linux-kernel - Re: [PATCH 1/2] dt-bindings: reset: Updated binding for Versal-NET reset driver

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Message-ID: <4c932cbf-19db-2c88-2558-aa42c5338598@linaro.org>
Date:   Tue, 18 Jul 2023 16:04:49 +0200
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Michal Simek <michal.simek@....com>,
        Conor Dooley <conor@...nel.org>,
        Piyush Mehta <piyush.mehta@....com>
Cc:     robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        conor+dt@...nel.org, p.zabel@...gutronix.de,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        git@....com
Subject: Re: [PATCH 1/2] dt-bindings: reset: Updated binding for Versal-NET
 reset driver

On 18/07/2023 16:01, Michal Simek wrote:
> 
> 
> On 7/18/23 15:20, Krzysztof Kozlowski wrote:
>> On 18/07/2023 15:11, Michal Simek wrote:
>>>>>
>>>>> That numbers in DT are virtual no matter if you use ID from 0 to max or random
>>>>> values it is up to code to handle them. Checking nr_pins against ID is done in
>>>>> core but it is up to drivers.
>>>>
>>>> No, you confuse "virtual" and "ID". IDs are not virtual. IDs are real
>>>> and have representation in Linux driver. You do not need to define
>>>> anything virtual in the bindings.
>>>
>>> Not sure how you define ID itself. But HW doesn't know ID. HW knows only
>>> register which you can use to perform the reset. It is not really 128bit
>>> register where every bit targets to different IP.
>>>
>>> And this is SW-firmware interface like SCMI reset driver.
>>>
>>> Firmware is saying that ID 0 is QSPI, ID 1 is MMC.
>>> Their Linux driver is asking for nr_reset via firmware call which can be
>>> different for different SOC and that's fine and I have no problem with it.
>>> But only SCMI server is dictating that ID 0 is QSPI and ID 1 is MMC. Different
>>> SCMI server implementation can map it differently.
>>
>> Sure, and all this points to: no need for bindings.
>>
>>>
>>>
>>>>> In our case that IDs are coming from firmware and driver itself is just matching
>>>>> them.
>>>>
>>>> So they are the same as if coming from hardware - no need for IDs.
>>>
>>> It is hard to say what hardware here exactly is. From my perspective and I am
>>> not advocating not using IDs from 0 to max, it is just a number.
>>>
>>> If my firmware knows that QSPI reset is 0xc10402dU then I will just pass it to
>>> reach my goal which is reset QSPI IP.
>>>
>>> If you think that we should use IDs from 0 to max NR I am happy to pass this
>>> message to PM team and we should extend any SW to do translation between.
>>
>> When we talk about IDs and bindings, we mean IDs meaningful to Linux.
>> Whatever is ignored by Linux and passed to anyone else - hardware or
>> firmware - is not a ID anymore from bindings point of view. It's just
>> some value.
> 
> Please correct me if I am wrong. Description about ID should be removed from 
> commit message because it is not necessary. And
> include/dt-bindings/reset/xlnx-versal-net-resets.h
> should be added when we merge also DT for versal-net SOC.

No, the binding header is needed only if driver is using it. Adding DTS
will not change that - still no kernel driver users. No benefits of such
binding. If there are no users and no benefits - don't make it a binding.

Best regards,
Krzysztof