powerpc/spufs: sputrace: Don't block until the read buffer is full

Currently, read() on the sputrace buffer will only return data when
the user buffer is exhausted. This may mean that we never see the
end of the event log, unless we read() with exactly the right-sized
buffer.

This change makes sputrace_read not block if we have data ready to
return.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>

arch/powerpc/platforms/cell/spufs/sputrace.c

@@ -80,6 +80,11 @@ static ssize_t sputrace_read(struct file *file, char __user *buf,
 		char tbuf[128];
 		int width;
 
+		/* If we have data ready to return, don't block waiting
+		 * for more */
+		if (cnt > 0 && sputrace_used() == 0)
+			break;
+
 		error = wait_event_interruptible(sputrace_wait,
 						 sputrace_used() > 0);
 		if (error)