debug: enable kernel boot up time measurement

To measure kernel boot up time, reserved region in pl011 is used as trap
MMIO region to record kernel boot timestamp.
For now, we trap at 2 point: the first is nearly the first instruction of
kernel start; the second is just before call the init bin for userspace.
These 2 points can cover the whole kernel boot time.

If there is no pl011, the first write is still there but the second
won't happen.

Signed-off-by: Jianyong Wu <jianyong.wu@arm.com>

Author: jongwu

arch/arm64/kernel/head.S

@@ -86,6 +86,7 @@
 	 *  x28        create_idmap()                           callee preserved temp register
 	 */
 SYM_CODE_START(primary_entry)
+	bl	trap_to_vmm
 	bl	preserve_boot_args
 	bl	init_kernel_el			// w0=cpu_boot_mode
 	mov	x20, x0
@@ -109,6 +110,21 @@ SYM_CODE_START(primary_entry)
 	b	__primary_switch
 SYM_CODE_END(primary_entry)
 
+/*
+ * By writing to mmio region, trap to vmm to print timestamp,
+ * but corrupt x7 and x8.
+ * 0x9000f00 is debug region of pl011
+ * 0x40 is the code specified in cloud hypervisor indicating the first debug
+ * point of kernel.
+ */
+SYM_CODE_START(trap_to_vmm)
+	movz	x7, 0x0900, lsl 16
+	add	x7, x7, 0xf00
+	mov	x8, 0x40
+	str	w8, [x7]
+	ret
+SYM_CODE_END(trap_to_vmm)
+
 /*
  * Preserve the arguments passed by the bootloader in x0 .. x3
  */

drivers/tty/serial/amba-pl011.c

@@ -2730,6 +2730,10 @@ static int pl011_setup_port(struct device *dev, struct uart_amba_port *uap,
 	if (IS_ERR(base))
 		return PTR_ERR(base);
 
+	pl011_debug_addr = (char __iomem *)base;
+	pl011_debug_addr += UART011_IO_DEBUG;
+	has_pl011 = 1;
+
 	index = pl011_probe_dt_alias(index, dev);
 
 	uap->port.dev = dev;

include/linux/amba/serial.h

@@ -206,6 +206,8 @@
 #define UART01x_RSR_ANY		(UART01x_RSR_OE|UART01x_RSR_BE|UART01x_RSR_PE|UART01x_RSR_FE)
 #define UART01x_FR_MODEM_ANY	(UART01x_FR_DCD|UART01x_FR_DSR|UART01x_FR_CTS)
 
+#define UART011_IO_DEBUG	0xf00		/* used for debug I/O port emulation in VM */
+
 #ifndef __ASSEMBLY__
 struct amba_device; /* in uncompress this is included but amba/bus.h is not */
 struct amba_pl010_data {
@@ -225,4 +227,14 @@ struct amba_pl011_data {
 };
 #endif
 
+extern char __iomem *pl011_debug_addr;		/* save the pl011 debug mmio address, equal to base + UART011_IO_DEBUG */
+extern int has_pl011;
+#define DEBUG_TRAP_VAL_END_BOOT 0x41		/* debug point at the end of kernel boot */
+
+/* wrapper of tricking pl011 debug */
+static inline void pl011_debug_trap(char val)
+{
+	writeb_relaxed(val, pl011_debug_addr);
+}
+
 #endif

init/main.c

@@ -102,6 +102,7 @@
 #include <linux/stackdepot.h>
 #include <linux/randomize_kstack.h>
 #include <net/net_namespace.h>
+#include <linux/amba/serial.h>
 
 #include <asm/io.h>
 #include <asm/bugs.h>
@@ -114,6 +115,8 @@
 
 #include <kunit/test.h>
 
+char __iomem *pl011_debug_addr;
+int has_pl011 = 0;
 static int kernel_init(void *);
 
 extern void init_IRQ(void);
@@ -1552,6 +1555,11 @@ static int __ref kernel_init(void *unused)
 	outb(0x41, 0x80);
 #endif
 
+#ifdef CONFIG_ARM64
+	if (has_pl011)
+		pl011_debug_trap(DEBUG_TRAP_VAL_END_BOOT);
+#endif
+
 	if (ramdisk_execute_command) {
 		ret = run_init_process(ramdisk_execute_command);
 		if (!ret)