dsa: add support for the Marvell 88E6131 switch chip

Add support for the Marvell 88E6131 switch chip.  This chip only
supports the original (ethertype-less) DSA tagging format.

On the 88E6131, there is a PHY Polling Unit (PPU) which has exclusive
access to each of the PHYs's MII management registers.  If we want to
talk to the PHYs from software, we have to disable the PPU and wait
for it to complete its current transaction before we can do so, and we
need to re-enable the PPU afterwards to make sure that the switch will
notice changes in link state and speed on the individual ports as they
occur.

Since disabling the PPU is rather slow, and since MII management
accesses are typically done in bursts, this patch keeps the PPU disabled
for 10ms after a software access completes.  This makes handling the
PPU slightly more complex, but speeds up something like running ethtool
on one of the switch slave interfaces from ~300ms to ~30ms on typical
hardware.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Tested-by: Nicolas Pitre <nico@marvell.com>
Tested-by: Peter van Valderen <linux@ddcrew.com>
Tested-by: Dirk Teurlings <dirk@upexia.nl>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/dsa/Kconfig

@@ -24,6 +24,19 @@ config NET_DSA_MV88E6XXX
 	bool
 	default n
 
+config NET_DSA_MV88E6XXX_NEED_PPU
+	bool
+	default n
+
+config NET_DSA_MV88E6131
+	bool "Marvell 88E6131 ethernet switch chip support"
+	select NET_DSA_MV88E6XXX
+	select NET_DSA_MV88E6XXX_NEED_PPU
+	select NET_DSA_TAG_DSA
+	---help---
+	  This enables support for the Marvell 88E6131 ethernet switch
+	  chip.
+
 config NET_DSA_MV88E6123_61_65
 	bool "Marvell 88E6123/6161/6165 ethernet switch chip support"
 	select NET_DSA_MV88E6XXX

net/dsa/Makefile

@@ -5,6 +5,7 @@ obj-$(CONFIG_NET_DSA_TAG_EDSA) += tag_edsa.o
 # switch drivers
 obj-$(CONFIG_NET_DSA_MV88E6XXX) += mv88e6xxx.o
 obj-$(CONFIG_NET_DSA_MV88E6123_61_65) += mv88e6123_61_65.o
+obj-$(CONFIG_NET_DSA_MV88E6131) += mv88e6131.o
 
 # the core
 obj-$(CONFIG_NET_DSA) += dsa.o slave.o