FROMLIST: PCI: pwrctrl: Add power control driver for tc9563

TC9563 is a PCIe switch which has one upstream and three downstream
ports. To one of the downstream ports ethernet MAC is connected as endpoint
device. Other two downstream ports are supposed to connect to external
device. One Host can connect to TC9563 by upstream port. TC9563 switch
needs to be configured after powering on and before PCIe link was up.

The PCIe controller driver already enables link training at the host side
even before this driver probe happens, due to this when driver enables
power to the switch it participates in the link training and PCIe link
may come up before configuring the switch through i2c. Once the link is
up the configuration done through i2c will not have any affect.To prevent
the host from participating in link training, disable link training on the
host side to ensure the link does not come up before the switch is
configured via I2C.

Based up on dt property and type of the port, tc9563 is configured
through i2c.

Link: https://lore.kernel.org/lkml/[email protected]/
Signed-off-by: Krishna Chaitanya Chundru <[email protected]>
Reviewed-by: Bjorn Andersson <[email protected]>
Reviewed-by: Bartosz Golaszewski <[email protected]>

Author: krishnachaitanya-linux

drivers/pci/pwrctrl/Kconfig

@@ -31,3 +31,13 @@ config HAVE_PWRCTL
 config PCI_PWRCTL_PWRSEQ
 	tristate
 	select PCI_PWRCTRL_PWRSEQ
+
+config PCI_PWRCTRL_TC9563
+	tristate "PCI Power Control driver for TC9563 PCIe switch"
+	select PCI_PWRCTRL
+	help
+	  Say Y here to enable the PCI Power Control driver of TC9563 PCIe
+	  switch.
+
+	  This driver enables power and configures the TC9563 PCIe switch
+	  through i2c.

drivers/pci/pwrctrl/Makefile

@@ -7,3 +7,5 @@ obj-$(CONFIG_PCI_PWRCTRL_PWRSEQ)	+= pci-pwrctrl-pwrseq.o
 
 obj-$(CONFIG_PCI_PWRCTRL_SLOT)		+= pci-pwrctrl-slot.o
 pci-pwrctrl-slot-y			:= slot.o
+
+obj-$(CONFIG_PCI_PWRCTRL_TC9563)	+= pci-pwrctrl-tc9563.o