ethtool: Note common alternate exit condition for interrupt coalescing
Many implementations ignore the value of max_frames and do not
treat usecs == 0 as special. Document this as deprecated.
Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/ethtool.h b/include/linux/ethtool.h
index 42378b3..3829712 100644
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -173,6 +173,12 @@
* would cause interrupts to never be generated. To disable
* coalescing, set usecs = 0 and max_frames = 1.
*
+ * Some implementations ignore the value of max_frames and use the
+ * condition:
+ * time_since_first_completion >= usecs
+ * This is deprecated. Drivers for hardware that does not support
+ * counting completions should validate that max_frames == !rx_usecs.
+ *
* Adaptive RX/TX coalescing is an algorithm implemented by some
* drivers to improve latency under low packet rates and improve
* throughput under high packet rates. Some drivers only implement