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

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Message-ID: <20230311184440.22a1ff0f@jic23-huawei>
Date:   Sat, 11 Mar 2023 18:44:40 +0000
From:   Jonathan Cameron <jic23@...nel.org>
To:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.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 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!

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
> 
> What usage exactly is broken here? What ways?
> 
> Best regards,
> Krzysztof
>