console: Implement flush() function

On certain places it is required to flush output print buffers to ensure
that text strings were sent to console or serial devices. For example when
printing message that U-Boot is going to boot kernel or when U-Boot is
going to change baudrate of terminal device.

Therefore introduce a new flush() and fflush() functions into console code.
These functions will call .flush callback of associated stdio_dev device.

As this function may increase U-Boot side, allow to compile U-Boot without
this function. For this purpose there is a new config CONSOLE_FLUSH_SUPPORT
which is enabled by default and can be disabled. It is a good idea to have
this option enabled for all boards which have enough space for it.

When option is disabled when U-Boot defines just empty static inline
function fflush() to avoid ifdefs in other code.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>

common/Kconfig

@@ -186,6 +186,12 @@ config PRE_CON_BUF_ADDR
 	  We should consider removing this option and allocating the memory
 	  in board_init_f_init_reserve() instead.
 
+config CONSOLE_FLUSH_SUPPORT
+	bool "Enable console flush support"
+	default y
+	help
+	  This enables compilation of flush() function for console flush support.
+
 config CONSOLE_MUX
 	bool "Enable console multiplexing"
 	default y if DM_VIDEO || VIDEO || LCD

common/console.c

@@ -199,6 +199,7 @@ static int console_setfile(int file, struct stdio_dev * dev)
 		case stdout:
 			gd->jt->putc  = putc;
 			gd->jt->puts  = puts;
+			STDIO_DEV_ASSIGN_FLUSH(gd->jt, flush);
 			gd->jt->printf = printf;
 			break;
 		}
@@ -364,6 +365,19 @@ static void console_puts(int file, const char *s)
 	}
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+static void console_flush(int file)
+{
+	int i;
+	struct stdio_dev *dev;
+
+	for_each_console_dev(i, file, dev) {
+		if (dev->flush != NULL)
+			dev->flush(dev);
+	}
+}
+#endif
+
 #if CONFIG_IS_ENABLED(SYS_CONSOLE_IS_IN_ENV)
 static inline void console_doenv(int file, struct stdio_dev *dev)
 {
@@ -413,6 +427,14 @@ static inline void console_puts(int file, const char *s)
 	stdio_devices[file]->puts(stdio_devices[file], s);
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+static inline void console_flush(int file)
+{
+	if (stdio_devices[file]->flush)
+		stdio_devices[file]->flush(stdio_devices[file]);
+}
+#endif
+
 #if CONFIG_IS_ENABLED(SYS_CONSOLE_IS_IN_ENV)
 static inline void console_doenv(int file, struct stdio_dev *dev)
 {
@@ -526,6 +548,14 @@ void fputs(int file, const char *s)
 		console_puts(file, s);
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+void fflush(int file)
+{
+	if (file < MAX_FILES)
+		console_flush(file);
+}
+#endif
+
 int fprintf(int file, const char *fmt, ...)
 {
 	va_list args;
@@ -740,6 +770,37 @@ void puts(const char *s)
 	}
 }
 
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+void flush(void)
+{
+	if (!gd)
+		return;
+
+	/* sandbox can send characters to stdout before it has a console */
+	if (IS_ENABLED(CONFIG_SANDBOX) && !(gd->flags & GD_FLG_SERIAL_READY)) {
+		os_flush();
+		return;
+	}
+
+	if (IS_ENABLED(CONFIG_DEBUG_UART) && !(gd->flags & GD_FLG_SERIAL_READY))
+		return;
+
+	if (IS_ENABLED(CONFIG_SILENT_CONSOLE) && (gd->flags & GD_FLG_SILENT))
+		return;
+
+	if (IS_ENABLED(CONFIG_DISABLE_CONSOLE) && (gd->flags & GD_FLG_DISABLE_CONSOLE))
+		return;
+
+	if (!gd->have_console)
+		return;
+
+	if (gd->flags & GD_FLG_DEVINIT) {
+		/* Send to the standard output */
+		fflush(stdout);
+	}
+}
+#endif
+
 #ifdef CONFIG_CONSOLE_RECORD
 int console_record_init(void)
 {

include/_exports.h

@@ -12,6 +12,9 @@
 	EXPORT_FUNC(tstc, int, tstc, void)
 	EXPORT_FUNC(putc, void, putc, const char)
 	EXPORT_FUNC(puts, void, puts, const char *)
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+	EXPORT_FUNC(flush, void, flush, void)
+#endif
 	EXPORT_FUNC(printf, int, printf, const char*, ...)
 #if (defined(CONFIG_X86) && !defined(CONFIG_X86_64)) || defined(CONFIG_PPC)
 	EXPORT_FUNC(irq_install_handler, void, install_hdlr,

include/stdio.h

@@ -15,6 +15,11 @@ int tstc(void);
 		defined(CONFIG_SPL_SERIAL))
 void putc(const char c);
 void puts(const char *s);
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+void flush(void);
+#else
+static inline void flush(void) {}
+#endif
 int __printf(1, 2) printf(const char *fmt, ...);
 int vprintf(const char *fmt, va_list args);
 #else
@@ -26,6 +31,10 @@ static inline void puts(const char *s)
 {
 }
 
+static inline void flush(void)
+{
+}
+
 static inline int __printf(1, 2) printf(const char *fmt, ...)
 {
 	return 0;
@@ -48,11 +57,17 @@ static inline int vprintf(const char *fmt, va_list args)
 /* stderr */
 #define eputc(c)		fputc(stderr, c)
 #define eputs(s)		fputs(stderr, s)
+#define eflush()		fflush(stderr)
 #define eprintf(fmt, args...)	fprintf(stderr, fmt, ##args)
 
 int __printf(2, 3) fprintf(int file, const char *fmt, ...);
 void fputs(int file, const char *s);
 void fputc(int file, const char c);
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+void fflush(int file);
+#else
+static inline void fflush(int file) {}
+#endif
 int ftstc(int file);
 int fgetc(int file);
 

include/stdio_dev.h

@@ -37,6 +37,13 @@ struct stdio_dev {
 	void (*putc)(struct stdio_dev *dev, const char c);
 	/* To put a string (accelerator) */
 	void (*puts)(struct stdio_dev *dev, const char *s);
+#ifdef CONFIG_CONSOLE_FLUSH_SUPPORT
+	/* To flush output queue */
+	void (*flush)(struct stdio_dev *dev);
+#define STDIO_DEV_ASSIGN_FLUSH(dev, flush_func) ((dev)->flush = (flush_func))
+#else
+#define STDIO_DEV_ASSIGN_FLUSH(dev, flush_func)
+#endif
 
 /* INPUT functions */