linux-kernel - Re: [Patch v3 3/9] dt-bindings: arm: tegra: Add NVIDIA Tegra194 axi2apb binding

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Date:   Thu, 23 Dec 2021 13:54:14 +0530
From:   Sumit Gupta <sumitg@...dia.com>
To:     Rob Herring <robh@...nel.org>
CC:     <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <kbuild-all@...ts.01.org>,
        <bbasu@...dia.com>, <vsethi@...dia.com>, <jsequeira@...dia.com>,
        Thierry Reding <treding@...dia.com>,
        Sumit Gupta <sumitg@...dia.com>
Subject: Re: [Patch v3 3/9] dt-bindings: arm: tegra: Add NVIDIA Tegra194
 axi2apb binding



> On Tue, Dec 21, 2021 at 06:21:11PM +0530, Sumit Gupta wrote:
>> Add device-tree binding documentation to represent the axi2apb bridges
>> used by Control Backbone (CBB) 1.0 in Tegra194 SOC. All errors for APB
>> slaves are reported as slave error because APB bas single bit to report
>> error. So, CBB driver needs to further check error status registers of
>> all the axi2apb bridges to find error type.
>>
>> Signed-off-by: Sumit Gupta <sumitg@...dia.com>
>> Signed-off-by: Thierry Reding <treding@...dia.com>
>> ---
>>   .../arm/tegra/nvidia,tegra194-axi2apb.yaml    | 40 +++++++++++++++++++
>>   1 file changed, 40 insertions(+)
>>   create mode 100644 Documentation/devicetree/bindings/arm/tegra/nvidia,tegra194-axi2apb.yaml
>>
>> diff --git a/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra194-axi2apb.yaml b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra194-axi2apb.yaml
>> new file mode 100644
>> index 000000000000..788a13f8aa93
>> --- /dev/null
>> +++ b/Documentation/devicetree/bindings/arm/tegra/nvidia,tegra194-axi2apb.yaml
>> @@ -0,0 +1,40 @@
>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>> +%YAML 1.2
>> +---
>> +$id: "http://devicetree.org/schemas/arm/tegra/nvidia,tegra194-axi2apb.yaml#"
>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>> +
>> +title: NVIDIA Tegra194 AXI2APB bridge
>> +
>> +maintainers:
>> +  - Sumit Gupta <sumitg@...dia.com>
>> +
>> +properties:
>> +  $nodename:
>> +    pattern: "^axi2apb@([0-9a-f]+)$"
>> +
>> +  compatible:
>> +    enum:
>> +      - nvidia,tegra194-axi2apb
>> +
>> +  reg:
>> +    maxItems: 6
>> +    description: Physical base address and length of registers for all bridges
>> +
>> +additionalProperties: false
>> +
>> +required:
>> +  - compatible
>> +  - reg
>> +
>> +examples:
>> +  - |
>> +    axi2apb: axi2apb@...0000 {
> 
> As axi2apb appears to be a bus, then all the child nodes (APB devices)
> should be under this node.

axi2apb is a bridge which coverts an AXI to APB interface and not a bus.
CBB stretches to the various partitions using different bridges like 
axi2apb, axip2p etc connected either as single or in chain.
The bridge reports if error and that gets logged in NOC's error logger.
For APB slaves, all errors are logged as slave errors as there is a 
single error bit. So, we need to read the error status register of the 
bridges to further triage the reason of the error.

> 
> Is NVidia still putting all the devices at the root level rather than
> under a bus node which is preferred?
All the cbb noc nodes in T194 and fabric nodes in T234 are under "bus@0" 
node.

> 
>> +      compatible = "nvidia,tegra194-axi2apb";
>> +      reg = <0x02390000 0x1000>,
>> +            <0x023a0000 0x1000>,
>> +            <0x023b0000 0x1000>,
>> +            <0x023c0000 0x1000>,
>> +            <0x023d0000 0x1000>,
>> +            <0x023e0000 0x1000>;
>> +    };
>> --
>> 2.17.1
>>
>>