[linux-dvb] [PATCH] fix for stream corruption on budget / Nova-T cards

[Jon Burgess <mplayer@jburgess.uklinux.net>]

Here is a patch which completely fixes all the stream distortion 
problems i've been seeing on my P4 system. This works without needing to 
apply any of the proposed PCI tweaks.

After many hours of debugging last night, it looks like the corruption 
is caused by a hardware bug in the DMA engine used in the SAA7146. See 
the patch for more info.

A similar problem might effect the other DMA engines used by the full 
featured cards, but I don't have one to experiment with.

	Jon


--- cvs/dvb-kernel/linux/drivers/media/dvb/ttpci/budget-core.c	2003-06-26 18:42:36.000000000 +0100
+++ dvb-kernel/linux/drivers/media/dvb/ttpci/budget-core.c	2003-08-30 03:15:44.000000000 +0100
@@ -68,6 +68,18 @@
         u32 olddma = budget->ttbp;
         u32 newdma = saa7146_read(budget->dev, PCI_VDP3);
 
+	if ((newdma == 0) || (newdma == TS_BUFLEN / 2)) {
+	          /* The DMA Pointer is unreliable at 0% and 50% of buffer and
+	           * frequently gets the two positions confused, we make a
+		   * guess of the likely value based on the last known value
+		   */
+	           if (olddma < TS_BUFLEN/2) {
+		           newdma = TS_BUFLEN/2;
+		   } else {
+		           newdma = 0;
+		   }
+	}
+
         /* nearest lower position divisible by 188 */
         newdma -= newdma % 188;