[libata] sata_mv: don't touch reserved bits in EDMA config register

The code in mv_edma_cfg() reflected its 60xx origins, by doing things
[slightly] incorrectly on the older 50xx and newer 6042/7042 chips.

Clean up the EDMA configuration setup such that, each chip family
carefully initializes its own EDMA setup.

Signed-off-by: Jeff Garzik <[e-mail]>

drivers/ata/sata_mv.c

···
 	u32 cfg = readl(port_mmio + EDMA_CFG_OFS);
 
 	/* set up non-NCQ EDMA configuration */
-	cfg &= ~0x1f;		/* clear queue depth */
-	cfg &= ~EDMA_CFG_NCQ;	/* clear NCQ mode */
 	cfg &= ~(1 << 9);	/* disable equeue */
 
-	if (IS_GEN_I(hpriv))
+	if (IS_GEN_I(hpriv)) {
+		cfg &= ~0x1f;		/* clear queue depth */
 		cfg |= (1 << 8);	/* enab config burst size mask */
+	}
 
-	else if (IS_GEN_II(hpriv))
+	else if (IS_GEN_II(hpriv)) {
+		cfg &= ~0x1f;		/* clear queue depth */
 		cfg |= EDMA_CFG_RD_BRST_EXT | EDMA_CFG_WR_BUFF_LEN;
+		cfg &= ~(EDMA_CFG_NCQ | EDMA_CFG_NCQ_GO_ON_ERR); /* clear NCQ */
+	}
 
 	else if (IS_GEN_IIE(hpriv)) {
-		cfg |= (1 << 23);	/* dis RX PM port mask */
-		cfg &= ~(1 << 16);	/* dis FIS-based switching (for now) */
+		cfg |= (1 << 23);	/* do not mask PM field in rx'd FIS */
+		cfg |= (1 << 22);	/* enab 4-entry host queue cache */
 		cfg &= ~(1 << 19);	/* dis 128-entry queue (for now?) */
 		cfg |= (1 << 18);	/* enab early completion */
-		cfg |= (1 << 17);	/* enab host q cache */
-		cfg |= (1 << 22);	/* enab cutthrough */
+		cfg |= (1 << 17);	/* enab cut-through (dis stor&forwrd) */
+		cfg &= ~(1 << 16);	/* dis FIS-based switching (for now) */
+		cfg &= ~(EDMA_CFG_NCQ | EDMA_CFG_NCQ_GO_ON_ERR); /* clear NCQ */
 	}
 
 	writelfl(cfg, port_mmio + EDMA_CFG_OFS);