soundwire: cadence_master: filter out bad interrupts

If somehow we read the interrupt status while the IP is not powered
the result is probably undefined or 0xffffffff. We do know that some
of the bits are reserved and read as zero, so use as a filter to
discard invalid configurations.
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20200110215731.30747-2-pierre-louis.bossart@linux.intel.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/soundwire/cadence_master.c

@@ -74,6 +74,7 @@ MODULE_PARM_DESC(cdns_mcp_int_mask, "Cadence MCP IntMask");
 #define CDNS_MCP_INTMASK			0x48
 
 #define CDNS_MCP_INT_IRQ			BIT(31)
+#define CDNS_MCP_INT_RESERVED1			GENMASK(30, 17)
 #define CDNS_MCP_INT_WAKEUP			BIT(16)
 #define CDNS_MCP_INT_SLAVE_RSVD			BIT(15)
 #define CDNS_MCP_INT_SLAVE_ALERT		BIT(14)
@@ -85,10 +86,12 @@ MODULE_PARM_DESC(cdns_mcp_int_mask, "Cadence MCP IntMask");
 #define CDNS_MCP_INT_DATA_CLASH			BIT(9)
 #define CDNS_MCP_INT_PARITY			BIT(8)
 #define CDNS_MCP_INT_CMD_ERR			BIT(7)
+#define CDNS_MCP_INT_RESERVED2			GENMASK(6, 4)
 #define CDNS_MCP_INT_RX_NE			BIT(3)
 #define CDNS_MCP_INT_RX_WL			BIT(2)
 #define CDNS_MCP_INT_TXE			BIT(1)
 #define CDNS_MCP_INT_TXF			BIT(0)
+#define CDNS_MCP_INT_RESERVED (CDNS_MCP_INT_RESERVED1 | CDNS_MCP_INT_RESERVED2)
 
 #define CDNS_MCP_INTSET				0x4C
 
@@ -705,6 +708,10 @@ irqreturn_t sdw_cdns_irq(int irq, void *dev_id)
 
 	int_status = cdns_readl(cdns, CDNS_MCP_INTSTAT);
 
+	/* check for reserved values read as zero */
+	if (int_status & CDNS_MCP_INT_RESERVED)
+		return IRQ_NONE;
+
 	if (!(int_status & CDNS_MCP_INT_IRQ))
 		return IRQ_NONE;