@linux.intel.com> References: <1414494927-204923-1-git-send-email-mika.westerberg@linux.intel.com> <3196606.Sy6xFg88zg@vostro.rjw.lan> <5459646E.9000707@linux.intel.com> 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 Tuesday, November 04, 2014 03:42:38 PM Darren Hart wrote: > > On 11/4/14 14:54, Rafael J. Wysocki wrote: > > > From: Rafael J. Wysocki > > Subject: ACPI / property: Drop size_prop from acpi_dev_get_property_reference() > > > > The size_prop argument of the recently added function > > acpi_dev_get_property_reference() is not used by the only current > > caller of that function and is very unlikely to be used at any time > > going forward. > > > > Namely, for a property whose value is a list of items each containing > > a references to a device object possibly accompanied by some integers, > > the number of items in the list can always be computed as the number > > of elements of type ACPI_TYPE_LOCAL_REFERENCE in the property package. > > Thus it should never be necessary to provide an additional "cells" > > property with a value equal to the number of items in that list. > > In this case, do we never expect a property to contain more than one > ACPI_TYPE_LOCAL_REFERENCE? > > Package () { "foobar", > Package () { > "PCI0.FOO", "PCI0.BAR", 0, 1, 0, > "PCI0.FOO", "PCI0.BAR2", 0, 1, 1 > } > } > > This seems like it could be useful for connecting various types of > devices together, but I confess not to have a specific exmaple in mind. > It does concern me to limit the data format in this way. We don't support this even with size_prop, so it doesn't seem to be relevant here. Now, if we were to support this, I'd rather not use acpi_dev_get_property_reference() for that, but add a new function specifically for it. Moreover, I would extend the format definition then so that we could do Package () { "foobar", Package () { Package () {"PCI0.FOO", "PCI0.BAR", 0, 1, 0}, Package () {"PCI0.FOO", "PCI0.BAR2", 0, 1, 1} } } in which case adding a special "size" property could be avoided. That said, I have no idea why it might be necessary. One reference in a property value means that we're connecting the current node (the owner of the _DSD containing that property) with some other node in the namespace. Two references in there would mean that the current node is to be connected with *two* other nodes in the namespace at the same time. That raises some questions that I'd rather not consider in detail here, unless you insist. ;-) > I suppose should such a case become necessary, we can deal with the > issue then - and still avoid having a potential abuse point in the API > from the start. What we have today is sufficient for all of the cases we've considered so far. If we find a case where it is not sufficient, we'll need to consider extending the data format as well as the API. Rafael