From: Florian Fainelli <f.fainelli@gmail.com>
Date: Fri, 9 Jan 2015 18:34:43 +0000 (+0100)
Subject: ARM: 8276/1: Make CPU_DCACHE_DISABLE depend on !SMP
X-Git-Tag: v4.14-rc1~5488^2~2^3~2
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=e1e2f6e4c5759aab3a8cfb1a0c19017ea770dfd2;p=platform%2Fkernel%2Flinux-rpi.git

ARM: 8276/1: Make CPU_DCACHE_DISABLE depend on !SMP

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 " 01 66Booting Linux on physical CPU 0x%xn", args=<incomplete type>)
    at kernel/printk/printk.c:1525
    fmt=0xc05370f4 <printk+52> " 24320215342 04340235344 20320215342 36377/341 17") 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.

Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
---

diff --git a/arch/arm/mm/Kconfig b/arch/arm/mm/Kconfig
index 9b4f29e..133ecff 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.