linux-kernel - Re: [RFC PATCH 3/7] dt-bindings: bus: add STM32MP15 ETZPC firewall bus bindings

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Message-ID: <19157c67-fa83-e598-d7ee-c313f3d4b198@foss.st.com>
Date:   Mon, 9 Jan 2023 12:54:08 +0100
From:   Gatien CHEVALLIER <gatien.chevallier@...s.st.com>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        <alexandre.torgue@...s.st.com>, <robh+dt@...nel.org>,
        <Oleksii_Moisieiev@...m.com>, <linus.walleij@...aro.org>,
        <gregkh@...uxfoundation.org>
CC:     <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <loic.pallardy@...com>,
        <devicetree@...r.kernel.org>, <mark.rutland@....com>,
        <arnd@...db.de>
Subject: Re: [RFC PATCH 3/7] dt-bindings: bus: add STM32MP15 ETZPC firewall
 bus bindings



On 1/5/23 22:53, Krzysztof Kozlowski wrote:
> On 04/01/2023 14:43, Gatien CHEVALLIER wrote:
>> Hello Krzysztof,
>>
>> On 12/22/22 14:57, Krzysztof Kozlowski wrote:
>>> On 22/12/2022 14:51, Gatien CHEVALLIER wrote:
>>>> Hello,
>>>>
>>>> On 12/22/22 11:26, Krzysztof Kozlowski wrote:
>>>>> On 21/12/2022 18:30, Gatien Chevallier wrote:
>>>>>> Adds the list of peripherals IDs under firewall bus on STM32MP15.
>>>>>>
>>>>>> Signed-off-by: Gatien Chevallier <gatien.chevallier@...s.st.com>
>>>>>> ---
>>>>>>     include/dt-bindings/bus/stm32mp15_sys_bus.h | 98 +++++++++++++++++++++
>>>>>>     1 file changed, 98 insertions(+)
>>>>>>     create mode 100644 include/dt-bindings/bus/stm32mp15_sys_bus.h
>>>>>>
>>>>>> diff --git a/include/dt-bindings/bus/stm32mp15_sys_bus.h b/include/dt-bindings/bus/stm32mp15_sys_bus.h
>>>>>> new file mode 100644
>>>>>> index 000000000000..97eacc7b5f16
>>>>>> --- /dev/null
>>>>>> +++ b/include/dt-bindings/bus/stm32mp15_sys_bus.h
>>>>>
>>>>> That's wrong in multiple ways:
>>>>> 1. No underscores
>>>>> 2. Missing vendor prefix
>>>>> 3. Name not matching compatible.
>>>>
>>>> Sure, will comply in V3.
>>>>
>>>>>
>>>>>> @@ -0,0 +1,98 @@
>>>>>> +/* SPDX-License-Identifier: (GPL-2.0-only OR BSD-2-Clause) */
>>>>>> +/*
>>>>>> + * Copyright (C) STMicroelectronics 2022 - All Rights Reserved
>>>>>> + */
>>>>>> +#ifndef _DT_BINDINGS_BUS_STM32MP15_SYS_BUS_H
>>>>>> +#define _DT_BINDINGS_BUS_STM32MP15_SYS_BUS_H
>>>>>> +
>>>>>> +/* ETZPC IDs */
>>>>>> +#define STM32MP1_ETZPC_STGENC_ID	0
>>>>>> +#define STM32MP1_ETZPC_BKPSRAM_ID	1
>>>>>> +#define STM32MP1_ETZPC_IWDG1_ID		2
>>>>>> +#define STM32MP1_ETZPC_USART1_ID	3
>>>>>> +#define STM32MP1_ETZPC_SPI6_ID		4
>>>>>> +#define STM32MP1_ETZPC_I2C4_ID		5
>>>>>> +/* ID 6 reserved */
>>>>>
>>>>> Reserved why? These are IDs so they start from 0 and go by 0. Don't
>>>>> hard-code some register offsets.
>>>>
>>>> Here, I do define IDs. Some appear as reserved based on what I've seen
>>>> in the SoC datasheet that states these as "indexes"
>>>>
>>>> Please see the table 94 in chapter 15.6 (ETZPC) of the STM32MP157
>>>> Reference manual:
>>>> [1] https://www.st.com/resource/en/reference_manual/DM00327659-.pdf
>>>
>>> Then why do you define them in bindings? Use raw numbers. Do you see
>>> anywhere in arm/arm64 bindings for GIC_SPI interrupt numbers?
>>>
>>
>> What would you think of simply removing the comments that state that IDs
>> are reserved, mimicking the way it is for qcom bindings? Fundamentally,
>> they are indeed only IDs and could be raw numbers.
> 
> If these are IDs then there are no reserved numbers and they are
> continuous from 0 to X. Without gaps.
> 
>> IMO, this makes reading the device tree harder. Because you'd have to
>> look what the raw number corresponds to.
> 
> Sure, but that's not the reason to put numbers to the bindings... You
> mix defines with bindings.
> 
>> To take an example, it has already been done for SCMI clocks and I find
>> it eases comprehension.
> 
> You need to be a bit more specific...

Please see include/dt-bindings/clock/stm32mp1-clks.h, where there are 
various clock IDs defined, some of them not contiguous.

Errata: for SCMI clocks they are indeed contiguous but not clock IDs.

> 
> Anyway, IDs should be placed in bindings. Some mapping of
> internal/hardware ports, registers, offsets, values - usually not.
> 
> I don't know where exactly your case fits, but when some IDs are
> reserved it is a clear sign that these are not IDs (again - IDs start
> from 0 and go incrementally by one, without gaps).
> 

I do agree with your statement that IDs should not be reserved.

I think I've missed something to better highlight my point of view: It 
would be perfectly fine using numbers that are not described in this 
bindings file. It would just not correspond to an ID of a peripheral 
described in the SoC reference manual, thus making no sense to use them. 
Stating that they are reserved was incorrect, it's just that peripherals 
get a firewall ID, depending on the platform.

I think it should be okay not describing IDs that are not relevant, what 
do you think? I found that in include/dt-bindings/arm/qcom,ids.h, IDs 
are not continuous. Not mentioning an ID could be used for deprecation.

> 
> Best regards,
> Krzysztof
> 

Best regards,
Gatien