vt: add cursor blink interval escape sequence

Add an escape sequence to specify the current console's cursor blink
interval. The interval is specified as a number of milliseconds until
the next cursor display state toggle, from 50 to 65535. /proc/loadavg
did not show a difference with a one msec interval, but the lower
bound is set to 50 msecs since slower hardware wasn't tested.

Store the interval in the vc_data structure for later access by fbcon,
initializing the value to fbcon's current hardcoded value of 200 msecs.
Signed-off-by: Scot Doyle <lkml14@scotdoyle.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/vt/vt.c

@@ -135,6 +135,7 @@ const struct consw *conswitchp;
  */
 #define DEFAULT_BELL_PITCH	750
 #define DEFAULT_BELL_DURATION	(HZ/8)
+#define DEFAULT_CURSOR_BLINK_MS	200
 
 struct vc vc_cons [MAX_NR_CONSOLES];
 
@@ -1590,6 +1591,13 @@ static void setterm_command(struct vc_data *vc)
 		case 15: /* activate the previous console */
 			set_console(last_console);
 			break;
+		case 16: /* set cursor blink duration in msec */
+			if (vc->vc_npar >= 1 && vc->vc_par[1] >= 50 &&
+					vc->vc_par[1] <= USHRT_MAX)
+				vc->vc_cur_blink_ms = vc->vc_par[1];
+			else
+				vc->vc_cur_blink_ms = DEFAULT_CURSOR_BLINK_MS;
+			break;
 	}
 }
 
@@ -1717,6 +1725,7 @@ static void reset_terminal(struct vc_data *vc, int do_clear)
 
 	vc->vc_bell_pitch = DEFAULT_BELL_PITCH;
 	vc->vc_bell_duration = DEFAULT_BELL_DURATION;
+	vc->vc_cur_blink_ms = DEFAULT_CURSOR_BLINK_MS;
 
 	gotoxy(vc, 0, 0);
 	save_cur(vc);

include/linux/console_struct.h

@@ -104,6 +104,7 @@ struct vc_data {
 	unsigned int    vc_resize_user;         /* resize request from user */
 	unsigned int	vc_bell_pitch;		/* Console bell pitch */
 	unsigned int	vc_bell_duration;	/* Console bell duration */
+	unsigned short	vc_cur_blink_ms;	/* Cursor blink duration */
 	struct vc_data **vc_display_fg;		/* [!] Ptr to var holding fg console for this display */
 	struct uni_pagedir *vc_uni_pagedir;
 	struct uni_pagedir **vc_uni_pagedir_loc; /* [!] Location of uni_pagedir variable for this console */