Describing devices in the device tree

Describing devices in the device tree

[Alan Bennett]

I'm using a modified ep8248e.dts to describe my hardware and I want to
enable the use of 3 standard interrupts.

  1. irq5
  2. timer1
  3. timer2

How bad does this look?
soc --> cpm -->
                       timer {
                               device_type = "timer";
                               compatible = "fsl,mpc8248-timer";
                               interrupts = <c 8 d 8>;
                               interrupt-parent = <&PIC>;
                       };
                       irq5 {
                               device_type = "irq5";
                               compatible = "fsl,mpc8248-irq5";
                               interrupts = <17 8>;
                               interrupt-parent = <&PIC>;
                       };

-Alan

Re: Describing devices in the device tree

[Grant Likely]

On 10/16/07, Alan Bennett <embedded@akb.net> wrote:
> I'm using a modified ep8248e.dts to describe my hardware and I want to
> enable the use of 3 standard interrupts.
>
>   1. irq5
>   2. timer1
>   3. timer2
>
> How bad does this look?
> soc --> cpm -->
>                        timer {
>                                device_type = "timer";
>                                compatible = "fsl,mpc8248-timer";
>                                interrupts = <c 8 d 8>;
>                                interrupt-parent = <&PIC>;
>                        };
>                        irq5 {
>                                device_type = "irq5";
>                                compatible = "fsl,mpc8248-irq5";
>                                interrupts = <17 8>;
>                                interrupt-parent = <&PIC>;
>                        };

Don't do this.  Instead, describe the device that generates the
interrupt.  You don't need the device_type property either unless it
is a common device.  The compatible property should also describe your
device; not the irq line.

Just creating a device node to describe an irq line doesn't buy you
anything because your device driver still needs to have the knowledge
built into it to use IRQ5.  You may as well have just hard coded the
value into your driver instead of traversing through the device tree
to get it.

You get an advantage when you create a node for you *device* that your
device driver can bind, and embed into that node the IRQ line that it
uses.

Cheers,
g.

-- 
Grant Likely, B.Sc., P.Eng.
Secret Lab Technologies Ltd.
grant.likely@secretlab.ca
(403) 399-0195