Re: [PATCH v2 1/3] dt-bindings: Add YAML bindings for Host1x and NVDEC

On Tue, Aug 10, 2021 at 06:50:26PM +0300, Mikko Perttunen wrote:

On 10.8.2021 18.43, Thierry Reding wrote:

quoted

On Fri, Aug 06, 2021 at 03:34:48PM +0300, Mikko Perttunen wrote:

quoted

Convert the original Host1x bindings to YAML and add new bindings for
NVDEC, now in a more appropriate location. The old text bindings
for Host1x and engines are still kept at display/tegra/ since they
encompass a lot more engines that haven't been converted over yet.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
---
v2:
* Fix issues pointed out in v1
* Add T194 nvidia,instance property
---
  .../gpu/host1x/nvidia,tegra20-host1x.yaml     | 131 ++++++++++++++++++
  .../gpu/host1x/nvidia,tegra210-nvdec.yaml     | 109 +++++++++++++++
  MAINTAINERS                                   |   1 +
  3 files changed, 241 insertions(+)
  create mode 100644 Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra20-host1x.yaml
  create mode 100644 Documentation/devicetree/bindings/gpu/host1x/nvidia,tegra210-nvdec.yaml

Can we split off the NVDEC bindings addition into a separate patch? I've
been working on converting the existing host1x bindings in full to json-
schema and this partial conversion would conflict with that effort.

I assume that NVDEC itself validates properly even if host1x hasn't been
converted yet?

Sure. I thought I had some problems with this before but can't see any now.

quoted

quoted

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..fc535bb7aee0
--- /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@gmail.com>
+  - Mikko Perttunen <mperttunen@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: read2

The convention that we've used so far has been to start numbering these
at 0 and use a dash, so this would be "read-1".

Will fix.

quoted

quoted

+      - const: write
+
+required:
+  - compatible
+  - reg
+  - clocks
+  - clock-names
+  - resets
+  - reset-names
+  - power-domains
+
+if:
+  properties:
+    compatible:
+      contains:
+        const: nvidia,tegra194-host1x
+then:
+  properties:
+    nvidia,instance:
+      items:
+        - description: 0 for NVDEC0, or 1 for NVDEC1

I know we had discussed this before, but looking at the driver patch, I
don't actually see this being used now, so I wonder if we still need it.

quoted

+additionalProperties: true

Maybe this should have a comment noting that this should really be
unevaluatedProperties: false, but we can't use that because the tooling
doesn't support it yet?

I can add such a comment if desired. Honestly, I don't really know what
'unevaluatedProperties' means or does -- the explanation in
example-schema.yaml doesn't seem like it's relevant here and I cannot find
any other documentation.

It's basically like additionalProperties, except that it applies to
properties evaluated via if: blocks.

So with additionalProperties: false, the presence of the nvidia,instance
property in a Tegra194 DTS file would cause a validation failure because
it's a property that was not defined in the properties: block.

With unevaluatedProperties: false, on the other hand, the properties
that are defined in the if: block above will become a evaluated
properties and therefore a Tegra194 DTS with the nvidia,instance
property present would succeed validation. Unless, of course, if it
contained additional properties that are not defined in any of the
properties: blocks (either unconditional or conditional ones).

So in other words, the additionalProperties schema applies to all
unconditionally defined properties, whereas unevaluatedProperties
applies to all (conditionally and unconditionally) defined properties.

Thierry