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MIPS: DMA: For BMIPS5000 cores flush region just like non-coherent R1000

Subject: MIPS: DMA: For BMIPS5000 cores flush region just like non-coherent R10000
From: Jim Quinlan <>
Date: Tue, 27 Aug 2013 16:57:51 -0400
commit f86f55d3ad21b21b736bdeb29bee0f0937b77138 upstream.

The BMIPS5000 (Zephyr) processor utilizes instruction speculation. A
stale misprediction address in either the JTB or the CRS may trigger
a prefetch inside a region that is currently being used by a DMA engine,
which is not IO-coherent.  This prefetch will fetch a line into the
scache, and that line will soon become stale (ie wrong) during/after the
DMA.  Mayhem ensues.

In dma-default.c, the r10000 is handled as a special case in the same way
that we want to handle Zephyr.  So we generalize the exception cases into
a function, and include Zephyr as one of the processors that needs this
special care.

Signed-off-by: Jim Quinlan <>
Signed-off-by: Ralf Baechle <>
Signed-off-by: Luis Henriques <>
 arch/mips/mm/dma-default.c | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index 3fab204..0eea2d2 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
@@ -30,16 +30,20 @@ static inline struct page *dma_addr_to_page(struct device 

+ * The affected CPUs below in 'cpu_needs_post_dma_flush()' can
+ * speculatively fill random cachelines with stale data at any time,
+ * requiring an extra flush post-DMA.
+ *
  * Warning on the terminology - Linux calls an uncached area coherent;
  * MIPS terminology calls memory areas with hardware maintained coherency
  * coherent.
-static inline int cpu_is_noncoherent_r10000(struct device *dev)
+static inline int cpu_needs_post_dma_flush(struct device *dev)
        return !plat_device_is_coherent(dev) &&
               (current_cpu_type() == CPU_R10000 ||
-              current_cpu_type() == CPU_R12000);
+               current_cpu_type() == CPU_R12000 ||
+               current_cpu_type() == CPU_BMIPS5000);

 static gfp_t massage_gfp_flags(const struct device *dev, gfp_t gfp)
@@ -209,7 +213,7 @@ static inline void __dma_sync(struct page *page,
 static void mips_dma_unmap_page(struct device *dev, dma_addr_t dma_addr,
        size_t size, enum dma_data_direction direction, struct dma_attrs *attrs)
-       if (cpu_is_noncoherent_r10000(dev))
+       if (cpu_needs_post_dma_flush(dev))
                __dma_sync(dma_addr_to_page(dev, dma_addr),
                           dma_addr & ~PAGE_MASK, size, direction);

@@ -260,7 +264,7 @@ static void mips_dma_unmap_sg(struct device *dev, struct 
scatterlist *sg,
 static void mips_dma_sync_single_for_cpu(struct device *dev,
        dma_addr_t dma_handle, size_t size, enum dma_data_direction direction)
-       if (cpu_is_noncoherent_r10000(dev))
+       if (cpu_needs_post_dma_flush(dev))
                __dma_sync(dma_addr_to_page(dev, dma_handle),
                           dma_handle & ~PAGE_MASK, size, direction);
@@ -281,7 +285,7 @@ static void mips_dma_sync_sg_for_cpu(struct device *dev,

        /* Make sure that gcc doesn't leave the empty loop body.  */
        for (i = 0; i < nelems; i++, sg++) {
-               if (cpu_is_noncoherent_r10000(dev))
+               if (cpu_needs_post_dma_flush(dev))
                        __dma_sync(sg_page(sg), sg->offset, sg->length,

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