Re: Strange location and name for platform devices whendevice-tree is used.
From: Benjamin Herrenschmidt
Date: Fri Nov 01 2013 - 01:09:20 EST
On Fri, 2013-11-01 at 16:03 +1100, NeilBrown wrote:
> 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.
What other option do we have ?
> 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...
> Hoping someone who understands the device model better than me will help.
Greg ? :-)
> 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
> 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.
> > 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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