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

From: Krzysztof Kozlowski <krzk@kernel.org>
To: Gatien CHEVALLIER <gatien.chevallier@foss.st.com>,
	alexandre.torgue@foss.st.com, robh+dt@kernel.org,
	Oleksii_Moisieiev@epam.com, linus.walleij@linaro.org,
	gregkh@linuxfoundation.org
Cc: linux-stm32@st-md-mailman.stormreply.com,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, loic.pallardy@st.com,
	devicetree@vger.kernel.org, mark.rutland@arm.com, arnd@arndb.de
Subject: Re: [RFC PATCH 3/7] dt-bindings: bus: add STM32MP15 ETZPC firewall bus bindings
Date: Thu, 5 Jan 2023 22:53:58 +0100	[thread overview]
Message-ID: <dfe328fc-349b-3357-a8ac-6fc363f403fc@kernel.org> (raw)
In-Reply-To: <8f022dc8-d728-ba91-35ed-8a4006855f0d@foss.st.com>

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@foss.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...

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).

Best regards,
Krzysztof

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