[RFC PATCH] ARM: Allow lazy cache flushing on ARM11MPCore

[Catalin Marinas]

        (we could actually go a step further for ARM11MPCore as well.
        This patch is not part of the initial cache flush reworking
        series but I'm posting it for comments as well)

The ARM11MPCore doesn't broadcast the cache maintenance operations in
hardware, therefore the flush_dcache_page() currently performs the cache
flushing non-lazily. But since not all drivers call this function after
writing to a page cache page, the kernel needs a different approach like
using read-for-ownership on the CPU flushing the cache to force the
dirty cache lines migration from other CPUs. This way the cache flushing
operation can be done lazily in update_mmu_cache().

Signed-off-by: Catalin Marinas <catalin.marinas at arm.com>
---
 arch/arm/include/asm/smp_plat.h |    9 ---------
 arch/arm/mm/cache-v6.S          |    4 ++++
 arch/arm/mm/flush.c             |    3 +--
 3 files changed, 5 insertions(+), 11 deletions(-)

diff --git a/arch/arm/include/asm/smp_plat.h b/arch/arm/include/asm/smp_plat.h
index 963a338..59303e2 100644
--- a/arch/arm/include/asm/smp_plat.h
+++ b/arch/arm/include/asm/smp_plat.h
@@ -13,13 +13,4 @@ static inline int tlb_ops_need_broadcast(void)
 	return ((read_cpuid_ext(CPUID_EXT_MMFR3) >> 12) & 0xf) < 2;
 }
 
-#if !defined(CONFIG_SMP) || __LINUX_ARM_ARCH__ >= 7
-#define cache_ops_need_broadcast()	0
-#else
-static inline int cache_ops_need_broadcast(void)
-{
-	return ((read_cpuid_ext(CPUID_EXT_MMFR3) >> 12) & 0xf) < 1;
-}
-#endif
-
 #endif
diff --git a/arch/arm/mm/cache-v6.S b/arch/arm/mm/cache-v6.S
index e46ecd8..a4a6840 100644
--- a/arch/arm/mm/cache-v6.S
+++ b/arch/arm/mm/cache-v6.S
@@ -170,6 +170,10 @@ ENDPROC(v6_coherent_kern_range)
 ENTRY(v6_flush_kern_dcache_area)
 	add	r1, r0, r1
 1:
+#ifdef CONFIG_SMP
+	/* no cache maintenance broadcasting on ARM11MPCore */
+	ldr	r2, [r0]			@ read for ownership
+#endif
 #ifdef HARVARD_CACHE
 	mcr	p15, 0, r0, c7, c14, 1		@ clean & invalidate D line
 #else
diff --git a/arch/arm/mm/flush.c b/arch/arm/mm/flush.c
index 5abab9a..7d8b261 100644
--- a/arch/arm/mm/flush.c
+++ b/arch/arm/mm/flush.c
@@ -243,8 +243,7 @@ void flush_dcache_page(struct page *page)
 
 	mapping = page_mapping(page);
 
-	if (!cache_ops_need_broadcast() &&
-	    !PageHighMem(page) && mapping && !mapping_mapped(mapping))
+	if (!PageHighMem(page) && mapping && !mapping_mapped(mapping))
 		clear_bit(PG_dcache_clean, &page->flags);
 	else {
 		__flush_dcache_page(mapping, page);