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Date: Fri, 15 Nov 2013 16:44:16 +0900 From: Grant Likely <grant.likely@...aro.org> To: NeilBrown <neilb@...e.de>, Benjamin Herrenschmidt <benh@...nel.crashing.org> Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Rob Herring <rob.herring@...xeda.com>, devicetree@...r.kernel.org, lkml <linux-kernel@...r.kernel.org> Subject: Re: Strange location and name for platform devices when device-tree is used. On Sat, 2 Nov 2013 10:45:05 +1100, NeilBrown <neilb@...e.de> wrote: > On Sat, 02 Nov 2013 10:10:25 +1100 Benjamin Herrenschmidt > <benh@...nel.crashing.org> 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. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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