PCI: pwrctrl: Add power control driver for TC9563

TC9563 is a PCIe switch that has one upstream and three downstream ports.
One of the downstream ports is connected to an integrated ethernet MAC
endpoint. The other two downstream ports are available to connect to
external devices. One Host can connect to TC9563 by upstream port. The
TC9563 switch needs to be configured after powering on and before the PCIe
link is 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 link training and the 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 effect. 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 on DT property and type of the port, TC9563 is configured through
I2C.

Signed-off-by: Krishna Chaitanya Chundru <krishna.chundru@oss.qualcomm.com>
[bhelgaas: squash fixes from
https://lore.kernel.org/r/20251120065116.13647-2-mani@kernel.org
https://lore.kernel.org/r/20251120065116.13647-3-mani@kernel.org]
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Bjorn Andersson <andersson@kernel.org>
Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Link: https://patch.msgid.link/20251101-tc9563-v9-6-de3429f7787a@oss.qualcomm.com

Author: krishnachaitanya-linux

drivers/pci/pwrctrl/Kconfig

@@ -22,6 +22,21 @@ config PCI_PWRCTRL_SLOT
 	  PCI slots. The voltage regulators powering the rails of the PCI slots
 	  are expected to be defined in the devicetree node of the PCI bridge.
 
+config PCI_PWRCTRL_TC9563
+	tristate "PCI Power Control driver for TC9563 PCIe switch"
+	select PCI_PWRCTRL
+	default m if ARCH_QCOM
+	depends on I2C
+	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. TC9563 is a PCIe switch which has one upstream and three
+	  downstream ports. To one of the downstream ports integrated ethernet
+	  MAC is connected as endpoint device. Other two downstream ports are
+	  supposed to connect to external device.
+
 # deprecated
 config HAVE_PWRCTL
 	bool

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