Re: [PATCH] powerpc: iommu: fix build when neither PCI or IBMVIO is set

Randy Dunlap [off-list ref] writes:

When neither CONFIG_PCI nor CONFIG_IBMVIO is enabled:

../arch/powerpc/kernel/iommu.c:178:30: error: 'fail_iommu_bus_notifier' defined but not used [-Werror=unused-variable]
  178 | static struct notifier_block fail_iommu_bus_notifier = {

If only that struct is bounded by 2 #if defined() phrases (PCI && IBMVIO):

../arch/powerpc/kernel/iommu.c:162:12: error: 'fail_iommu_bus_notify' defined but not used [-Werror=unused-function]
  162 | static int fail_iommu_bus_notify(struct notifier_block *nb,

If that function is also guarded by 2 #if defined() phrases:

In file included from ../include/linux/dma-mapping.h:7,
                 from ../arch/powerpc/kernel/iommu.c:19:
../include/linux/device.h:131:26: error: 'dev_attr_fail_iommu' defined but not used [-Werror=unused-variable]
  131 |  struct device_attribute dev_attr_##_name = __ATTR_RW(_name)
../arch/powerpc/kernel/iommu.c:160:8: note: in expansion of macro 'DEVICE_ATTR_RW'
  160 | static DEVICE_ATTR_RW(fail_iommu);

and the snowball continues to grow.
Next I got this one:

../arch/powerpc/kernel/iommu.c: In function 'iommu_range_alloc':
../arch/powerpc/kernel/iommu.c:234:6: error: implicit declaration of function 'should_fail_iommu'; did you mean 'should_failslab'? [-Werror=implicit-function-declaration]
  234 |  if (should_fail_iommu(dev))

and

../arch/powerpc/kernel/iommu.c: In function 'should_fail_iommu':
../arch/powerpc/kernel/iommu.c:122:50: error: 'fail_iommu' undeclared (first use in this function)
  122 |  return dev->archdata.fail_iommu && should_fail(&fail_iommu, 1);

So combine CONFIG_FAIL_IOMMU && (CONFIG_PCI || CONFIG_IBMVIO)
to decide on building some of this code/data.

Couldn't we just make FAIL_IOMMU depend on PCI || IBMVIO?

cheers