linux-kernel - Re: [PATCH 4/4] iio: proximity: sx9500: Mark ACPI and OF related data as maybe unused

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Date:   Sun, 12 Mar 2023 11:17:05 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Jonathan Cameron <jic23@...nel.org>
Cc:     Marek Vasut <marek.vasut@...il.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Michael Hennerich <Michael.Hennerich@...log.com>,
        Robert Eshleman <bobbyeshleman@...il.com>,
        linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] iio: proximity: sx9500: Mark ACPI and OF related data
 as maybe unused

On 11/03/2023 19:44, Jonathan Cameron wrote:
> On Sat, 11 Mar 2023 13:30:01 +0100
> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
> 
>> On 11/03/2023 13:28, Jonathan Cameron wrote:
>>> On Sat, 11 Mar 2023 12:14:57 +0100
>>> Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org> wrote:
>>>   
>>>> The driver can be compile tested with !CONFIG_OF or !CONFIG_ACPI making
>>>> certain data unused:
>>>>
>>>>   drivers/iio/proximity/sx9500.c:1039:34: error: ‘sx9500_of_match’ defined but not used [-Werror=unused-const-variable=]
>>>>
>>>> Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>  
>>>
>>> Hi Krysztof
>>>
>>> Thanks for looking at these warnings. 
>>>
>>> Drop the protection macros instead.  The tables are trivial in size and
>>> the of_match_ptr() breaks some ways this driver can be used.
>>> ACPI_PTR() isn't as bad, but is pretty much pointless given this size of
>>> the array. 
>>>   
>>
>> For ACPI platform, ACPI table is used, so nothing for PRP0001. For OF
>> platform, OF table is used.
> 
> So you would think, but nope.. That's not how it works (I was surprised
> when I came across this the first time too)
>  
> PRP0001 is magic and requires no specific support in an individual
> driver beyond not using that of_match_ptr() macro!

I know, we talk about ACPI table.

> 
> https://elixir.bootlin.com/linux/latest/source/drivers/acpi/bus.c#L754
> Docs here
> https://elixir.bootlin.com/linux/latest/source/Documentation/firmware-guide/acpi/enumeration.rst#L450

The code is compile when CONFIG_ACPI is defined, right? Then you have
ACPI table, so what for ACPI platform is missing? ACPI platform has ACPI
table.

Best regards,
Krzysztof