LED devices

[Kay Sievers]

On Fri, 2007-06-01 at 17:29 +0100, Richard Purdie wrote:
> On Fri, 2007-06-01 at 18:12 +0200, Kay Sievers wrote:
> > On Fri, 2007-06-01 at 16:56 +0100, Richard Purdie wrote:
> > > I've often wished we could do this as it would suit triggers well! The
> > > same approach could be used for bio schedulers and other selection type
> > > operations. As you say its not really possible though and would be more
> > > difficult to use in reality.
> > 
> > I'm not familiar with the whole infrastructure, so I might be on the
> > wrong track. :)
> > 
> > Wouldn't something like the blockdev holders/ slaves/ subdirs work to
> > express such a relationship?
> > 
> >   $ ls -l /sys/block
> >   md0 -> ../devices/virtual/block/md0
> >   sda -> ../devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda
> >   sr0 -> ../devices/pci0000:00/0000:00:1f.1/host4/target4:0:0/4:0:0:0/block/sr0
> > 
> >   $ ls -l  /sys/block/md0/slaves
> >   sda8 -> ../../../../../devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda/sda8
> >   sda9 -> ../../../../../devices/pci0000:00/0000:00:1f.2/host0/target0:0:0/0:0:0:0/block/sda/sda9
> > 
> >   $ ls -l  /sys/block/sda/sda8/holders
> >   md0 -> ../../../../../../../../../../devices/virtual/block/md0
> > 
> > It shows the relationship in both directions, and is not limited to a
> > single relation per device.
> 
> Can userspace trigger a change of this relationship though?

Sure, but there is no standard way of doing it. For the block stuff,
it's done with ioctl's on a control-device-node.

> We need to
> be able to change the trigger an LED is using...
> 
> At the moment the trigger attribute functions
> like /sys/block/*/queue/scheduler:
> 
> # cat /sys/block/sda/queue/scheduler 
> noop anticipatory deadline [cfq]
> 
> # echo "noop" > /sys/block/sda/queue/scheduler 
> 
> # cat /sys/block/sda/queue/scheduler 
> [noop] anticipatory deadline cfq

Yes, a sysfs mechanism will probably work fine for the led stuff.
Similar to the bind/unbind interface at the bus-driver level:
  $ ls -l /sys/bus/usb/drivers/hub/
  1-0:1.0 -> ../../../../devices/pci0000:00/0000:00:1d.0/usb1/1-0:1.0
  2-0:1.0 -> ../../../../devices/pci0000:00/0000:00:1d.1/usb2/2-0:1.0
  3-0:1.0 -> ../../../../devices/pci0000:00/0000:00:1d.2/usb3/3-0:1.0
  bind
  module -> ../../../../module/usbcore
  new_id
  unbind

The bind/unbind files expect the bus-id's of the device, the driver
should bind/unbind.

Kay