From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752876Ab3KOPFe (ORCPT ); Fri, 15 Nov 2013 10:05:34 -0500 Received: from mail-we0-f171.google.com ([74.125.82.171]:37822 "EHLO mail-we0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752350Ab3KOPEd (ORCPT ); Fri, 15 Nov 2013 10:04:33 -0500 From: Grant Likely Subject: Re: Strange location and name for platform devices when device-tree is used. To: NeilBrown , Benjamin Herrenschmidt Cc: Greg Kroah-Hartman , Rob Herring , devicetree@vger.kernel.org, lkml In-Reply-To: <20131102104505.34105cbb@notabene.brown> References: <20131101145925.66e22f73@notabene.brown> <1383279744.28909.26. camel@pasglop> <1383280054.28909.30.camel@pasglop> <20131101160329.37f3707b @notabene.brown> <1383282516.28909.36.camel@pasglop> <20131101204749. GA19662@kroah.com> <1383347425.28909.63.camel@pasglop> <20131102104505. 34105cbb@notabene.brown> Date: Fri, 15 Nov 2013 16:44:16 +0900 Message-Id: <20131115074416.4DA8DC40828@trevor.secretlab.ca> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sat, 2 Nov 2013 10:45:05 +1100, NeilBrown wrote: > On Sat, 02 Nov 2013 10:10:25 +1100 Benjamin Herrenschmidt > wrote: > > > On Fri, 2013-11-01 at 13:47 -0700, Greg Kroah-Hartman wrote: > > > > > > > On my device I seem to have some platform devices registered through > > > > > device-tree, and some registered through platform_device_add (e.g. > > > > > 'alarmtimer'). Guaranteeing they remain disjoint sets if the kernel is > > > > > allowed to evolve independently of the devicetree might be tricky.... > > > > > Maybe we need "/sys/devices/platform" and "/sys/devices/dt_platform" ?? > > > > > > > > No, I think device-tree created platform devices should go > > > > to /sys/devices/platform like the "classic" ones. > > > > > > > > The problem is really how to deal with potential name duplication. We > > > > could try to register, if we get -EEXIST (assuming sysfs returns the > > > > right stuff), try again with ".1" etc... > > > > > > How can there be device name collisions? All platform devices _should_ > > > be named uniquely, if not, you have bigger problems... > > > > The problem is how to create a unique name for a platform device created > > from a device-tree node. > > > > Device tree nodes aren't necessarily uniquely named. They are unique > > under a given parent but that hierarchy isn't preserved when creating > > corresponding platform devices (and it would be very tricky to do so). > > > > Currently, we simply append a number to the name when creating them, > > which is obtained from a global counter. > > > > Neil is unhappy about that because on his specific hardware, the device > > has a unique name and thus we introduce a naming difference between > > device-tree usage and old-style "hard coded" board file usage. > > It occurs to me that a different approach could solve my problem. > > My problem stems from the fact that the name of the device on the > platform-bus is used as the name of the device in the "backlight" class. > > As Greg writes elsewhere, depending on names with /sys/devices is not > supported - we need to accept that bus-names might change. > However names in class devices tend to be a lot more stable. > Several devices allow these to be explicitly set. > leds have 'label' > regulators has "regulator-name" > gpio-keys has 'label'. > > I could just teach pwm_bl to allow a 'label' property which would be used in > place of the platform-bus device name when creating the class/backlight > device. > > The maxim "you cannot trust names to remain stable in /sys/devices" can > justify both the movement of platform devices into /sys/devices/platform, and > the use of "label" rather than the device-name for creating the class device. > > Does that sound convincing? The problem with a property in the node in this case is that there is no guarantee of uniqueness. An alternative however would be to look for an alias in /aliases. Those are unique. g.