linux-kernel - Re: [PATCH v3 2/4] dt-bindings: memory: tegra20: emc: Document new LPDDR2 sub-node

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Message-ID: <a3713f62-0ece-5ab2-f55a-3d614ce01c00@canonical.com>
Date:   Mon, 4 Oct 2021 10:37:11 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Jonathan Hunter <jonathanh@...dia.com>,
        Rob Herring <robh+dt@...nel.org>
Cc:     devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-tegra@...r.kernel.org
Subject: Re: [PATCH v3 2/4] dt-bindings: memory: tegra20: emc: Document new
 LPDDR2 sub-node

On 03/10/2021 03:32, Dmitry Osipenko wrote:
> Some Tegra20 boards don't have RAM code stored in NVMEM, which is used for
> the memory chip identification and the identity information should be read
> out from LPDDR2 chip in this case. Document new sub-node containing generic
> LPDDR2 properties that will be used for the memory chip identification if
> RAM code isn't available. The identification is done by reading out memory
> configuration values from generic LPDDR2 mode registers of SDRAM chip and
> comparing them with the values of device-tree sub-node's.
> 
> Signed-off-by: Dmitry Osipenko <digetx@...il.com>
> ---
>  .../memory-controllers/nvidia,tegra20-emc.yaml  | 17 ++++++++++++++---
>  1 file changed, 14 insertions(+), 3 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-emc.yaml b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-emc.yaml
> index cac6842dc8f1..65f7c3898ac4 100644
> --- a/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-emc.yaml
> +++ b/Documentation/devicetree/bindings/memory-controllers/nvidia,tegra20-emc.yaml
> @@ -164,13 +164,14 @@ patternProperties:
>        "#size-cells":
>          const: 0
>  
> +      lpddr2-configuration:

Nodes should be named generic, so just lpddr2?


> +        $ref: "jedec,lpddr2.yaml#"
> +        type: object
> +
>      patternProperties:
>        "^emc-table@[0-9]+$":
>          $ref: "#/$defs/emc-table"
>  
> -    required:
> -      - nvidia,ram-code

Isn't lpddr2-configuration required in such case? If not, probably you
want either this or that (oneOf like in reserved-memory.yaml).

> -
>      additionalProperties: false
>  
>  required:
> @@ -186,6 +187,8 @@ additionalProperties: false
>  
>  examples:
>    - |
> +    #include <dt-bindings/memory/lpddr2.h>
> +
>      external-memory-controller@...0f400 {
>          compatible = "nvidia,tegra20-emc";
>          reg = <0x7000f400 0x400>;
> @@ -226,5 +229,13 @@ examples:
>                          0x007fe010 0x00001414 0x00000000 0x00000000
>                          0x00000000 0x00000000 0x00000000 0x00000000>;
>              };
> +
> +            lpddr2-configuration {
> +                jedec,lpddr2-manufacturer-id = <LPDDR2_MANID_ELPIDA>;
> +                jedec,lpddr2-revision-id1 = <1>;
> +                jedec,lpddr2-density-mbits = <2048>;
> +                jedec,lpddr2-io-width-bits = <16>;
> +                jedec,lpddr2-type = <LPDDR2_TYPE_S4>;
> +            };
>          };
>      };
> 


Best regards,
Krzysztof