bus: ti: am33xx: add pwm subsystem driver

The TI PWMSS driver is a simple bus driver for providing clock and power
management for the PWM peripherals on TI AM33xx SoCs, namely eCAP,
eHRPWM and eQEP.

For DT binding details see Linux doc:
- Documentation/devicetree/bindings/pwm/pwm-tipwmss.txt

Signed-off-by: Dario Binacchi <dariobin@libero.it>

drivers/bus/Kconfig

@@ -5,6 +5,12 @@
 
 menu "Bus devices"
 
+config TI_PWMSS
+	bool
+	default y if ARCH_OMAP2PLUS && PWM_TI_EHRPWM
+	help
+	  PWM Subsystem driver support for AM33xx SOC.
+
 config TI_SYSC
 	bool "TI sysc interconnect target module driver"
 	depends on ARCH_OMAP2PLUS

drivers/bus/Makefile

@@ -3,5 +3,6 @@
 # Makefile for the bus drivers.
 #
 
+obj-$(CONFIG_TI_PWMSS)	+= ti-pwmss.o
 obj-$(CONFIG_TI_SYSC)	+= ti-sysc.o
 obj-$(CONFIG_UNIPHIER_SYSTEM_BUS) += uniphier-system-bus.o

drivers/bus/ti-pwmss.c

@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Pulse-Width Modulation Subsystem (pwmss)
+ *
+ * Copyright (C) 2020 Dario Binacchi <dariobin@libero.it>
+ */
+
+#include <common.h>
+#include <dm.h>
+
+static const struct udevice_id ti_pwmss_ids[] = {
+	{.compatible = "ti,am33xx-pwmss"},
+	{}
+};
+
+U_BOOT_DRIVER(ti_pwmss) = {
+	.name = "ti_pwmss",
+	.id = UCLASS_SIMPLE_BUS,
+	.of_match = ti_pwmss_ids,
+	.bind = dm_scan_fdt_dev,
+};