drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

[kernel test robot]

Hi Javier,

FYI, the error/warning still remains.

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@intel.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[] = {
   155		{ "sh1106",  SH1106_ID },
   156		{ "ssd1305", SSD1305_ID },
   157		{ "ssd1306", SSD1306_ID },
   158		{ "ssd1307", SSD1307_ID },
   159		{ "ssd1309", SSD1309_ID },
   160		{ /* sentinel */ }
   161	};
   162	MODULE_DEVICE_TABLE(spi, ssd130x_spi_table);
   163	

-- 
0-DAY CI Kernel Test Service
https://01.org/lkp

Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

[Javier Martinez Canillas]

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@intel.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

Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

[Nathan Chancellor]

On Sat, May 28, 2022 at 11:23:04PM +0200, Javier Martinez Canillas wrote:
> 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.

I don't think it is a false positive for this particular configuration.
MODULE_DEVICE_TABLE expands to nothing when the file it is included in
is built into the kernel, as opposed to a module, so the variable truly
is unused.

$ curl -LSs https://download.01.org/0day-ci/archive/20220529/202205290422.eoxGqDMR-lkp@intel.com/config | rg CONFIG_DRM_SSD130X_SPI
CONFIG_DRM_SSD130X_SPI=y

You'll see the same warning with GCC and a similar configuration:

drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: error: ‘ssd130x_spi_table’ defined but not used [-Werror=unused-const-variable=]
  154 | static const struct spi_device_id ssd130x_spi_table[] = {
      |                                   ^~~~~~~~~~~~~~~~~
cc1: all warnings being treated as errors

At the end of the day, this warning only shows up under W=1, so take it
as you will. The kernel test robot is a sign, not a cop :)

Cheers,
Nathan

> > 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@intel.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
> 
> 

Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

[Javier Martinez Canillas]

Hello Nathan,

On 5/29/22 03:01, Nathan Chancellor wrote:
> On Sat, May 28, 2022 at 11:23:04PM +0200, Javier Martinez Canillas wrote:
>> 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.
> 
> I don't think it is a false positive for this particular configuration.
> MODULE_DEVICE_TABLE expands to nothing when the file it is included in
> is built into the kernel, as opposed to a module, so the variable truly
> is unused.
>

I know that is not used but my point is that we shouldn't need that table
in the first place. The only reason we add it is to workaround a bug in
the SPI core.
 
> $ curl -LSs https://download.01.org/0day-ci/archive/20220529/202205290422.eoxGqDMR-lkp@intel.com/config | rg CONFIG_DRM_SSD130X_SPI
> CONFIG_DRM_SSD130X_SPI=y
> 
> You'll see the same warning with GCC and a similar configuration:
>

Yes, I'm not saying that the compiler warning is a false positive but
that the reported error for this driver is. Since the correct fix on
a driver that support SPI platform devices would be to use the table
and set it to the struct spi_driver .id field.
 
> drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: error: ‘ssd130x_spi_table’ defined but not used [-Werror=unused-const-variable=]
>   154 | static const struct spi_device_id ssd130x_spi_table[] = {
>       |                                   ^~~~~~~~~~~~~~~~~
> cc1: all warnings being treated as errors
> 
> At the end of the day, this warning only shows up under W=1, so take it
> as you will. The kernel test robot is a sign, not a cop :)
>

I guess something that could be done is to guard the definition of the
ssd130x_spi_table with a `if IS_MODULE(CONFIG_DRM_SSD130X_SPI)`, since
if the symbol is 'y' and the driver built-in, then won't be used indeed.
 
> Cheers,
> Nathan
> 
-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat

Re: drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: warning: unused variable 'ssd130x_spi_table'

[Javier Martinez Canillas]

On 5/29/22 09:34, Javier Martinez Canillas wrote:
> Hello Nathan,

[snip]

>>
>> You'll see the same warning with GCC and a similar configuration:
>>
> 
> Yes, I'm not saying that the compiler warning is a false positive but
> that the reported error for this driver is. Since the correct fix on
> a driver that support SPI platform devices would be to use the table
> and set it to the struct spi_driver .id field.
>  
>> drivers/gpu/drm/solomon/ssd130x-spi.c:154:35: error: ‘ssd130x_spi_table’ defined but not used [-Werror=unused-const-variable=]
>>   154 | static const struct spi_device_id ssd130x_spi_table[] = {
>>       |                                   ^~~~~~~~~~~~~~~~~
>> cc1: all warnings being treated as errors
>>
>> At the end of the day, this warning only shows up under W=1, so take it
>> as you will. The kernel test robot is a sign, not a cop :)
>>
> 
> I guess something that could be done is to guard the definition of the
> ssd130x_spi_table with a `if IS_MODULE(CONFIG_DRM_SSD130X_SPI)`, since
> if the symbol is 'y' and the driver built-in, then won't be used indeed.
>  

I posted https://lists.freedesktop.org/archives/dri-devel/2022-May/357088.html
to fix this compile warning. Thanks folks!

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat