m68k: Fix invalid RMW_INSNS on CPUs that lack CAS

When enabling CONFIG_RMW_INSNS in e.g. a Coldfire build:

    {standard input}:3068: Error: invalid instruction for this architecture; needs 68020 or higher (68020 [68k, 68ec020], 68030 [68ec030], 68040 [68ec040], 68060 [68ec060]) -- statement `casl %d4,%d0,(%a6)' ignored

Fix this by (a) adding a new config symbol to track if support for any
CPU that lacks the CAS instruction is enabled, and (b) making
CONFIG_RMW_INSNS depend on the new symbol not being set.

Fixes: 0e152d80507b75c0 ("m68k: reorganize Kconfig options to improve mmu/non-mmu selections")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20210725104413.318932-1-geert@linux-m68k.org

diff --git a/arch/m68k/Kconfig.cpu b/arch/m68k/Kconfig.cpu
index 29e9463..277d61a 100644 (file)
--- a/arch/m68k/Kconfig.cpu
+++ b/arch/m68k/Kconfig.cpu
@@ -26,6 +26,7 @@ config COLDFIRE
        bool "Coldfire CPU family support"
        select ARCH_HAVE_CUSTOM_GPIO_H
        select CPU_HAS_NO_BITFIELDS
+       select CPU_HAS_NO_CAS
        select CPU_HAS_NO_MULDIV64
        select GENERIC_CSUM
        select GPIOLIB
@@ -39,6 +40,7 @@ config M68000
        bool
        depends on !MMU
        select CPU_HAS_NO_BITFIELDS
+       select CPU_HAS_NO_CAS
        select CPU_HAS_NO_MULDIV64
        select CPU_HAS_NO_UNALIGNED
        select GENERIC_CSUM
@@ -54,6 +56,7 @@ config M68000
 config MCPU32
        bool
        select CPU_HAS_NO_BITFIELDS
+       select CPU_HAS_NO_CAS
        select CPU_HAS_NO_UNALIGNED
        select CPU_NO_EFFICIENT_FFS
        help
@@ -383,7 +386,7 @@ config ADVANCED
 
 config RMW_INSNS
        bool "Use read-modify-write instructions"
-       depends on ADVANCED
+       depends on ADVANCED && !CPU_HAS_NO_CAS
        help
          This allows to use certain instructions that work with indivisible
          read-modify-write bus cycles. While this is faster than the
@@ -450,6 +453,9 @@ config M68K_L2_CACHE
 config CPU_HAS_NO_BITFIELDS
        bool
 
+config CPU_HAS_NO_CAS
+       bool
+
 config CPU_HAS_NO_MULDIV64
        bool