[PATCH v4 1/3] dt-bindings: Add YAML bindings for NVDEC

[Mikko Perttunen]

On 9/3/21 7:34 PM, Rob Herring wrote:
> On Fri, Sep 03, 2021 at 11:31:53AM +0300, Mikko Perttunen wrote:
>> Add YAML device tree bindings for NVDEC, now in a more appropriate
>> place compared to the old textual Host1x bindings.
>>
>> Signed-off-by: Mikko Perttunen <mperttunen at nvidia.com>
>> ---
>> v4:
>> * Fix incorrect compatibility string in 'if' condition
>> v3:
>> * Drop host1x bindings
>> * Change read2 to read-1 in interconnect names
>> v2:
>> * Fix issues pointed out in v1
>> * Add T194 nvidia,instance property
>> ---
>>   .../gpu/host1x/nvidia,tegra210-nvdec.yaml     | 109 ++++++++++++++++++
>>   MAINTAINERS                                   |   1 +
>>   2 files changed, 110 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra210-nvdec.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra210-nvdec.yaml b/Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra210-nvdec.yaml
>> new file mode 100644
>> index 000000000000..33d01c7dc759
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra210-nvdec.yaml
>> @@ -0,0 +1,109 @@
>> +# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: "http://devicetree.org/schemas/gpu/host1x/nvidia,tegra210-nvdec.yaml#"
>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>> +
>> +title: Device tree binding for NVIDIA Tegra NVDEC
>> +
>> +description: |
>> +  NVDEC is the hardware video decoder present on NVIDIA Tegra210
>> +  and newer chips. It is located on the Host1x bus and typically
>> +  programmed through Host1x channels.
>> +
>> +maintainers:
>> +  - Thierry Reding <treding at gmail.com>
>> +  - Mikko Perttunen <mperttunen at nvidia.com>
>> +
>> +properties:
>> +  $nodename:
>> +    pattern: "^nvdec@[0-9a-f]*$"
>> +
>> +  compatible:
>> +    enum:
>> +      - nvidia,tegra210-nvdec
>> +      - nvidia,tegra186-nvdec
>> +      - nvidia,tegra194-nvdec
>> +
>> +  reg:
>> +    maxItems: 1
>> +
>> +  clocks:
>> +    maxItems: 1
>> +
>> +  clock-names:
>> +    items:
>> +      - const: nvdec
>> +
>> +  resets:
>> +    maxItems: 1
>> +
>> +  reset-names:
>> +    items:
>> +      - const: nvdec
>> +
>> +  power-domains:
>> +    maxItems: 1
>> +
>> +  iommus:
>> +    maxItems: 1
>> +
>> +  interconnects:
>> +    items:
>> +      - description: DMA read memory client
>> +      - description: DMA read 2 memory client
>> +      - description: DMA write memory client
>> +
>> +  interconnect-names:
>> +    items:
>> +      - const: dma-mem
>> +      - const: read-1
>> +      - const: write
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +  - clocks
>> +  - clock-names
>> +  - resets
>> +  - reset-names
>> +  - power-domains
>> +
>> +if:
>> +  properties:
>> +    compatible:
>> +      contains:
>> +        const: nvidia,tegra194-nvdec
>> +then:
>> +  properties:
>> +    nvidia,instance:
>> +      items:
>> +        - description: 0 for NVDEC0, or 1 for NVDEC1
> 
> I still don't understand what this is needed for. What is the difference
> between the instances? There must be some reason you care. We should
> describe that difference, not some made up index.
> 
> I'm not suggesting using the base address either. That's fragile too.

This device is on the Host1x bus. On that bus, each device has an 
identifier baked into hardware called 'class' that is used when 
accessing devices through some mechanisms (host1x channels). As such, 
when probing the device we need to specify the class of the device to 
the host1x driver so it knows how to talk to it. Those class numbers are 
fixed so we have hardcoded them in the driver, but now that we have two 
NVDECs, we need to distinguish between them so that we can specify the 
correct class for each instance to the host1x driver.

> 
>> +
>> +additionalProperties: true
> 
> 'true' here is not allowed unless the schema is not complete and
> intended to be included in a complete schema or unconditionally applied
> (i.e. 'select: true'). This case is neither. As pointed out previously,
> 'unevaluatedProperties' is what you'd want here.
> 
> However, I looked into supporting defining properties in if/then/else
> schemas as you have done and I don't think we will support that soon.
> It's problematic because we can't validate the schema under the if/then
> completely. The reason is properties under if/then schemas don't have to
> be complete as we expect a top level definition that is complete (e.g.
> vendor properties must have 'description'). To solve this, we'd have to
> only apply meta-schema checks if the property doesn't appear at the top
> level. That's more complicated than I care to implement ATM.

I see two paths here: either keep 'additionalProperties: true' or remove 
it and have this binding trigger validation failures. Which one do you 
suggest or is there some third option?

Thanks,
Mikko

> 
> Rob
>