From: Gavin Li <g...@thegavinli.com>
On x86, calling dma_mmap_coherent() on memory allocated with
dma_alloc_coherent() causes the following warning to be issued:
x86/PAT: ... map pfn RAM range req uncached-minus for [mem
0x77f000000-0x77f210fff], got write-back
This occurs because on x86 dma_alloc_coherent() returns normal kernel
memory pages (with a write-back PAT), but dma_mmap_coherent() tries to
map the same pages into userspace with a uncached-minus PAT, even though
there is no need for the mapping to noncached.
This patch ensures that on DMA coherent architectures/devices, memory is
mapped normally rather than as noncached.
Signed-off-by: Gavin Li <g...@thegavinli.com>
---
include/linux/dma-noncoherent.h | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)
diff --git a/include/linux/dma-noncoherent.h b/include/linux/dma-noncoherent.h
index 9741767e400f..40ff11380ec7 100644
--- a/include/linux/dma-noncoherent.h
+++ b/include/linux/dma-noncoherent.h
@@ -31,7 +31,11 @@ long arch_dma_coherent_to_pfn(struct device *dev, void
*cpu_addr,
pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
unsigned long attrs);
#else
-# define arch_dma_mmap_pgprot(dev, prot, attrs) pgprot_noncached(prot)
+static inline pgprot_t arch_dma_mmap_pgprot(struct device *dev, pgprot_t prot,
+ unsigned long attrs)
+{
+ return dev_is_dma_coherent(dev) ? prot : pgprot_noncached(prot);
+}
#endif
#ifdef CONFIG_DMA_NONCOHERENT_CACHE_SYNC
--
2.22.0
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