linux-kernel - Re: [PATCH 06/13] dt-bindings: rng: add bindings for microchip mpfs rng

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Message-ID: <9d6f2e66-860c-2b8a-0b45-7dc56dd5298f@microchip.com>
Date:   Wed, 10 Nov 2021 09:46:23 +0000
From:   <Conor.Dooley@...rochip.com>
To:     <krzysztof.kozlowski@...onical.com>
CC:     <broonie@...nel.org>, <aou@...s.berkeley.edu>,
        <robh+dt@...nel.org>, <linus.walleij@...aro.org>,
        <bgolaszewski@...libre.com>, <palmer@...belt.com>,
        <paul.walmsley@...ive.com>, <jassisinghbrar@...il.com>,
        <atish.patra@....com>, <Daire.McNamara@...rochip.com>,
        <Lewis.Hanly@...rochip.com>, <linux-kernel@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <geert@...ux-m68k.org>,
        <linux-gpio@...r.kernel.org>, <linux-riscv@...ts.infradead.org>,
        <linux-crypto@...r.kernel.org>, <linux-usb@...r.kernel.org>,
        <bin.meng@...driver.com>, <linux-i2c@...r.kernel.org>,
        <alexandre.belloni@...tlin.com>, <Ivan.Griffin@...rochip.com>,
        <linux-rtc@...r.kernel.org>, <linux-spi@...r.kernel.org>,
        <a.zummo@...ertech.it>, <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 06/13] dt-bindings: rng: add bindings for microchip mpfs
 rng

On 10/11/2021 07:43, Krzysztof Kozlowski wrote:
> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> On 09/11/2021 14:36, Conor.Dooley@...rochip.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@...rochip.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@...rochip.com wrote:
>>>>>> From: Conor Dooley <conor.dooley@...rochip.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@...rochip.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@...rochip.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?
Correct, it needs one. Binding for that is here:
Documentation/devicetree/bindings/soc/microchip/microchip,polarfire-soc-sys-controller.yaml
> If it is a 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
>