[PATCH 2/5] arm: dts: lpc32xx: fix improper usage of ranges property

[Joachim Eastwood]

On 14 October 2015 at 22:07, Arnd Bergmann <arnd at arndb.de> wrote:
> On Wednesday 14 October 2015 19:23:09 Joachim Eastwood wrote:
>> >
>> > /ahb5 {
>> >         ranges = <0 0x20000000 0x10000000>;
>> >
>> >         apb {
>> >                 ranges = <0 0x80000 0x20000>;
>> >         };
>> > };
>> > /ahb6 {
>> >         ranges = <0 0x30000000 0x10000000>,           /* AHB registers */
>> >                  <0x80000000 0x80000000 0x40000000>, /* EMC DYCS0/1 */
>> >                  <0xE0000000 0xE0000000 0x04000000>; /* EMC CS0-3 */
>> >
>> >         memory-controller at 1080000 {
>> >                 reg = <0x1080000 0x10000>;
>> >         };
>> > };
>>
>> Sorry for hijacking the thread, but I have related question to this.
>>
>> What is the advantage of using a hierarchical bus structure in dt?
>> I thought the recommendation, at least for new device trees, was to
>> keep it flat under a "soc"-node.
>>
>> If doesn't offer any advantages why not remove instead of adding the
>> ranges property which seems to grow a bit complex now?
>> Of course removing it would create a lot of churn because of the
>> re-indentation but at least the end result would be simpler.
>
> The general recommendation is to have the DT structure resemble
> the hardware as closely as possible. If the chip has a clear
> hierarchy and you know it, then it's best to describe it that way.
>
> The reason for having a single 'soc' node in a lot of the modern
> dtsi files is that either it's not documented, or they use AXI
> 'buses' that are not really hierarchical but are point-to-point
> connections.

Thanks for explaining, Arnd!

In that case lpc18xx.dtsi should have had a hierarchical structure as
well. NXP LPC user manuals usually documents the bus structure.


regards,
Joachim Eastwood