[RFC] ARM: Make CPU_DCACHE_DISABLE depend on !SMP

Florian Fainelli
2015-01-08T02:11:28Z

Enabling CPU_DCACHE_DISABLE on a SMP capable system will prevent the
kernel from booting because of the following ldrex instruction in
arch_spin_lock:

(gdb) x/10i $pc
=> 0xc053cfa8 <_raw_spin_lock+4>: ldrex r3, [r0]
0xc053cfac <_raw_spin_lock+8>: add r2, r3, #65536 ; 0x10000

which is taken by the very first printk call:

at /home/fainelli/work/linux/arch/arm/include/asm/spinlock.h:65
fmt=0xc0637650 "\001\066Booting Linux on physical CPU 0x%x\n", args=<incomplete type>)
at kernel/printk/printk.c:1525
fmt=0xc05370f4 <printk+52> "\024\320\215\342\004\340\235\344\020\320\215\342\036\377/\341\017") at kernel/printk/printk.c:1688

ldrex requires exclusive monitor(s) (local or global) which are no longer
working when the Data cache is disabled in CP15 and will just hang the CPU
there.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
---
arch/arm/mm/Kconfig | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 03823e784f63..09245fd1e900 100644
--- a/arch/arm/mm/Kconfig
+++ b/arch/arm/mm/Kconfig
@@ -738,7 +738,7 @@ config CPU_ICACHE_DISABLE

config CPU_DCACHE_DISABLE
bool "Disable D-Cache (C-bit)"
- depends on CPU_CP15
+ depends on CPU_CP15 && !SMP
help
Say Y here to disable the processor data cache. Unless
you have a reason not to or are unsure, say N.
--
2.1.0