V4L/DVB (7830): dvb_ca_en50221: Fix High CPU load in 'top' due to budget_av slot polling

This change addresses kernel bug #10459: In kernel 2.6.25 the
budget_av driver polls for an CI slot in 100ms intervals (because no
interrupt solution for budget_av cards is feasible due to HW reasons).
If no CI/CAM is connected to the DVB card, polling times out only after 250ms.
This periodic polling leads to high CPU load.

The change increases the polling interval for empty slots from 100ms to 5s.
Intervals for remaining slot states (invalid, in progress, ready) are unchanged,
as they are either temporary conditions or no timeout should occur.
Signed-off-by: NRobert Schedel <r.schedel@yahoo.de>
Signed-off-by: NOliver Endriss <o.endriss@gmx.de>
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/dvb/dvb-core/dvb_ca_en50221.c

@@ -910,15 +910,21 @@ static void dvb_ca_en50221_thread_update_delay(struct dvb_ca_private *ca)
 	int curdelay = 100000000;
 	int slot;
 
+	/* Beware of too high polling frequency, because one polling
+	 * call might take several hundred milliseconds until timeout!
+	 */
 	for (slot = 0; slot < ca->slot_count; slot++) {
 		switch (ca->slot_info[slot].slot_state) {
 		default:
 		case DVB_CA_SLOTSTATE_NONE:
+			delay = HZ * 60;  /* 60s */
+			if (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_CAMCHANGE))
+				delay = HZ * 5;  /* 5s */
+			break;
 		case DVB_CA_SLOTSTATE_INVALID:
-			delay = HZ * 60;
-			if (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_CAMCHANGE)) {
-				delay = HZ / 10;
-			}
+			delay = HZ * 60;  /* 60s */
+			if (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_CAMCHANGE))
+				delay = HZ / 10;  /* 100ms */
 			break;
 
 		case DVB_CA_SLOTSTATE_UNINITIALISED:
@@ -926,19 +932,17 @@ static void dvb_ca_en50221_thread_update_delay(struct dvb_ca_private *ca)
 		case DVB_CA_SLOTSTATE_VALIDATE:
 		case DVB_CA_SLOTSTATE_WAITFR:
 		case DVB_CA_SLOTSTATE_LINKINIT:
-			delay = HZ / 10;
+			delay = HZ / 10;  /* 100ms */
 			break;
 
 		case DVB_CA_SLOTSTATE_RUNNING:
-			delay = HZ * 60;
-			if (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_CAMCHANGE)) {
-				delay = HZ / 10;
-			}
+			delay = HZ * 60;  /* 60s */
+			if (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_CAMCHANGE))
+				delay = HZ / 10;  /* 100ms */
 			if (ca->open) {
 				if ((!ca->slot_info[slot].da_irq_supported) ||
-				    (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_DA))) {
-					delay = HZ / 10;
-				}
+				    (!(ca->flags & DVB_CA_EN50221_FLAG_IRQ_DA)))
+					delay = HZ / 10;  /* 100ms */
 			}
 			break;
 		}