Message-ID: <a0713a10-3409-4401-e612-0a9c06f88ea1@canonical.com>
Date:   Wed, 10 Nov 2021 08:43:20 +0100
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Subject: Re: [PATCH 06/13] dt-bindings: rng: add bindings for microchip mpfs
 rng
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To:     Conor.Dooley@microchip.com
Cc:     broonie@kernel.org, aou@eecs.berkeley.edu, robh+dt@kernel.org,
        linus.walleij@linaro.org, bgolaszewski@baylibre.com,
        palmer@dabbelt.com, paul.walmsley@sifive.com,
        jassisinghbrar@gmail.com, atish.patra@wdc.com,
        Daire.McNamara@microchip.com, Lewis.Hanly@microchip.com,
        linux-kernel@vger.kernel.org, devicetree@vger.kernel.org,
        geert@linux-m68k.org, linux-gpio@vger.kernel.org,
        linux-riscv@lists.infradead.org, linux-crypto@vger.kernel.org,
        linux-usb@vger.kernel.org, bin.meng@windriver.com,
        linux-i2c@vger.kernel.org, alexandre.belloni@bootlin.com,
        Ivan.Griffin@microchip.com, linux-rtc@vger.kernel.org,
        linux-spi@vger.kernel.org, a.zummo@towertech.it,
        gregkh@linuxfoundation.org
References: <20211108150554.4457-1-conor.dooley@microchip.com>
 <20211108150554.4457-7-conor.dooley@microchip.com>
 <f60cf7e0-4f67-f4b3-2596-01114cff6623@canonical.com>
 <71c6917e-1463-c708-550a-726e5fe1566d@microchip.com>
 <ca17d6ac-ef8e-b01c-3278-7cbb0d5745e3@canonical.com>
 <ea871add-bddc-c4ae-ac9d-e86b4fad5a02@microchip.com>
From:   Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
In-Reply-To: <ea871add-bddc-c4ae-ac9d-e86b4fad5a02@microchip.com>
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Precedence: bulk

On 09/11/2021 14:36, Conor.Dooley@microchip.com wrote:
> On 09/11/2021 12:56, Krzysztof Kozlowski wrote:
>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>
>> On 09/11/2021 13:54, Conor.Dooley@microchip.com wrote:
>>> On 08/11/2021 21:16, Krzysztof Kozlowski wrote:
>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
>>>>
>>>> On 08/11/2021 16:05, conor.dooley@microchip.com wrote:
>>>>> From: Conor Dooley <conor.dooley@microchip.com>
>>>>>
>>>>> Add device tree bindings for the hardware rng device accessed via
>>>>> the system services on the Microchip PolarFire SoC.
>>>>>
>>>>> Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
>>>>> ---
>>>>>    .../bindings/rng/microchip,mpfs-rng.yaml      | 31 +++++++++++++++++++
>>>>>    1 file changed, 31 insertions(+)
>>>>>    create mode 100644 Documentation/devicetree/bindings/rng/microchip,mpfs-rng.yaml
>>>>>
>>>>> diff --git a/Documentation/devicetree/bindings/rng/microchip,mpfs-rng.yaml b/Documentation/devicetree/bindings/rng/microchip,mpfs-rng.yaml
>>>>> new file mode 100644
>>>>> index 000000000000..e8ecb3538a86
>>>>> --- /dev/null
>>>>> +++ b/Documentation/devicetree/bindings/rng/microchip,mpfs-rng.yaml
>>>>> @@ -0,0 +1,31 @@
>>>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>>>> +%YAML 1.2
>>>>> +---
>>>>> +$id: "http://devicetree.org/schemas/rng/microchip,mpfs-rng.yaml#"
>>>>> +$schema: "http://devicetree.org/meta-schemas/core.yaml#"
>>>>> +
>>>>> +title: Microchip MPFS random number generator
>>>>> +
>>>>> +maintainers:
>>>>> +  - Conor Dooley <conor.dooley@microchip.com>
>>>>> +
>>>>> +properties:
>>>>> +  compatible:
>>>>> +    const: microchip,polarfire-soc-rng
>>>>> +
>>>>> +  syscontroller:
>>>>> +    maxItems: 1
>>>>> +    description: name of the system controller device node
>>>>
>>>> There are several issues with this:
>>>> 1. You need to describe the type.
>>>> 2. Description is not helpful (just copying the name of property) and
>>>> actually misleading because you do not put there the name of device node.
>>>> 3. What is it? Looks like syscon (or sometimes called sysreg). If yes,
>>>> please use existing syscon bindings.
>>> 1 & 2 - Correct, it is bad & I'll write a better description for it.
>>> 3 - Its a system controller implemented as a mailbox. The syscontroller
>>> is the mailbox client, which the rng and generic drivers both use.
>>
>> I understood that pointed device node is a mailbox, not this node. But
>> here, what is it here? How do you use it here?
> The system controller is the means of access to the random number 
> generator. The phandle to the sys controller is provided here so that 
> the rng driver can locate the mailbox client through which it requests 
> random numbers.

I am asking this to understand whether there is a generic or existing
property which should be used instead.

If I understand correctly, the rng driver needs a mailbox client?  If it
is mailbox client, then there is a property: "mboxes". Use this one
(look for existing bindings, e.g.
Documentation/devicetree/bindings/firmware/arm,scmi.yaml).


Best regards,
Krzysztof