linux-kernel - Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi

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Date:   Sat, 28 May 2022 23:23:04 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     kernel test robot <lkp@...el.com>
Cc:     llvm@...ts.linux.dev, kbuild-all@...ts.01.org,
        linux-kernel@...r.kernel.org,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused
 variable 'ssd130x_spi_table'

Hello,

On 5/28/22 22:58, kernel test robot wrote:
> Hi Javier,
> 
> FYI, the error/warning still remains.
>

Yes, but in my opinion is a false positive.
 
> tree:   https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git master
> head:   9d004b2f4fea97cde123e7f1939b80e77bf2e695
> commit: 74373977d2ca26e5735377f8874be70bc2f030f5 drm/solomon: Add SSD130x OLED displays SPI support
> date:   5 weeks ago
> config: hexagon-randconfig-r033-20220529 (https://download.01.org/0day-ci/archive/20220529/202205290422.eoxGqDMR-lkp@intel.com/config)
> compiler: clang version 15.0.0 (https://github.com/llvm/llvm-project 0fbe3f3f486e01448121f7931a4ca29fac1504ab)
> reproduce (this is a W=1 build):
>         wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
>         chmod +x ~/bin/make.cross
>         # https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=74373977d2ca26e5735377f8874be70bc2f030f5
>         git remote add linus https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
>         git fetch --no-tags linus master
>         git checkout 74373977d2ca26e5735377f8874be70bc2f030f5
>         # save the config file
>         mkdir build_dir && cp config build_dir/.config
>         COMPILER_INSTALL_PATH=$HOME/0day COMPILER=clang make.cross W=1 O=build_dir ARCH=hexagon SHELL=/bin/bash drivers/gpu/drm/solomon/
> 
> If you fix the issue, kindly add following tag where applicable
> Reported-by: kernel test robot <lkp@...el.com>
> 
> All warnings (new ones prefixed by >>):
> 
>>> drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table' [-Wunused-const-variable]
>    static const struct spi_device_id ssd130x_spi_table[] = {
>                                      ^
>    1 warning generated.
> 
> 
> vim +/ssd130x_spi_table +154 drivers/gpu/drm/solomon/ssd130x-spi.c
> 
>    145	
>    146	/*
>    147	 * The SPI core always reports a MODALIAS uevent of the form "spi:<dev>", even
>    148	 * if the device was registered via OF. This means that the module will not be
>    149	 * auto loaded, unless it contains an alias that matches the MODALIAS reported.
>    150	 *
>    151	 * To workaround this issue, add a SPI device ID table. Even when this should
>    152	 * not be needed for this driver to match the registered SPI devices.
>    153	 */
>  > 154	static const struct spi_device_id ssd130x_spi_table[] = {

This comment is quite clear about it, the table only exists due a limitation in how
the SPI subsystem reports the module aliases. It always report a "spi:<device> even
if it was registered by OF, and that's the only reason why we need it.

Setting the struct spi_driver .id field just to make this warning go away would be
the wrong thing to do IMO, since always the struct of_device_id should be used.

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat