linux-kernel - Re: [PATCH] iio: bmi323: mark bmi323_ext_reg

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Message-ID: <a39002c0-923d-9c9d-6d42-ea6e4b9ec153@nfschina.com>
Date: Sat, 12 Oct 2024 18:21:46 +0800
From: Su Hui <suhui@...china.com>
To: Julia Lawall <julia.lawall@...ia.fr>
Cc: jagathjog1996@...il.com, jic23@...nel.org, lars@...afoo.de,
 nathan@...nel.org, ndesaulniers@...gle.com, morbo@...gle.com,
 justinstitt@...gle.com, benato.denis96@...il.com,
 Jonathan.Cameron@...wei.com, linux-iio@...r.kernel.org,
 linux-kernel@...r.kernel.org, llvm@...ts.linux.dev,
 kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] iio: bmi323: mark bmi323_ext_reg_savestate as maybe
 unused

On 2024/10/12 17:11, Julia Lawall wrote:
> On Sat, 12 Oct 2024, Su Hui wrote:
>
>> When running 'make CC=clang drivers/iio/imu/bmi323/bmi323_core.o', there
>> is a clang warning as follows:
>>
>> drivers/iio/imu/bmi323/bmi323_core.c:133:27: error:
>> variable 'bmi323_ext_reg_savestate' is not needed and will not be emitted
>> [-Werror,-Wunneeded-internal-declaration]
>>    133 | static const unsigned int bmi323_ext_reg_savestate[] = {
>>        |                           ^~~~~~~~~~~~~~~~~~~~~~~~
>> 1 error generated.
>>
>> Mark bmi323_ext_reg_savestate as __maybe_unused to silent this warning.
> Why might it be unused?

We only use the size of 'bmi323_ext_reg_savestate[]' not it's value, as 
shown below :

$ git grep  bmi323_ext_reg_savest drivers/iio/imu/
drivers/iio/imu/bmi323/bmi323_core.c:static const unsigned int 
bmi323_ext_reg_savestate[] = {
drivers/iio/imu/bmi323/bmi323_core.c:   unsigned int 
ext_reg_settings[ARRAY_SIZE(bmi323_ext_reg_savestate)];
drivers/iio/imu/bmi323/bmi323_core.c:   for (unsigned int i = 0; i < 
ARRAY_SIZE(bmi323_ext_reg_savestate); i++) {
drivers/iio/imu/bmi323/bmi323_core.c:   for (unsigned int i = 0; i < 
ARRAY_SIZE(bmi323_ext_reg_savestate); i++) {

And I find some solutions use __maybe_unused to silent this warning. 
Like this one:
3034983db355 ("drm/amdgpu: Mark mmhub_v1_8_mmea_err_status_reg as 
__maybe_unused")

Mark this variable to __maybe_unused is  to eliminate clang's warning.
Perhaps it is also possible to mark it as _used:).

Su Hui