ubb-vga: new option -2 to keep on refreshing the LCD display (experimental)

"Experimental" means that it doesn't seem to work at the moment.

- regs4740.h (_LCD, LCDCTRL): added the LCD control register
- ubb-vga.c (old_lcdctrl, tame_lcd, restore_lcd): make the LCD controller
  use short bursts, to reduce the bus access latency for other users
- ubb-vga.c (keep_lcd, setup_noirq, cleanup_noirq, usage, main): new
  option -2 to keep on refreshing the LCD display

ubb-vga/regs4740.h

@@ -30,6 +30,7 @@
 #define	_GPIO(n)	REG(0x0010000+(n))
 #define	_MSC(n)		REG(0x0021000+(n))
 #define	_DMAC(n)	REG(0x3020000+(n))
+#define	_LCD(n)		REG(0x3050000+(n))
 
 #define	CLKGR	_CGU(0x0020)	/* Clock Gate */
 #define	MSCCDR	_CGU(0x0068)	/* MSC device clock divider */
@@ -80,4 +81,6 @@
 #define	DMAC		_DMAC(0x300)	/* DMA control */
 #define	DDR		_DMAC(0x308)	/* DMA doorbell */
 
+#define	LCDCTRL		_LCD(0x30)	/* LCD control */
+
 #endif /* !REGS4740_H */

ubb-vga/ubb-vga.c

@@ -43,6 +43,7 @@
 static volatile void *base;
 
 static int bad;
+static int keep_lcd = 0;
 
 
 #define	US(us)	((uint16_t) ((us)*112))
@@ -141,6 +142,7 @@ static uint32_t clkrt = 0;
 
 static uint32_t old_icmr;
 static uint32_t old_clkgr;
+static uint32_t old_lcdctrl;
 
 
 static void disable_interrupts(void)
@@ -181,6 +183,20 @@ static void enable_lcd(void)
 }
 
 
+static void tame_lcd(void)
+{
+	old_lcdctrl = LCDCTRL;
+	/* LCDCTRL.BST = 0, for 4 word burst, the shortest available */
+	LCDCTRL = old_lcdctrl & 0xfffffff;
+}
+
+
+static void restore_lcd(void)
+{
+	LCDCTRL = old_lcdctrl;
+}
+
+
 static void get_timer(void)
 {
 	TSCR = 1 << TIMER;	/* enable clock */
@@ -269,6 +285,9 @@ static void setup(void)
 
 static void setup_noirq(void)
 {
+	if (keep_lcd)
+		tame_lcd();
+	else
 		disable_lcd();
 	get_timer();
 
@@ -290,6 +309,9 @@ static void cleanup_noirq(void)
 	DCS(DMA) = 0;
 
 	release_timer();
+	if (keep_lcd)
+		restore_lcd();
+	else
 		enable_lcd();
 }
 
@@ -448,10 +470,11 @@ static void list_modes(void)
 static void usage(const char *name)
 {
 	fprintf(stderr,
-"usage: %s [-t] [-r resolution] [frames [file]]\n"
+"usage: %s [-2] [-t] [-r resolution] [frames [file]]\n"
 "       %s -l\n\n"
 "  frames  number of frames to display\n"
 "  file    PPM file\n\n"
+"  -2       keep on refreshing the LCD display (experimental)\n"
 "  -l       list available modes\n"
 "  -m mode  select the display mode, default \"%s\"\n"
 "  -t       generate a test image\n"
@@ -466,8 +489,11 @@ int main(int argc, char *const *argv)
 	int frames = 0;
 	int c;
 
-	while ((c = getopt(argc, argv, "lm:t")) != EOF)
+	while ((c = getopt(argc, argv, "2lm:t")) != EOF)
 		switch (c) {
+		case '2':
+			keep_lcd = 1;
+			break;
 		case 'l':
 			list_modes();
 			exit(0);