Improve early kernel debugging prints

Since the early kernel debugging prints are useful only in a few
debugging scenarios, define a configuration option that disables them by
default (if enabled, it produces duplicate output which might be
confusing).

Implement early kernel debugging prints for the HiKey960.

HelenOS.config

@@ -395,6 +395,9 @@
 % Debug build
 ! CONFIG_DEBUG (y/n)
 
+% Early debugging print
+! [CONFIG_DEBUG=y] CONFIG_DEBUG_EARLY_PRINT (n/y)
+
 % Sanitize undefined behavior (userspace)
 ! CONFIG_UBSAN (n/y)
 

kernel/arch/amd64/src/asm.S

@@ -410,6 +410,8 @@ bad_rip_msg:
  */
 FUNCTION_BEGIN(early_putuchar)
 
+#if (defined(CONFIG_DEBUG_EARLY_PRINT))
+
 #if (defined(CONFIG_L4RE_UVMM_EARLY_PRINT))
 	xorl %eax, %eax  /* RAX==0: uvmm's print hypercall */
 	mov %rdi, %rcx   /* RCX:    printed character */
@@ -540,6 +542,8 @@ FUNCTION_BEGIN(early_putuchar)
 	popq %rbx
 	leave
 
+#endif
+
 #endif
 
 	ret

kernel/arch/arm64/include/arch/machine_func.h

@@ -49,6 +49,7 @@ struct arm_machine_ops {
 	inr_t (*machine_enable_vtimer_irq)(void);
 	size_t (*machine_get_irq_count)(void);
 	const char *(*machine_get_platform_name)(void);
+	void (*machine_early_uart_output)(char32_t);
 };
 
 extern void machine_ops_init(void);
@@ -59,6 +60,7 @@ extern void machine_input_init(void);
 extern inr_t machine_enable_vtimer_irq(void);
 extern size_t machine_get_irq_count(void);
 extern const char *machine_get_platform_name(void);
+extern void machine_early_uart_output(char32_t);
 
 #endif
 

kernel/arch/arm64/src/arm64.c

@@ -39,6 +39,7 @@
 #include <arch/asm.h>
 #include <arch/exception.h>
 #include <arch/machine_func.h>
+#include <console/console.h>
 #include <interrupt.h>
 #include <proc/scheduler.h>
 #include <syscall/syscall.h>
@@ -255,5 +256,15 @@ void irq_initialize_arch(irq_t *irq __attribute__((unused)))
 {
 }
 
+void early_putuchar(char32_t c)
+{
+#ifdef CONFIG_DEBUG_EARLY_PRINT
+	if (c == '\n')
+		machine_early_uart_output('\r');
+
+	machine_early_uart_output(c);
+#endif
+}
+
 /** @}
  */

kernel/arch/arm64/src/asm.S

@@ -55,10 +55,6 @@ FUNCTION_BEGIN(memcpy_to_uspace_failover_address)
 FUNCTION_END(memcpy_from_uspace_failover_address)
 FUNCTION_END(memcpy_to_uspace_failover_address)
 
-FUNCTION_BEGIN(early_putuchar)
-	ret
-FUNCTION_END(early_putuchar)
-
 /** Flush instruction caches
  *
  * @param x0 Starting address of the flushing.

kernel/arch/arm64/src/mach/hikey960/hikey960.c

@@ -121,14 +121,28 @@ static const char *hikey960_get_platform_name(void)
 	return "hikey960";
 }
 
+static void hikey960_early_uart_output(char32_t c)
+{
+	volatile uint32_t *uartdr = (volatile uint32_t *)
+	    PA2KA(HIKEY960_UART_ADDRESS);
+	volatile uint32_t *uartfr = (volatile uint32_t *)
+	    PA2KA(HIKEY960_UART_ADDRESS + 24);
+
+	while (*uartfr & 0x20U) {
+	}
+
+	*uartdr = c;
+}
+
 struct arm_machine_ops hikey960_machine_ops = {
 	hikey960_init,
 	hikey960_irq_exception,
 	hikey960_output_init,
 	hikey960_input_init,
 	hikey960_enable_vtimer_irq,
 	hikey960_get_irq_count,
-	hikey960_get_platform_name
+	hikey960_get_platform_name,
+	hikey960_early_uart_output
 };
 
 /** @}

kernel/arch/arm64/src/machine_func.c

@@ -100,5 +100,12 @@ const char *machine_get_platform_name(void)
 	return machine_ops->machine_get_platform_name();
 }
 
+/** Early debugging output. */
+void machine_early_uart_output(char32_t c)
+{
+	if (machine_ops->machine_early_uart_output != NULL)
+		machine_ops->machine_early_uart_output(c);
+}
+
 /** @}
  */

kernel/arch/ia32/src/asm.S

@@ -452,7 +452,7 @@ interrupt_handlers:
  */
 FUNCTION_BEGIN(early_putuchar)
 
-#if ((defined(CONFIG_EGA)) && (!defined(CONFIG_FB)))
+#if ((defined(CONFIG_DEBUG_EARLY_PRINT)) && (defined(CONFIG_EGA)) && (!defined(CONFIG_FB)))
 
 	/* Prologue, save preserved registers */
 	pushl %ebp

kernel/generic/src/console/console.c

@@ -378,7 +378,7 @@ void putuchar(const char32_t ch)
 		 *
 		 * The early_putuchar() function is used to output
 		 * the character for low-level debugging purposes.
-		 * Note that the early_putc() function might be
+		 * Note that the early_putuchar() function might be
 		 * a no-op on certain hardware configurations.
 		 */
 		early_putuchar(ch);