linux-kernel - Re: [PATCH 1/2] dt-bindings: timer: add a binding for LiteX Timer

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Date:   Tue, 22 Nov 2022 08:53:15 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Icenowy Zheng <uwu@...nowy.me>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Karol Gugala <kgugala@...micro.com>,
        Mateusz Holenko <mholenko@...micro.com>,
        Gabriel Somlo <gsomlo@...il.com>, Joel Stanley <joel@....id.au>
Cc:     linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH 1/2] dt-bindings: timer: add a binding for LiteX Timer

On 21/11/2022 15:39, Icenowy Zheng wrote:
> 在 2022-11-21星期一的 11:19 +0100，Krzysztof Kozlowski写道：
>> On 21/11/2022 05:25, Icenowy Zheng wrote:
>>> The LiteX SoC generator has a timer core, which by default only
>>> generates a simple down counter.
>>
>> Subject: drop second, redundant "bindings".
>>
>>>
>>> Add a DT binding for it.
>>>
>>> Signed-off-by: Icenowy Zheng <uwu@...nowy.me>
>>> ---
>>>  .../bindings/timer/litex,timer.yaml           | 52
>>> +++++++++++++++++++
>>>  1 file changed, 52 insertions(+)
>>>  create mode 100644
>>> Documentation/devicetree/bindings/timer/litex,timer.yaml
>>>
>>> diff --git
>>> a/Documentation/devicetree/bindings/timer/litex,timer.yaml
>>> b/Documentation/devicetree/bindings/timer/litex,timer.yaml
>>> new file mode 100644
>>> index 000000000000..bece07586c6b
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/timer/litex,timer.yaml
>>> @@ -0,0 +1,52 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause)
>>> +%YAML 1.2
>>> +---
>>> +$id: http://devicetree.org/schemas/timer/litex,timer.yaml#
>>> +$schema: http://devicetree.org/meta-schemas/core.yaml#
>>> +
>>> +title: LiteX Timer
>>> +
>>> +maintainers:
>>> +  - Icenowy Zheng <uwu@...nowy.me>
>>> +
>>> +description: |
>>> +  The LiteX Timer is a count-down timer that is defaultly embedded
>>> +  into all LiteX SoCs, unless explicitly disabled. It's fed
>>> directly
>>> +  by the system clock like other LiteX peripherals.
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: litex,timer
>>
>> No model name/number? If it is part of Soc, then a SoC specific
>> number
>> is expected usually.
> 
> Ah it's part of a SoC generator, as a default core. [1]
> 
> If you like, I think the version of LiteX SoC generator itself could be
> added, like `litex,timer-22.08`.

How can you be sure that all soft-cores from Litex will be exactly the
same and use the same compatible? The naming is poor here, but I don't
know whether some arbitrary version number is the solution.

> 
>>
>>> +
>>> +  reg:
>>> +    maxItems: 1
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clocks:
>>> +    maxItems: 1
>>> +
>>> +  litex,width:
>>> +    description:
>>> +      The width of the timer's value, specified as the width
>>> argument
>>> +      when creating an instance of litex.soc.cores.Timer.
>>
>> This lacks type ($ref) and units in description, but more important -
>> why this is not part of compatible? Is it a width of register(s)?
>>
>> And what is "instance of litex.soc.cores.Timer"? Is it configurable,
>> soft-core?
> 
> Yes, it is a configurable soft core, although the configuration of a
> non-32-bit counter is only available when directly generating this core
> w/o using the full SoC generator (the full SoC generator defaults to
> 32-bit).
> 
>>
>> BTW, there is reg-io-width property.
> 
> This is not register I/O width, it's only the width of the counter.
> 
> And because of the LiteX CSR bus nature, all registers after this will
> be automatically moved if this register's size goes beyond the
> alignment (current all LiteX support in Linux mainline assumes 32-bit
> alignment, which is also the default configuration).

OK

Best regards,
Krzysztof