linux-kernel - Re: [PATCH v3 05/10] dt-bindings: timer: Add HPE GXP Timer Binding

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Date:   Fri, 11 Mar 2022 18:13:51 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...onical.com>
To:     "Hawkins, Nick" <nick.hawkins@....com>,
        Rob Herring <robh@...nel.org>
Cc:     "Verdun, Jean-Marie" <verdun@....com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 05/10] dt-bindings: timer: Add HPE GXP Timer Binding

On 11/03/2022 17:22, Hawkins, Nick wrote:
> On Thu, Mar 10, 2022 at 01:52:24PM -0600, nick.hawkins@....com wrote:
>>> From: Nick Hawkins <nick.hawkins@....com>>
>>>
>>> Creating binding for gxp timer in device tree hpe,gxp-timer Although 
>>> there are multiple times on the SoC we are only enabling one at this 
>>> time.
>>>
>>> Signed-off-by: Nick Hawkins <nick.hawkins@....com>>
>>>
>>> ----
>>>
>>> v2:
>>>  *Removed maintainer change from patch  *Verified there was no 
>>> compilation errors  *Added reference code in separate patch of 
>>> patchset
>>> ---
>>>  .../bindings/timer/hpe,gxp-timer.yaml         | 45 +++++++++++++++++++
>>>  1 file changed, 45 insertions(+)
>>>  create mode 100644 
>>> Documentation/devicetree/bindings/timer/hpe,gxp-timer.yaml
>>>
>>> diff --git 
>>> a/Documentation/devicetree/bindings/timer/hpe,gxp-timer.yaml 
>>> b/Documentation/devicetree/bindings/timer/hpe,gxp-timer.yaml
>>> new file mode 100644
>>> index 000000000000..1f4e345c5fb8
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/timer/hpe,gxp-timer.yaml
>>> @@ -0,0 +1,45 @@
>>> +# SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) %YAML 1.2
>>> +---
>>> +$id: 
>>> +INVALID URI REMOVED
>>> +xp-timer.yaml*__;Iw!!NpxR!yaItMPvjqEf3fKyp1xDQAzawRQDd8uDGTNKMlVPpn5Y
>>> +56IUABMYbali7jonBl20K$
>>> +$schema: 
>>> +INVALID URI REMOVED
>>> +aml*__;Iw!!NpxR!yaItMPvjqEf3fKyp1xDQAzawRQDd8uDGTNKMlVPpn5Y56IUABMYba
>>> +li7jmX565-G$
>>> +
>>> +title: HPE GXP TIMER
>>> +
>>> +maintainers:
>>> +  - Nick Hawkins <nick.hawkins@....com>>
>>> +  - Jean-Marie Verdun <verdun@....com>>
>>> +
>>> +properties:
>>> +  compatible:
>>> +    const: hpe,gxp-timer
>>> +
>>> +  reg:
>>> +    items:
>>> +      - description: T0CNT register
>>> +      - description: T0CS register
>>> +      - description: TIMELO register
> 
>> Is the spec public to know what T0CNT, T0CS, and TIMELO are?
> No it is not, should I not mention the register descriptions at all?
> 
>>> +
>>> +  interrupts:
>>> +    maxItems: 1
>>> +
>>> +  clock-frequency:
>>> +    description: The frequency of the clock that drives the counter, in Hz.
>>> +
>>> +required:
>>> +  - compatible
>>> +  - reg
>>> +  - interrupts
>>> +  - clock-frequency
>>> +
>>> +additionalProperties: false
>>> +
>>> +examples:
>>> +  - |
>>> +    timer@...03000 {
>>> +        compatible = "hpe,gxp-timer";
>>> +        reg = <0xc0000080 0x1>>, <0xc0000094 0x01>>, <0xc0000088 0x08>>;
> 
>> Based on the driver these are 4 bytes, 1 byte, 4 bytes in size.
> 
>> Are there other registers in 0x80-0x95 range or do these offsets change in other chips? If not, just 1 entry covering the whole thing would be better.
> There are other registers in this range that cover different timers/clocks, for the most part between chip generations the offsets remain the same unless there is an architectural issue.
> Can you provide a quick example of what one entry would be?

arch/arm/boot/dts/versatile-ab.dts

and actually 90% of DTS... it's rather a challange to find such
fine-grained iomap.

Best regards,
Krzysztof