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

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Message-ID: <5c45d89b-00c5-a330-2e1f-b99043736527@linaro.org>
Date:   Tue, 18 Jul 2023 15:21:33 +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 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.

And just some proofs:
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/include/dt-bindings/reset/xlnx-versal-resets.h?h=v6.5-rc2
$ git grep VERSAL_RST
Results: No users.

Best regards,
Krzysztof