[PATCH 2/3] dt-bindings: allow child nodes inside the Tegra BPMP

[Stephen Warren]

On 07/26/2016 04:03 AM, Thierry Reding wrote:
> On Tue, Jul 19, 2016 at 01:14:41PM -0600, Stephen Warren wrote:
>> From: Stephen Warren <swarren at nvidia.com>
>>
>> The BPMP implements some services which must be represented by separate
>> nodes. For example, it can provide access to certain I2C controllers, and
>> the I2C bindings represent each I2C controller as a device tree node.
>> Update the binding to describe how the BPMP supports this.
>>
>> Signed-off-by: Stephen Warren <swarren at nvidia.com>
>> ---
>>  .../bindings/firmware/nvidia,tegra186-bpmp.txt     | 23 ++++++++++++++++++++++
>>  1 file changed, 23 insertions(+)
>>
>> diff --git a/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt b/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt
>> index 9a3864f56955..142d363406f6 100644
>> --- a/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt
>> +++ b/Documentation/devicetree/bindings/firmware/nvidia,tegra186-bpmp.txt
>> @@ -38,6 +38,24 @@ implemented by this node:
>>  - .../reset/reset.txt
>>  - <dt-bindings/reset/tegra186-reset.h>
>>
>> +The BPMP implements some services which must be represented by separate nodes.
>> +For example, it can provide access to certain I2C controllers, and the I2C
>> +bindings represent each I2C controller as a device tree node. Such nodes should
>> +be nested directly inside the main BPMP node.
>> +
>> +Software can determine whether a child node of the BPMP node represents a device
>> +by checking for a compatible property. Any node with a compatible property
>> +represents a device that can be instantiated. Nodes without a compatible
>> +property may be used to provide configuration information regarding the BPMP
>> +itself, although no such configuration nodes are currently defined by this
>> +binding.
>> +
>> +The BPMP firmware defines no single global name-/numbering-space for such
>> +services. Put another way, the numbering scheme for I2C buses is distinct from
>> +the numbering scheme for any other service the BPMP may provide (e.g. a future
>> +hypothetical SPI bus service). As such, child device nodes will have no reg
>> +property, and the BPMP node will have no #address-cells or #size-cells property.
>
> My understanding is that the I2C bus number is passed as part of the
> request to the BPMP firmware. Does that not count as addressing? Could
> we not represent that generically using a device tree hierarchy? I'm
> thinking something along these lines:
>
> 	bpmp {
> 		...
>
> 		services {
> 			i2c {
> 				i2c at 0 {
> 					reg = <0>;

Technically, that is possible. However, Rob Herring rejected the idea of 
multiple levels of sub-nodes.

Can we please just go with what we have? DT bindings are frankly an 
obstacle to getting anything done:-(