phy: phy-ocelot-serdes: add ability to be used in a non-syscon configuration

The phy-ocelot-serdes module has exclusively been used in a syscon setup,
from an internal CPU. The addition of external control of ocelot switches
via an existing MFD implementation means that syscon is no longer the only
interface that phy-ocelot-serdes will see.

In the MFD configuration, an IORESOURCE_REG resource will exist for the
device. Utilize this resource to be able to function in both syscon and
non-syscon configurations.

Signed-off-by: Colin Foster <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/phy/mscc/phy-ocelot-serdes.c

···
 {
 	struct phy_provider *provider;
 	struct serdes_ctrl *ctrl;
+	struct resource *res;
 	unsigned int i;
 	int ret;
 
···
 
 	ctrl->dev = &pdev->dev;
 	ctrl->regs = syscon_node_to_regmap(pdev->dev.parent->of_node);
+	if (IS_ERR(ctrl->regs)) {
+		/* Fall back to using IORESOURCE_REG, if possible */
+		res = platform_get_resource(pdev, IORESOURCE_REG, 0);
+		if (res)
+			ctrl->regs = dev_get_regmap(ctrl->dev->parent,
+						    res->name);
+	}
+
 	if (IS_ERR(ctrl->regs))
 		return PTR_ERR(ctrl->regs);