diff -r e880629062dd -r e4a7b1cbe40c kernel/eka/include/drivers/dma_v2.h
--- a/kernel/eka/include/drivers/dma_v2.h	Wed May 05 05:11:16 2010 +0100
+++ b/kernel/eka/include/drivers/dma_v2.h	Mon May 10 11:40:53 2010 +0100
@@ -1197,14 +1197,53 @@
 		empty request queue, or immediately after the request count has become
 		zero because of request cancellation or completion.
 
-		Depending on the current value of iQueuedRequests, the PSL may power
-		down or power up the channel. Note that iQueuedRequests gets accessed
-		and changed by different threads, so the PSL needs to take the usual
-		precautions when evaluating the variable's value.
+		Depending on the current and previous observed values of
+		iQueuedRequests, the PSL may power down or power up the channel.
+
+		Note that iQueuedRequests gets accessed and changed by different
+		threads, so the PSL needs to take the usual precautions when evaluating
+		the variable's value. Also, due to the multithreaded framework
+		architecture, there is no guarantee that the function calls always
+		arrive at the PSL level in the strict chronological order of
+		iQueuedRequests being incremented/decremented in the PIL, i.e. it might
+		happen that the PSL finds iQueuedRequests to have the same value in two
+		or more consecutive calls (that's why the previous observed value needs
+		to be locally available and taken into account). It is however promised
+		that before any actual transfer commences the PSL will find the request
+		count to be greater than zero and that after the last request has
+		finished it will be found to be zero.
 
 		None of the internal DMA framework mutexes is being held by the PIL
 		when calling this function.
 
+		Here is an example implementation for a derived channel class:
+
+		@code
+
+		class TFooDmaChannel : public TDmaSgChannel
+			{
+			DMutex* iDmaMutex;
+			TInt iPrevQueuedRequests;
+			virtual void QueuedRequestCountChanged();
+			};
+
+		void TFooDmaChannel::QueuedRequestCountChanged()
+			{
+			Kern::MutexWait(*iDmaMutex);
+			if ((iQueuedRequests > 0) && (iPrevQueuedRequests == 0))
+				{
+				IncreasePowerCount(); // Base port specific
+				}
+			else if ((iQueuedRequests == 0) && (iPrevQueuedRequests > 0))
+				{
+				DecreasePowerCount(); // Base port specific
+				}
+			iPrevQueuedRequests = iQueuedRequests;
+			Kern::MutexSignal(*iDmaMutex);
+			}
+
+		@endcode
+
 		@see iQueuedRequests
 	*/
 	virtual void QueuedRequestCountChanged();