MIPS: Add option to disable software I/O coherency.

Some MIPS controllers have hardware I/O coherency. This patch
detects those and turns off software coherency. A new kernel
command line option also allows the user to manually turn
software coherency on or off.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>

1 files changed, 23 insertions, 2 deletions

diff --git a/arch/mips/mm/dma-default.c b/arch/mips/mm/dma-default.c
index f9ef83829a52..caf92ecb37d6 100644
--- a/arch/mips/mm/dma-default.c
+++ b/arch/mips/mm/dma-default.c
@@ -22,6 +22,26 @@
 
 #include <dma-coherence.h>
 
+int coherentio = 0;	/* User defined DMA coherency from command line. */
+EXPORT_SYMBOL_GPL(coherentio);
+int hw_coherentio = 0;	/* Actual hardware supported DMA coherency setting. */
+
+static int __init setcoherentio(char *str)
+{
+	coherentio = 1;
+	pr_info("Hardware DMA cache coherency (command line)\n");
+	return 0;
+}
+early_param("coherentio", setcoherentio);
+
+static int __init setnocoherentio(char *str)
+{
+	coherentio = 0;
+	pr_info("Software DMA cache coherency (command line)\n");
+	return 0;
+}
+early_param("nocoherentio", setnocoherentio);
+
 static inline struct page *dma_addr_to_page(struct device *dev,
 	dma_addr_t dma_addr)
 {
@@ -115,7 +135,8 @@ static void *mips_dma_alloc_coherent(struct device *dev, size_t size,
 
 		if (!plat_device_is_coherent(dev)) {
 			dma_cache_wback_inv((unsigned long) ret, size);
-			ret = UNCAC_ADDR(ret);
+			if (!hw_coherentio)
+				ret = UNCAC_ADDR(ret);
 		}
 	}
 
@@ -142,7 +163,7 @@ static void mips_dma_free_coherent(struct device *dev, size_t size, void *vaddr,
 
 	plat_unmap_dma_mem(dev, dma_handle, size, DMA_BIDIRECTIONAL);
 
-	if (!plat_device_is_coherent(dev))
+	if (!plat_device_is_coherent(dev) && !hw_coherentio)
 		addr = CAC_ADDR(addr);
 
 	free_pages(addr, get_order(size));