MIPS/alchemy: factor out the DMA coherent setup

Factor out a alchemy_dma_coherent helper that determines if the platform
is DMA coherent.  Also stop initializing the hw_coherentio variable, given
that is only ever set to a non-zero value by the malta setup code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

Author: Christoph Hellwig

arch/mips/alchemy/common/setup.c

@@ -37,6 +37,23 @@
 extern void __init board_setup(void);
 extern void __init alchemy_set_lpj(void);
 
+static bool alchemy_dma_coherent(void)
+{
+	switch (alchemy_get_cputype()) {
+	case ALCHEMY_CPU_AU1000:
+	case ALCHEMY_CPU_AU1500:
+	case ALCHEMY_CPU_AU1100:
+		return false;
+	case ALCHEMY_CPU_AU1200:
+		/* Au1200 AB USB does not support coherent memory */
+		if ((read_c0_prid() & PRID_REV_MASK) == 0)
+			return false;
+		return true;
+	default:
+		return true;
+	}
+}
+
 void __init plat_mem_setup(void)
 {
 	alchemy_set_lpj();
@@ -48,20 +65,8 @@ void __init plat_mem_setup(void)
 		/* Clear to obtain best system bus performance */
 		clear_c0_config(1 << 19); /* Clear Config[OD] */
 
-	hw_coherentio = 0;
-	coherentio = IO_COHERENCE_ENABLED;
-	switch (alchemy_get_cputype()) {
-	case ALCHEMY_CPU_AU1000:
-	case ALCHEMY_CPU_AU1500:
-	case ALCHEMY_CPU_AU1100:
-		coherentio = IO_COHERENCE_DISABLED;
-		break;
-	case ALCHEMY_CPU_AU1200:
-		/* Au1200 AB USB does not support coherent memory */
-		if (0 == (read_c0_prid() & PRID_REV_MASK))
-			coherentio = IO_COHERENCE_DISABLED;
-		break;
-	}
+	coherentio = alchemy_dma_coherent() ?
+		IO_COHERENCE_ENABLED : IO_COHERENCE_DISABLED;
 
 	board_setup();	/* board specific setup */