On Fri, 01 Nov 2013 15:27:34 +1100 Benjamin Herrenschmidt <benh@xxxxxxxxxxxxxxxxxxx> wrote: > On Fri, 2013-11-01 at 15:22 +1100, Benjamin Herrenschmidt wrote: > > On Fri, 2013-11-01 at 14:59 +1100, NeilBrown wrote: > > > and I wonder how relevant it still is in this context. As platform devices > > > are all in the root of the device-tree and hence are siblings, they must have > > > unique names in the device-tree and so the platform devices created from > > > them will also have unique names -- won't they? > > > > I agree about /sys/devices -> /sys/devices/platform, that makes more > > sense > > > > The problem with names is that we don't *know* that your devices are > > at the root and unique. They don't have to be. I have platforms that > > have several "chips" each containing all the same devices. They need to > > be de-duped. > > > > Maybe the right approach is to build the de-duplication in sysfs > > itself ? Do you mean we could allow multiple devices on the one bus to have the same name, but get sysfs to notice and de-duplicate by mangling one name? I don't think I like that but I might have misunderstood. 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" ?? Hoping someone who understands the device model better than me will help. > > BTW. How come you have devices at the root of the tree without "reg" ? > It's fairly fishy ... > > The root of the tree is supposed to represent the processor address > space, and has #address-cells/#size-cells set appropriately. Any MMIO > mapped device shall thus have a "reg" property and a unit address. > > Only "container" nodes (such as /cpus or /chosen) or virtual devices > (such as a node used to representing the collection of bits & pieces > that makes the audio infrastructure) and are thus not per-se MMIO mapped > entities can ommit the "reg" properties. > > In the case of pwm, it looks like there's another device providing a pwm > capability, in which case your backlight would indeed be a "virtual > device" (basically non-mmio device not hanging off any bus). Or it could > have been represented as a child of pwm if that had been defined that > way, I am not familiar with the pwm bindings. The 'backlight' device is a virtual device. It uses a 'pwm' device to provide the variable brightness to the back light. The 'pwm' device itself is virtual, making use of a 'dmtimer' to provide the timing... The timer device (timer11 in omap3.dtsi) has a 'reg' property. A random example from current mainline is arch/arm/boot/dts/am335x-evmsk.dts which has 'backlight' as a virtual device compatible with pwm-backlight. It also has 'gpio-keys', 'gpio-leds', and 'regulator-fixed' compatible virtual devices. They seem fairly common. Thanks, NeilBrown > > Cheers, > Ben. > > > Cheers, > > Ben. > > > > > Any help understanding and/or fixing this discrepancy greatly appreciated. > > > > > > The change of name is particularly annoying to me because one of my platform > > > devices is a pwm_bl.c backlight. With a boardfile I > > > get /sys/class/pwm_backlight. With devicetree the best I can get > > > is /sys/class/pwm_backlight.23 (or similar). It would be really nice to have > > > a more stable and sensible name here. > > >
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