2.4.0-test13-pre2: better parport_pc commentary

@@ -938,13 +938,11 @@
 			/* Can't yield the port. */
 			schedule ();
 
-		/* At this point, the FIFO may already be full.
-		 * Ideally, we'd be able to tell the port to hold on
-		 * for a second while we empty the FIFO, and we'd be
-		 * able to ensure that no data is lost.  I'm not sure
-		 * that's the case. :-(  It might be that you can play
-		 * games with STB, as in the forward case; someone should
-		 * look at a datasheet. */
+		/* At this point, the FIFO may already be full. In
+                 * that case ECP is already holding back the
+                 * peripheral (assuming proper design) with a delayed
+                 * handshake.  Work fast to avoid a peripheral
+                 * timeout.  */
 
 		if (ecrval & 0x01) {
 			/* FIFO is empty. Wait for interrupt. */

@@ -976,6 +974,10 @@
 				goto false_alarm;
 			}
 
+			/* Depending on how the FIFO threshold was
+                         * set, how long interrupt service took, and
+                         * how fast the peripheral is, we might be
+                         * lucky and have a just filled FIFO. */
 			continue;
 		}
 

@@ -987,6 +989,9 @@
 			continue;
 		}
 
+		/* FIFO not filled.  We will cycle this loop for a while
+                 * and either the peripheral will fill it faster,
+                 * tripping a fast empty with insb, or we empty it. */
 		*bufp++ = inb (fifo);
 		left--;
 	}