ARM: cache: do not crash when the MMU isn't yet setup

Drivers currently cannot implement explicit cache handling and rely on
running the same code before and after mmu_initcall() without crashing.

Depending on the chosen config options, the cache functions are not yet
setup and using them early on ends in a null pointer dereference.

The RPi's mailbox driver is such a case; it requires cache handling once
the MMU is fully set up and yet the RPi setup needs to use the driver to
get the memory size before mem_initcall() and hence mmu_initcall().

Fix this by checking the cache_fns pointer before dereferencing it.

Signed-off-by: Andre Heider <a.heider@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

1 files changed, 12 insertions, 6 deletions

diff --git a/arch/arm/cpu/cache.c b/arch/arm/cpu/cache.c
index 7aab55b6bc..223e3089b2 100644
--- a/arch/arm/cpu/cache.c
+++ b/arch/arm/cpu/cache.c
@@ -41,32 +41,38 @@ DEFINE_CPU_FNS(v7)
 
 void __dma_clean_range(unsigned long start, unsigned long end)
 {
-	cache_fns->dma_clean_range(start, end);
+	if (cache_fns)
+		cache_fns->dma_clean_range(start, end);
 }
 
 void __dma_flush_range(unsigned long start, unsigned long end)
 {
-	cache_fns->dma_flush_range(start, end);
+	if (cache_fns)
+		cache_fns->dma_flush_range(start, end);
 }
 
 void __dma_inv_range(unsigned long start, unsigned long end)
 {
-	cache_fns->dma_inv_range(start, end);
+	if (cache_fns)
+		cache_fns->dma_inv_range(start, end);
 }
 
 void __mmu_cache_on(void)
 {
-	cache_fns->mmu_cache_on();
+	if (cache_fns)
+		cache_fns->mmu_cache_on();
 }
 
 void __mmu_cache_off(void)
 {
-	cache_fns->mmu_cache_off();
+	if (cache_fns)
+		cache_fns->mmu_cache_off();
 }
 
 void __mmu_cache_flush(void)
 {
-	cache_fns->mmu_cache_flush();
+	if (cache_fns)
+		cache_fns->mmu_cache_flush();
 }
 
 int arm_set_cache_functions(void)