MIPS: SmartMIPS: Disable assembler warnings

The kernel code overrides the default ISA as passed by the compiler
in quite a few places. This has unfortunate side effects when smartmips
is enabled leading to hundreds of warnings during build such as:

{standard input}: Assembler messages:
{standard input}:411: Warning: the `smartmips' extension requires MIPS32
revision 1 or greater
{standard input}: Assembler messages:
{standard input}:43: Warning: the 64-bit MIPS architecture does not support the
`smartmips' extension
[...]

Until the kernel code is fixed properly (if possible), disable all the
assembler warning messages to make the build logs readable again.
This has no runtime side effects but it makes it easier to spot
more critical warnings and problems during build.
Signed-off-by: Markos Chandras <markos.chandras@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/7356/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Makefile

@@ -113,7 +113,16 @@ predef-le += -DMIPSEL -D_MIPSEL -D__MIPSEL -D__MIPSEL__
 cflags-$(CONFIG_CPU_BIG_ENDIAN)		+= $(shell $(CC) -dumpmachine |grep -q 'mips.*el-.*' && echo -EB $(undef-all) $(predef-be))
 cflags-$(CONFIG_CPU_LITTLE_ENDIAN)	+= $(shell $(CC) -dumpmachine |grep -q 'mips.*el-.*' || echo -EL $(undef-all) $(predef-le))
 
-cflags-$(CONFIG_CPU_HAS_SMARTMIPS)	+= $(call cc-option,-msmartmips)
+# For smartmips configurations, there are hundreds of warnings due to ISA overrides
+# in assembly and header files. smartmips is only supported for MIPS32r1 onwards
+# and there is no support for 64-bit. Various '.set mips2' or '.set mips3' or
+# similar directives in the kernel will spam the build logs with the following warnings:
+# Warning: the `smartmips' extension requires MIPS32 revision 1 or greater
+# or
+# Warning: the 64-bit MIPS architecture does not support the `smartmips' extension
+# Pass -Wa,--no-warn to disable all assembler warnings until the kernel code has
+# been fixed properly.
+cflags-$(CONFIG_CPU_HAS_SMARTMIPS)	+= $(call cc-option,-msmartmips) -Wa,--no-warn
 cflags-$(CONFIG_CPU_MICROMIPS) += $(call cc-option,-mmicromips)
 
 cflags-$(CONFIG_SB1XXX_CORELIS)	+= $(call cc-option,-mno-sched-prolog) \