timer: cadence: Implement timer_get_boot_us

This function is required for adding bootstage support.
Also enable it directly for ZynqMP R5 configuration.

Signed-off-by: Michal Simek <michal.simek@xilinx.com>

configs/xilinx_zynqmp_r5_defconfig

@@ -5,10 +5,12 @@ CONFIG_DEBUG_UART_BASE=0xff010000
 CONFIG_DEBUG_UART_CLOCK=100000000
 CONFIG_DEFAULT_DEVICE_TREE="zynqmp-r5"
 CONFIG_DEBUG_UART=y
+CONFIG_BOOTSTAGE=y
 # CONFIG_DISPLAY_CPUINFO is not set
 CONFIG_SYS_PROMPT="ZynqMP r5> "
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_SETEXPR is not set
+CONFIG_CMD_BOOTSTAGE=y
 CONFIG_OF_EMBED=y
 CONFIG_DEBUG_UART_ZYNQ=y
 CONFIG_ZYNQ_SERIAL=y

drivers/timer/cadence-ttc.c

@@ -31,6 +31,28 @@ struct cadence_ttc_priv {
 	struct cadence_ttc_regs *regs;
 };
 
+#if CONFIG_IS_ENABLED(BOOTSTAGE)
+ulong timer_get_boot_us(void)
+{
+	u64 ticks = 0;
+	u32 rate = 1;
+	u64 us;
+	int ret;
+
+	ret = dm_timer_init();
+	if (!ret) {
+		/* The timer is available */
+		rate = timer_get_rate(gd->timer);
+		timer_get_count(gd->timer, &ticks);
+	} else {
+		return 0;
+	}
+
+	us = (ticks * 1000) / rate;
+	return us;
+}
+#endif
+
 static int cadence_ttc_get_count(struct udevice *dev, u64 *count)
 {
 	struct cadence_ttc_priv *priv = dev_get_priv(dev);