s390 does not provide ioremap()/iounmap() when CONFIG_HAS_IOMEM is not
set (which requires CONFIG_PCI on that architecture). This causes a
build failure with Rust enabled on e.g. s390 allnoconfig:
In file included from rust/helpers/helpers.c:68:
rust/helpers/io.c:8:9: error: call to undeclared function 'ioremap'; ISO C99 and later do not support implicit function declarations
[-Wimplicit-function-declaration]
8 | return ioremap(offset, size);
| ^
rust/helpers/io.c:19:2: error: call to undeclared function 'iounmap'; ISO C99 and later do not support implicit function declarations
[-Wimplicit-function-declaration]
19 | iounmap(addr);
Guard the C helpers behind #ifdef CONFIG_HAS_IOMEM and cfg-gate the Rust
io::mem module, such that IoMem, ExclusiveIoMem and IoRequest are not
available without CONFIG_HAS_IOMEM.
Note that the C API is inconsistent about this. For instance,
devm_ioremap() has no stub and produces a link failure without
CONFIG_HAS_IOMEM, whereas devm_platform_ioremap_resource() provides an
inline stub returning -EINVAL.
The approach taken here (compile-time gating) matches the former, which
is slightly more appropriate since any driver performing MMIO currently
requires CONFIG_HAS_IOMEM.
Ideally, s390 should provide ioremap()/iounmap() stubs unconditionally
(as UML already does), removing the need for any config gating as
discussed in [1]; a follow-up patch for s390 is expected.
Cc: Arnd Bergmann <arnd@arndb.de>
Reported-by: Miguel Ojeda <ojeda@kernel.org>
Closes: https://lore.kernel.org/all/20260803180931.97202-1-ojeda@kernel.org [1]
Fixes: 3f70ebe638 ("s390: Enable Rust support")
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Link: https://patch.msgid.link/20260805212920.1996937-1-dakr@kernel.org
Signed-off-by: Danilo Krummrich <dakr@kernel.org>
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