cpsw: add a DT field for the active time stamping port

Because time stamping on both external ports of the switch simultaneously
is positively useless from the application's point of view, this patch
provides a DT configuration method to choose the active port.
Signed-off-by: Richard Cochran <richardcochran@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Documentation/devicetree/bindings/net/cpsw.txt

@@ -23,6 +23,7 @@ Required properties:
 - mac_control		: Specifies Default MAC control register content
 			  for the specific platform
 - slaves		: Specifies number for slaves
+- cpts_active_slave	: Specifies the slave to use for time stamping
 - slave_reg_ofs		: Specifies slave register offset
 - sliver_reg_ofs	: Specifies slave sliver register offset
 - phy_id		: Specifies slave phy id
@@ -60,6 +61,7 @@ Examples:
 		rx_descs = <64>;
 		mac_control = <0x20>;
 		slaves = <2>;
+		cpts_active_slave = <0>;
 		cpsw_emac0: slave@0 {
 			slave_reg_ofs = <0x200>;
 			sliver_reg_ofs = <0xd80>;
@@ -95,6 +97,7 @@ Examples:
 		rx_descs = <64>;
 		mac_control = <0x20>;
 		slaves = <2>;
+		cpts_active_slave = <0>;
 		cpsw_emac0: slave@0 {
 			slave_reg_ofs = <0x200>;
 			sliver_reg_ofs = <0xd80>;

drivers/net/ethernet/ti/cpsw.c

@@ -847,6 +847,13 @@ static int cpsw_probe_dt(struct cpsw_platform_data *data,
 	}
 	data->slaves = prop;
 
+	if (of_property_read_u32(node, "cpts_active_slave", &prop)) {
+		pr_err("Missing cpts_active_slave property in the DT.\n");
+		ret = -EINVAL;
+		goto error_ret;
+	}
+	data->cpts_active_slave = prop;
+
 	data->slave_data = kzalloc(sizeof(struct cpsw_slave_data) *
 				   data->slaves, GFP_KERNEL);
 	if (!data->slave_data) {

include/linux/platform_data/cpsw.h

@@ -33,6 +33,7 @@ struct cpsw_platform_data {
 
 	u32	slaves;		/* number of slave cpgmac ports */
 	struct cpsw_slave_data	*slave_data;
+	u32	cpts_active_slave; /* time stamping slave */
 
 	u32	ale_reg_ofs;	/* address lookup engine reg offset */
 	u32	ale_entries;	/* ale table size */