[PATCH v2 1/6] MIPS: Sync after cacheflush on BMIPS processors

[Kevin Cernekee]

On BMIPS processors, cache writeback operations may complete before the
data has actually been written out to memory.  Subsequent uncached reads
(or I/O operations) may see stale data unless a sync instruction is
executed after the writeback loop.

Signed-off-by: Kevin Cernekee <cernekee@xxxxxxxxx>
---
 arch/mips/include/asm/hazards.h |   21 +++++++++++++++++++++
 arch/mips/mm/c-r4k.c            |    5 +++++
 2 files changed, 26 insertions(+), 0 deletions(-)

diff --git a/arch/mips/include/asm/hazards.h b/arch/mips/include/asm/hazards.h
index 4e33216..655da05 100644
--- a/arch/mips/include/asm/hazards.h
+++ b/arch/mips/include/asm/hazards.h
@@ -270,4 +270,25 @@ ASMMACRO(disable_fpu_hazard,
 )
 #endif
 
+/*
+ * Some processors will "pipeline" cache writeback operations, and need an
+ * extra sync instruction to ensure that they are actually flushed out to
+ * memory.  Performing an uncached read (or an I/O operation) without the
+ * flush may cause stale data to be fetched.
+ */
+
+#if defined(CONFIG_CPU_BMIPS3300) || defined(CONFIG_CPU_BMIPS4350) || \
+    defined(CONFIG_CPU_BMIPS4380) || defined(CONFIG_CPU_BMIPS5000)
+
+#define cacheflush_hazard()						\
+do {									\
+	__sync();							\
+} while (0)
+
+#else
+
+#define cacheflush_hazard() do { } while (0)
+
+#endif
+
 #endif /* _ASM_HAZARDS_H */
diff --git a/arch/mips/mm/c-r4k.c b/arch/mips/mm/c-r4k.c
index b4923a7..6c113cd 100644
--- a/arch/mips/mm/c-r4k.c
+++ b/arch/mips/mm/c-r4k.c
@@ -33,6 +33,7 @@
 #include <asm/mmu_context.h>
 #include <asm/war.h>
 #include <asm/cacheflush.h> /* for run_uncached() */
+#include <asm/hazards.h>
 
 
 /*
@@ -604,6 +605,7 @@ static void r4k_dma_cache_wback_inv(unsigned long addr, unsigned long size)
 			r4k_blast_scache();
 		else
 			blast_scache_range(addr, addr + size);
+		cacheflush_hazard();
 		return;
 	}
 
@@ -620,6 +622,7 @@ static void r4k_dma_cache_wback_inv(unsigned long addr, unsigned long size)
 	}
 
 	bc_wback_inv(addr, size);
+	cacheflush_hazard();
 }
 
 static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
@@ -647,6 +650,7 @@ static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 				 (addr + size - 1) & almask);
 			blast_inv_scache_range(addr, addr + size);
 		}
+		cacheflush_hazard();
 		return;
 	}
 
@@ -663,6 +667,7 @@ static void r4k_dma_cache_inv(unsigned long addr, unsigned long size)
 	}
 
 	bc_inv(addr, size);
+	cacheflush_hazard();
 }
 #endif /* CONFIG_DMA_NONCOHERENT */
 
-- 
1.7.0.4

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