On Sat, 02 Nov 2013 10:10:25 +1100 Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> 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? Thanks, NeilBrown > > It would be nice if we could do something that only appends the "global > number" at the end of the name if the name isn't already unique. Thus my > proposal of trying first with the base name, and trying again if that > returns -EEXIST in some kind of loop. > > Do you have a better idea ? > > Cheers, > Ben. >
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