arm64/io: add constant-argument check

From: Arnd Bergmann <[email protected]>

In some configurations __const_iowrite32_copy() does not get inlined and gcc runs into the BUILD_BUG():

In file included from <command-line>:
In function '__const_memcpy_toio_aligned32',

    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:203:3,
    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:199:20:

include/linux/compiler_types.h:487:45: error: call to '__compiletime_assert_538' declared with attribute error: BUILD_BUG failed
487 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^
include/linux/compiler_types.h:468:25: note: in definition of macro '__compiletime_assert'

  468 |                         prefix ## suffix();                             \
      |                         ^~~~~~
include/linux/compiler_types.h:487:9: note: in expansion of macro '_compiletime_assert'
  487 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
   59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
      |                     ^~~~~~~~~~~~~~~~
arch/arm64/include/asm/io.h:193:17: note: in expansion of macro 'BUILD_BUG'
  193 |                 BUILD_BUG();
      |                 ^~~~~~~~~

Move the check for constant arguments into the inline function to ensure it is still constant if the compiler decides against inlining it, and mark them as __always_inline to override the logic that sometimes leads to the compiler not producing the simplified output.

Note that either the __always_inline annotation or the check for a constant value are sufficient here, but combining the two looks cleaner as it also avoids the macro. With clang-8 and older, the macro was still needed, but all versions of gcc and clang can reliably perform constant folding here.

Fixes ead79118dae6 ("arm64/io: Provide a WC friendly __iowriteXX_copy()")

Signed-off-by Arnd Bergmann <[email protected]>

+#define __iowrite64_copy(to, from, count) __iowrite64_copy(to, from, count)

Quoted 5 lines · Arnd Bergmann

Move the check for constant arguments into the inline function to ensure it is still constant if the compiler decides against inlining it, and mark them as __always_inline to override the logic that sometimes leads to the compiler not producing the simplified output.

Quoted 8 lines

Note that either the __always_inline annotation or the check for a constant value are sufficient here, but combining the two looks cleaner as it also avoids the macro. With clang-8 and older, the macro was still needed, but all versions of gcc and clang can reliably perform constant folding here.

Fixes ead79118dae6 ("arm64/io: Provide a WC friendly __iowriteXX_copy()")

Signed-off-by Arnd Bergmann <[email protected]>

I have a trivial nit below, but either way this looks good to me, so regardless of that:

Reviewed-by Mark Rutland <[email protected]>

arch/arm64/include/asm/io.h static inline void __const_memcpy_toio_aligned32(volatile u32 __iomem *to, · line 211

Quoted 13 lines

arch/arm64/include/asm/io.h +5 -1

+static __always_inline void
+__iowrite32_copy(void __iomem *to, const void *from, size_t count)
 {
-	if (count == 8 || count == 4 || count == 2 || count == 1) {
+	if (__builtin_constant_p(count) &&
+	    (count == 8 || count == 4 || count == 2 || count == 1)) {
 		__const_memcpy_toio_aligned32(to, from, count);
 		dgh();
 	} else {
 		__iowrite32_copy_full(to, from, count);
 	}
 }
+#define __iowrite32_copy(to, from, count) __iowrite32_copy(to, from, count)

Normally we'd make this:

#define __iowrite32_copy __iowrite32_copy

... so that it's clear it's just providing the preprocessor symbol, and doesn't have to be updated if the prototype changes.

[...]

Quoted 1 line

+#define __iowrite64_copy(to, from, count) __iowrite64_copy(to, from, count)

Likewise here.

Quoted 6 lines · Mark Rutland

Quoted 1 line

+#define __iowrite32_copy(to, from, count) __iowrite32_copy(to, from, count)

Normally we'd make this:

#define __iowrite32_copy __iowrite32_copy

I can fold these two changes in.

Quoted 39 lines · Arnd Bergmann

From: Arnd Bergmann <[email protected]>

In some configurations __const_iowrite32_copy() does not get inlined and gcc runs into the BUILD_BUG():

In file included from <command-line>:
In function '__const_memcpy_toio_aligned32',

    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:203:3,
    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:199:20:

include/linux/compiler_types.h:487:45: error: call to '__compiletime_assert_538' declared with attribute error: BUILD_BUG failed
487 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^
include/linux/compiler_types.h:468:25: note: in definition of macro '__compiletime_assert'

  468 |                         prefix ## suffix();                             \
      |                         ^~~~~~
include/linux/compiler_types.h:487:9: note: in expansion of macro '_compiletime_assert'
  487 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
   59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
      |                     ^~~~~~~~~~~~~~~~
arch/arm64/include/asm/io.h:193:17: note: in expansion of macro 'BUILD_BUG'
  193 |                 BUILD_BUG();
      |                 ^~~~~~~~~

Move the check for constant arguments into the inline function to ensure it is still constant if the compiler decides against inlining it, and mark them as __always_inline to override the logic that sometimes leads to the compiler not producing the simplified output.

Note that either the __always_inline annotation or the check for a constant value are sufficient here, but combining the two looks cleaner as it also avoids the macro. With clang-8 and older, the macro was still needed, but all versions of gcc and clang can reliably perform constant folding here.

Quoted 2 lines

Fixes ead79118dae6 ("arm64/io: Provide a WC friendly __iowriteXX_copy()")

Signed-off-by Arnd Bergmann <[email protected]>

I have a trivial nit below, but either way this looks good to me, so regardless of that:

Reviewed-by Mark Rutland <[email protected]>

In some configurations __const_iowrite32_copy() does not get inlined and gcc runs into the BUILD_BUG():

In file included from <command-line>:
In function '__const_memcpy_toio_aligned32',

    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:203:3,
    inlined from '__const_iowrite32_copy' at arch/arm64/include/asm/io.h:199:20:

include/linux/compiler_types.h:487:45: error: call to '__compiletime_assert_538' declared with attribute error: BUILD_BUG failed
487 | _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
| ^
include/linux/compiler_types.h:468:25: note: in definition of macro '__compiletime_assert'

  468 |                         prefix ## suffix();                             \
      |                         ^~~~~~
include/linux/compiler_types.h:487:9: note: in expansion of macro '_compiletime_assert'
  487 |         _compiletime_assert(condition, msg, __compiletime_assert_, __COUNTER__)
      |         ^~~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:39:37: note: in expansion of macro 'compiletime_assert'
   39 | #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
      |                                     ^~~~~~~~~~~~~~~~~~
include/linux/build_bug.h:59:21: note: in expansion of macro 'BUILD_BUG_ON_MSG'
   59 | #define BUILD_BUG() BUILD_BUG_ON_MSG(1, "BUILD_BUG failed")
      |                     ^~~~~~~~~~~~~~~~
arch/arm64/include/asm/io.h:193:17: note: in expansion of macro 'BUILD_BUG'
  193 |                 BUILD_BUG();
      |                 ^~~~~~~~~

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