linux-kernel - Re: [PATCH] dt-bindings: mailbox: mtk-gce: Convert txt to json-schema

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Date:   Tue, 24 May 2022 19:34:34 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>, robh+dt@...nel.org
Cc:     jassisinghbrar@...il.com, krzysztof.kozlowski+dt@...aro.org,
        matthias.bgg@...il.com, houlong.wei@...iatek.com,
        linux-kernel@...r.kernel.org, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH] dt-bindings: mailbox: mtk-gce: Convert txt to json-schema

On 24/05/2022 14:18, AngeloGioacchino Del Regno wrote:
> Il 20/05/22 10:15, Krzysztof Kozlowski ha scritto:
>> On 19/05/2022 12:18, AngeloGioacchino Del Regno wrote:
>>> Convert the mtk-gce documentation from freeform text format to a
>>> json-schema.
>>>
>>> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
>>> ---
>>>   .../bindings/mailbox/mediatek,gce-mbox.yaml   | 114 ++++++++++++++++++
>>>   .../devicetree/bindings/mailbox/mtk-gce.txt   |  82 -------------
>>>   2 files changed, 114 insertions(+), 82 deletions(-)
>>>   create mode 100644 Documentation/devicetree/bindings/mailbox/mediatek,gce-mbox.yaml
>>>   delete mode 100644 Documentation/devicetree/bindings/mailbox/mtk-gce.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/mailbox/mediatek,gce-mbox.yaml b/Documentation/devicetree/bindings/mailbox/mediatek,gce-mbox.yaml
>>> new file mode 100644
>>> index 000000000000..750391b4038c
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/mailbox/mediatek,gce-mbox.yaml
>>> @@ -0,0 +1,114 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/mailbox/mediatek,gce-mbox.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: MediaTek Global Command Engine (GCE) mailbox
>>> +
>>> +maintainers:
>>> +  - Houlong Wei <houlong.wei@...iatek.com>
>>> +
>>> +description: |
>>> +  The Global Command Engine (GCE) is used to help read/write registers
>>> +  with critical time limitation, such as updating display configuration
>>> +  during the vblank.
>>> +  The GCE can be used to implement the Command Queue (CMDQ) driver.
>>
>> Mention the headers in description.
>>
> 
>    Values for properties used by the GCE, such as sub-system IDs, thread
> 
>    priority and event IDs are defined in 'dt-bindings/gce/<chip>-gce.h'.
> 
> Would that be enough, or should I list all of the headers?

Yes.

> 
>>> +
>>> +properties:
>>> +  compatible:
>>> +    enum:
>>> +      - mediatek,mt6779-gce
>>> +      - mediatek,mt8173-gce
>>> +      - mediatek,mt8183-gce
>>> +      - mediatek,mt8186-gce
>>> +      - mediatek,mt8192-gce
>>> +      - mediatek,mt8195-gce
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 1
>>> +
>>> +  clock-names:
>>> +    items:
>>> +      - const: gce
>>> +
>>> +  '#mbox-cells':
>>> +    description: |
>>> +      The first cell describes the mailbox channel, which is the GCE Thread ID;
>>> +      The second cell describes the priority of the GCE thread.
>>> +    const: 2
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg
>>> +  - interrupts
>>> +  - clocks
>>> +  - clock-names
>>> +  - '#mbox-cells'
>>> +
>>> +additionalProperties: false
>>> +
>>> +allOf:
>>> +  - if:
>>> +      properties:
>>> +        compatible:
>>> +          enum:
>>> +            - mediatek,mt8195-gce
>>> +    then:
>>> +      properties:
>>> +        clocks:
>>> +          maxItems: 2
>>
>> Are you sure this works on mt8195-gce?
>>
> 
> Thanks for that, I've just rechecked the driver and.. no, that won't
> work for MT8195: it's just one clock there (like the others) and the
> clock names aren't even enforced, as the driver is always taking the
> clock at index 0.

I was not thinking about driver, although it's nice that my review
helped in that. What I was mentioning, is your bindings behave correctly
for mediatek,mt8195-gce DTS? You have maxItems:1 and maxItems:2, so
usually it was failing, AFAIR.

The same with clock-names - I think the schema should fail here.


> 
> I got confused because the driver uses a slightly different kind of
> logic when probing on SoCs with multiple mailboxes, specifically:
>   - For single mailbox, having a clock with name "gce" is enforced
>     as it's grabbing it with devm_clk_get(dev, clk_name), where the
>     clock name is declared in a string called "clk_name";
>   - For multiple mailboxes, it's looking for an of_alias, declared
>     in an array of strings called "clk_names" and getting the clock
>     with of_clk_get(node, 0).
> 
> 
> So there comes my confusion, recapping:
> 
> static const char * const clk_name = "gce";
>                   <- this is a clock name
> static const char * const clk_names[] = { "gce0", "gce1" }; <- OF alias names
> 
> 
> At this point, I think that the best idea would be to fix this issue
> first... luckily there's no MT8195 devicetree upstream yet, so I would
> technically not be breaking any ABI by changing it to be the same as
> the others.

All this sounds a bit unrelated to the bindings. Anyway, gce for one
case and gce0+gce1 for other, are okay, although schema looks a bit more
complicated. See for example:
https://lore.kernel.org/linux-devicetree/20220523181836.2019180-8-dmitry.baryshkov@linaro.org/

Best regards,
Krzysztof