MIPS: BMIPS: Flush the readahead cache after DMA.

BMIPS 3300/435x/438x CPUs have a readahead cache that is separate from
the L1/L2.  During a DMA operation, accesses adjacent to a DMA buffer
may cause parts of the DMA buffer to be prefetched into the RAC.  To
avoid possible coherency problems, flush the RAC upon DMA completion.

Derived from Kevin Cernekee's https://patchwork.linux-mips.org/patch/9602/.
Signed-off-by: NRalf Baechle <ralf@linux-mips.org>

arch/mips/include/asm/mach-bmips/dma-coherence.h

@@ -15,6 +15,10 @@
 #ifndef __ASM_MACH_BMIPS_DMA_COHERENCE_H
 #define __ASM_MACH_BMIPS_DMA_COHERENCE_H
 
+#include <asm/bmips.h>
+#include <asm/cpu-type.h>
+#include <asm/cpu.h>
+
 struct device;
 
 extern dma_addr_t plat_map_dma_mem(struct device *dev, void *addr, size_t size);
@@ -47,6 +51,18 @@ static inline int plat_device_is_coherent(struct device *dev)
 
 static inline void plat_post_dma_flush(struct device *dev)
 {
+	void __iomem *cbr = BMIPS_GET_CBR();
+	u32 cfg;
+
+	if (boot_cpu_type() != CPU_BMIPS3300 &&
+	    boot_cpu_type() != CPU_BMIPS4350 &&
+	    boot_cpu_type() != CPU_BMIPS4380)
+		return;
+
+	/* Flush stale data out of the readahead cache */
+	cfg = __raw_readl(cbr + BMIPS_RAC_CONFIG);
+	__raw_writel(cfg | 0x100, cbr + BMIPS_RAC_CONFIG);
+	__raw_readl(cbr + BMIPS_RAC_CONFIG);
 }
 
 #endif /* __ASM_MACH_BMIPS_DMA_COHERENCE_H */