Re: [PATCH 3/4] firmware: google: cbmem: Add to module device table

Re: [PATCH 3/4] firmware: google: cbmem: Add to module device table

[kernel test robot]

Hi Nícolas,

kernel test robot noticed the following build warnings:

[auto build test WARNING on next-20240111]
[also build test WARNING on v6.7]
[cannot apply to chrome-platform/for-next chrome-platform/for-firmware-next masahiroy-kbuild/for-next masahiroy-kbuild/fixes arm64/for-next/core linus/master v6.7 v6.7-rc8 v6.7-rc7]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/N-colas-F-R-A-Prado/firmware-coreboot-Generate-modalias-uevent-for-devices/20240111-231841
base:   next-20240111
patch link:    https://lore.kernel.org/r/20240111151226.842603-4-nfraprado%40collabora.com
patch subject: [PATCH 3/4] firmware: google: cbmem: Add to module device table
config: i386-randconfig-013-20240115 (https://download.01.org/0day-ci/archive/20240115/202401151013.Xioj5wZo-lkp@intel.com/config)
compiler: ClangBuiltLinux clang version 17.0.6 (https://github.com/llvm/llvm-project 6009708b4367171ccdbf4b5905cb6a803753fe18)
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240115/202401151013.Xioj5wZo-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202401151013.Xioj5wZo-lkp@intel.com/

All warnings (new ones prefixed by >>):

>> drivers/firmware/google/cbmem.c:118:40: warning: unused variable 'cbmem_ids' [-Wunused-const-variable]
     118 | static const struct coreboot_device_id cbmem_ids[] = {
         |                                        ^~~~~~~~~
   1 warning generated.


vim +/cbmem_ids +118 drivers/firmware/google/cbmem.c

   117	
 > 118	static const struct coreboot_device_id cbmem_ids[] = {
   119		{ .tag = LB_TAG_CBMEM_ENTRY },
   120		{ /* sentinel */ }
   121	};
   122	MODULE_DEVICE_TABLE(coreboot, cbmem_ids);
   123	

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Re: [PATCH 3/4] firmware: google: cbmem: Add to module device table

[Brian Norris]

Hi Nicolas,

On Mon, Jan 15, 2024 at 10:53:48AM +0800, kernel test robot wrote:
> All warnings (new ones prefixed by >>):
> 
> >> drivers/firmware/google/cbmem.c:118:40: warning: unused variable 'cbmem_ids' [-Wunused-const-variable]
>      118 | static const struct coreboot_device_id cbmem_ids[] = {
>          |                                        ^~~~~~~~~
>    1 warning generated.
> 
> 
> vim +/cbmem_ids +118 drivers/firmware/google/cbmem.c
> 
>    117	
>  > 118	static const struct coreboot_device_id cbmem_ids[] = {
>    119		{ .tag = LB_TAG_CBMEM_ENTRY },
>    120		{ /* sentinel */ }
>    121	};
>    122	MODULE_DEVICE_TABLE(coreboot, cbmem_ids);
>    123	

I was wondering why we have a seemingly unique "unused variable" failure
mode in comparison to other similarly-structured device/bus drivers, and
I realized that's because we're not relying on the same structure for
both MODULE_DEVICE_TABLE (struct coreboot_device_id) and for the driver
definition (struct coreboot_driver -> 'u32 tag'). Thus, this structure
is only used for #define MODULE builds, and otherwise not used.

Rather than wrapping these definitions in "#ifdef MODULE", perhaps we
can settle on a single field, and replace `struct coreboot_driver::tag`
with an instance of `struct coreboot_device_id`? That would normally be
a breaking change that would require changing all drivers at the same
time as the bus (or else some kind of intermediate transition state),
but considering there are only 4 driver implementations and they all
live under the same maintainer tree, that seems like it should still be
OK (IMO).

If it makes the series more readable/incremental, perhaps the switchover
can be the last patch in the series, and there can remain some
duplication (and potential -Wunused-const-variable issues) for the
middle of the series.

Brian