phy: add support for the Layerscape SerDes 28G

This patch adds a new generic PHY driver to support the Lynx 28G SerDes
block found on some of the Layerscape SoCs such as LX2160A.
At the moment, only the following Ethernet protocols are supported:
SGMII/1000Base-X and 10GBaseR.

SerDes lanes which are not running an Ethernet protocol or a currently
supported Ethenet protocol will be left as it was configured through the
RCW (Reset Configuration Word) at boot time.

At probe time, the platform driver will read the current
configuration of both PLLs found on a SerDes block and will determine
what protocols are supported using that PLL.

For example, if a PLL is configured to generate a clock net (frate) of
5GHz the only protocols sustained by that PLL are SGMII/1000Base-X
(using a quarter of the full clock rate) and QSGMII using the full clock
net frequency on the lane.

On the .set_mode() callback, the PHY driver will first check if the
requested operating mode (protocol) is even supported by the current PLL
configuration and will error out if not.
Then, the lane is reconfigured to run on the requested protocol.

Signed-off-by: Ioana Ciornei <ioana.ciornei@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

MAINTAINERS

@@ -11333,6 +11333,12 @@ S:	Maintained
 W:	http://linux-test-project.github.io/
 T:	git git://github.com/linux-test-project/ltp.git
 
+LYNX 28G SERDES PHY DRIVER
+M:	Ioana Ciornei <ioana.ciornei@nxp.com>
+L:	netdev@vger.kernel.org
+S:	Supported
+F:	drivers/phy/freescale/phy-fsl-lynx-28g.c
+
 LYNX PCS MODULE
 M:	Ioana Ciornei <ioana.ciornei@nxp.com>
 L:	netdev@vger.kernel.org

drivers/phy/freescale/Kconfig

@@ -22,3 +22,13 @@ config PHY_FSL_IMX8M_PCIE
 	help
 	  Enable this to add support for the PCIE PHY as found on
 	  i.MX8M family of SOCs.
+
+config PHY_FSL_LYNX_28G
+	tristate "Freescale Layerscape Lynx 28G SerDes PHY support"
+	depends on OF
+	select GENERIC_PHY
+	help
+	  Enable this to add support for the Lynx SerDes 28G PHY as
+	  found on NXP's Layerscape platforms such as LX2160A.
+	  Used to change the protocol running on SerDes lanes at runtime.
+	  Only useful for a restricted set of Ethernet protocols.

drivers/phy/freescale/Makefile

@@ -2,3 +2,4 @@
 obj-$(CONFIG_PHY_FSL_IMX8MQ_USB)	+= phy-fsl-imx8mq-usb.o
 obj-$(CONFIG_PHY_MIXEL_MIPI_DPHY)	+= phy-fsl-imx8-mipi-dphy.o
 obj-$(CONFIG_PHY_FSL_IMX8M_PCIE)	+= phy-fsl-imx8m-pcie.o
+obj-$(CONFIG_PHY_FSL_LYNX_28G)		+= phy-fsl-lynx-28g.o