net: mtk_eth_soc: add definitions for PCS

As a result of help from Frank Wunderlich to investigate and test, we
know a bit more about the PCS on the Mediatek platforms. Update the
definitions from this investigation.

This PCS appears similar, but not identical to the Lynx PCS.

Although not included in this patch, but for future reference, the PHY
ID registers at offset 4 read as 0x4d544950 'MTIP'.
Signed-off-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mediatek/mtk_eth_soc.h

@@ -466,8 +466,10 @@
 #define ETHSYS_DMA_AG_MAP_PPE	BIT(2)
 
 /* SGMII subsystem config registers */
-/* Register to auto-negotiation restart */
+/* BMCR (low 16) BMSR (high 16) */
 #define SGMSYS_PCS_CONTROL_1	0x0
+#define SGMII_BMCR		GENMASK(15, 0)
+#define SGMII_BMSR		GENMASK(31, 16)
 #define SGMII_AN_RESTART	BIT(9)
 #define SGMII_ISOLATE		BIT(10)
 #define SGMII_AN_ENABLE		BIT(12)
@@ -477,13 +479,18 @@
 #define SGMII_PCS_FAULT		BIT(23)
 #define SGMII_AN_EXPANSION_CLR	BIT(30)
 
+#define SGMSYS_PCS_ADVERTISE	0x8
+#define SGMII_ADVERTISE		GENMASK(15, 0)
+#define SGMII_LPA		GENMASK(31, 16)
+
 /* Register to programmable link timer, the unit in 2 * 8ns */
 #define SGMSYS_PCS_LINK_TIMER	0x18
-#define SGMII_LINK_TIMER_DEFAULT	(0x186a0 & GENMASK(19, 0))
+#define SGMII_LINK_TIMER_MASK	GENMASK(19, 0)
+#define SGMII_LINK_TIMER_DEFAULT	(0x186a0 & SGMII_LINK_TIMER_MASK)
 
 /* Register to control remote fault */
 #define SGMSYS_SGMII_MODE		0x20
-#define SGMII_IF_MODE_BIT0		BIT(0)
+#define SGMII_IF_MODE_SGMII		BIT(0)
 #define SGMII_SPEED_DUPLEX_AN		BIT(1)
 #define SGMII_SPEED_MASK		GENMASK(3, 2)
 #define SGMII_SPEED_10			FIELD_PREP(SGMII_SPEED_MASK, 0)