net: pcs: xpcs: Add fwnode-based descriptor creation method

It's now possible to have the DW XPCS device defined as a standard
platform device for instance in the platform DT-file. Although that
functionality is useless unless there is a way to have the device found by
the client drivers (STMMAC/DW *MAC, NXP SJA1105 Eth Switch, etc). Provide
such ability by means of the xpcs_create_fwnode() method. It needs to be
called with the device DW XPCS fwnode instance passed. That node will be
then used to find the MDIO-device instance in order to create the DW XPCS
descriptor.

Note the method semantics and name is similar to what has been recently
introduced in the Lynx PCS driver.

Signed-off-by: Serge Semin <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/net/pcs/pcs-xpcs.c

···
 #include <linux/delay.h>
 #include <linux/pcs/pcs-xpcs.h>
 #include <linux/mdio.h>
+#include <linux/phy.h>
 #include <linux/phylink.h>
+#include <linux/property.h>
 
 #include "pcs-xpcs.h"
 
···
 	return ERR_PTR(ret);
 }
 
+/**
+ * xpcs_create_mdiodev() - create a DW xPCS instance with the MDIO @addr
+ * @bus: pointer to the MDIO-bus descriptor for the device to be looked at
+ * @addr: device MDIO-bus ID
+ * @interface: requested PHY interface
+ *
+ * Return: a pointer to the DW XPCS handle if successful, otherwise -ENODEV if
+ * the PCS device couldn't be found on the bus and other negative errno related
+ * to the data allocation and MDIO-bus communications.
+ */
 struct dw_xpcs *xpcs_create_mdiodev(struct mii_bus *bus, int addr,
 				    phy_interface_t interface)
 {
···
 	return xpcs;
 }
 EXPORT_SYMBOL_GPL(xpcs_create_mdiodev);
+
+/**
+ * xpcs_create_fwnode() - Create a DW xPCS instance from @fwnode
+ * @fwnode: fwnode handle poining to the DW XPCS device
+ * @interface: requested PHY interface
+ *
+ * Return: a pointer to the DW XPCS handle if successful, otherwise -ENODEV if
+ * the fwnode device is unavailable or the PCS device couldn't be found on the
+ * bus, -EPROBE_DEFER if the respective MDIO-device instance couldn't be found,
+ * other negative errno related to the data allocations and MDIO-bus
+ * communications.
+ */
+struct dw_xpcs *xpcs_create_fwnode(struct fwnode_handle *fwnode,
+				   phy_interface_t interface)
+{
+	struct mdio_device *mdiodev;
+	struct dw_xpcs *xpcs;
+
+	if (!fwnode_device_is_available(fwnode))
+		return ERR_PTR(-ENODEV);
+
+	mdiodev = fwnode_mdio_find_device(fwnode);
+	if (!mdiodev)
+		return ERR_PTR(-EPROBE_DEFER);
+
+	xpcs = xpcs_create(mdiodev, interface);
+
+	/* xpcs_create() has taken a refcount on the mdiodev if it was
+	 * successful. If xpcs_create() fails, this will free the mdio
+	 * device here. In any case, we don't need to hold our reference
+	 * anymore, and putting it here will allow mdio_device_put() in
+	 * xpcs_destroy() to automatically free the mdio device.
+	 */
+	mdio_device_put(mdiodev);
+
+	return xpcs;
+}
+EXPORT_SYMBOL_GPL(xpcs_create_fwnode);
 
 void xpcs_destroy(struct dw_xpcs *xpcs)
 {

include/linux/pcs/pcs-xpcs.h

···
 #define __LINUX_PCS_XPCS_H
 
 #include <linux/clk.h>
+#include <linux/fwnode.h>
 #include <linux/mdio.h>
 #include <linux/phy.h>
 #include <linux/phylink.h>
···
 		    int enable);
 struct dw_xpcs *xpcs_create_mdiodev(struct mii_bus *bus, int addr,
 				    phy_interface_t interface);
+struct dw_xpcs *xpcs_create_fwnode(struct fwnode_handle *fwnode,
+				   phy_interface_t interface);
 void xpcs_destroy(struct dw_xpcs *xpcs);
 
 #endif /* __LINUX_PCS_XPCS_H */