Fix for dispc's error "omapfb omapfb: irq error status 4020"

[Rick Bronson <rick@efn.org>]

Folks,

  Please take a look at this change to drivers/video/omap/dispc.c.  It
addresses a problem seen on some boots of OMAP's.  On about 1 in 30
boots one gets an endless stream of interrupts from the
DISPC_IRQ_SYNC_LOST bit in the DISPC_IRQSTATUS register.  The
following messages are printed.

 omapfb omapfb: irq error status 4020

  The correct solution to this problem is to perform a "soft reset"
but that requires a bit of re-architecturing of the code as the init
routine would have to be split up, etc.  See the OMAP pdf, search for
"To clear a synchronization lost interrupt".

  This patch allows the above error message to get printed once and
then disables further DISPC_IRQ_SYNC_LOST interrups.

  Comments?

  Thanks,

 Rick

--- linux-omap-2.6/drivers/video/omap/dispc.c.~1~	2008-11-04 14:23:38.000000000 -0800
+++ linux-omap-2.6/drivers/video/omap/dispc.c	2008-11-07 12:34:54.000000000 -0800
@@ -157,7 +157,7 @@ struct resmap {
 
 #define MAX_IRQ_HANDLERS            4
 
-static struct {
+static struct omapfb_dispc {
 	void __iomem	*base;
 
 	struct omapfb_mem_desc	mem_desc;
@@ -169,6 +169,7 @@ static struct {
 
 	int		ext_mode;
 
+	u32	irq_error_mask;  /* mask used for errors */
 	struct {
 		u32	irq_mask;
 		void	(*callback)(void *);
@@ -812,16 +813,16 @@ static void set_lcd_timings(void)
 	panel->pixel_clock = fck / lck_div / pck_div / 1000;
 }
 
-static void recalc_irq_mask(void)
+static void recalc_irq_mask(struct omapfb_dispc *p_dispc)
 {
 	int i;
-	unsigned long irq_mask = DISPC_IRQ_MASK_ERROR;
+	unsigned long irq_mask = p_dispc->irq_error_mask;
 
 	for (i = 0; i < MAX_IRQ_HANDLERS; i++) {
-		if (!dispc.irq_handlers[i].callback)
+		if (!p_dispc->irq_handlers[i].callback)
 			continue;
 
-		irq_mask |= dispc.irq_handlers[i].irq_mask;
+		irq_mask |= p_dispc->irq_handlers[i].irq_mask;
 	}
 
 	enable_lcd_clocks(1);
@@ -843,7 +844,7 @@ int omap_dispc_request_irq(unsigned long
 		dispc.irq_handlers[i].irq_mask = irq_mask;
 		dispc.irq_handlers[i].callback = callback;
 		dispc.irq_handlers[i].data = data;
-		recalc_irq_mask();
+		recalc_irq_mask(&dispc);
 
 		return 0;
 	}
@@ -863,7 +864,7 @@ void omap_dispc_free_irq(unsigned long i
 			dispc.irq_handlers[i].irq_mask = 0;
 			dispc.irq_handlers[i].callback = NULL;
 			dispc.irq_handlers[i].data = NULL;
-			recalc_irq_mask();
+			recalc_irq_mask(&dispc);
 			return;
 		}
 	}
@@ -884,6 +885,10 @@ static irqreturn_t omap_dispc_irq_handle
 		complete(&dispc.frame_done);
 
 	if (stat & DISPC_IRQ_MASK_ERROR) {
+		if (stat & DISPC_IRQ_SYNC_LOST) {  /* only allow sync lost once or we end up... */
+			dispc.irq_error_mask &= ~DISPC_IRQ_SYNC_LOST;  /* with a barrage of interrupts */
+			recalc_irq_mask(&dispc);
+			}
 		if (printk_ratelimit()) {
 			dev_err(dispc.fbdev->dev, "irq error status %04x\n",
 				stat & 0x7fff);
@@ -897,6 +902,7 @@ static irqreturn_t omap_dispc_irq_handle
 	}
 
 	dispc_write_reg(DISPC_IRQSTATUS, stat);
+	stat = dispc_read_reg(DISPC_IRQSTATUS);
 
 	enable_lcd_clocks(0);
 
@@ -1432,7 +1438,8 @@ static int omap_dispc_init(struct omapfb
 	l = dispc_read_reg(DISPC_IRQSTATUS);
 	dispc_write_reg(DISPC_IRQSTATUS, l);
 
-	recalc_irq_mask();
+	dispc.irq_error_mask = DISPC_IRQ_MASK_ERROR;  /* init error mask */
+	recalc_irq_mask(&dispc);
 
 	if ((r = request_irq(INT_24XX_DSS_IRQ, omap_dispc_irq_handler,
 			   0, MODULE_NAME, fbdev)) < 0) {