ethtool: Correct description of 'max_coalesced_frames' fields

The current descriptions state that these fields specify 'How many
packets to delay ... after a packet ...' which implies that the
hardware should wait for (max_coalesced_frames + 1) completions before
generating an interrupt.  It is also stated that setting both this
field and the corresponding 'coalesce_usecs' field to 0 is invalid.
Together, this implies that the hardware must always be configured
to delay a completion IRQ for at least 1 usec or 1 more completion.

I believe that the addition of 1 is not intended, and David Miller
confirms that the original implementation (in tg3) does not do this.
Clarify the descriptions of these fields to avoid this interpretation.

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 71d45a1..18059ca 100644 (file)
--- a/include/linux/ethtool.h
+++ b/include/linux/ethtool.h
@@ -122,8 +122,8 @@ struct ethtool_eeprom {
  * @cmd: ETHTOOL_{G,S}COALESCE
  * @rx_coalesce_usecs: How many usecs to delay an RX interrupt after
  *     a packet arrives.  If 0, only @rx_max_coalesced_frames is used.
- * @rx_max_coalesced_frames: How many packets to delay an RX interrupt
- *     after a packet arrives.  If 0, only @rx_coalesce_usecs is used.
+ * @rx_max_coalesced_frames: Maximum number of packets to receive
+ *     before an RX interrupt.  If 0, only @rx_coalesce_usecs is used.
  * @rx_coalesce_usecs_irq: Same as @rx_coalesce_usecs, except that
  *     this value applies while an IRQ is being serviced by the host.
  * @rx_max_coalesced_frames_irq: Same as @rx_max_coalesced_frames,
@@ -132,9 +132,9 @@ struct ethtool_eeprom {
  * @tx_coalesce_usecs: How many usecs to delay a TX interrupt after
  *     a packet is sent.  If 0, only @tx_max_coalesced_frames
  *     is used.
- * @tx_max_coalesced_frames: How many packets to delay a TX interrupt
- *     after a packet is sent.  If 0, only @tx_coalesce_usecs is
- *     used.
+ * @tx_max_coalesced_frames: Maximum number of packets to be sent
+ *     before a TX interrupt.  If 0, only @tx_coalesce_usecs is
+ *     used.
  * @tx_coalesce_usecs_irq: Same as @tx_coalesce_usecs, except that
  *     this value applies while an IRQ is being serviced by the host.
  * @tx_max_coalesced_frames_irq: Same as @tx_max_coalesced_frames,
@@ -149,21 +149,21 @@ struct ethtool_eeprom {
  * @pkt_rate_low: Threshold for low packet rate (packets per second).
  * @rx_coalesce_usecs_low: How many usecs to delay an RX interrupt after
  *     a packet arrives, when the packet rate is below @pkt_rate_low.
- * @rx_max_coalesced_frames_low: How many packets to delay an RX interrupt
- *     after a packet arrives, when the packet rate is below @pkt_rate_low.
+ * @rx_max_coalesced_frames_low: Maximum number of packets to be received
+ *     before an RX interrupt, when the packet rate is below @pkt_rate_low.
  * @tx_coalesce_usecs_low: How many usecs to delay a TX interrupt after
  *     a packet is sent, when the packet rate is below @pkt_rate_low.
- * @tx_max_coalesced_frames_low: How many packets to delay a TX interrupt
- *     after a packet is sent, when the packet rate is below @pkt_rate_low.
+ * @tx_max_coalesced_frames_low: Maximum nuumber of packets to be sent before
+ *     a TX interrupt, when the packet rate is below @pkt_rate_low.
  * @pkt_rate_high: Threshold for high packet rate (packets per second).
  * @rx_coalesce_usecs_high: How many usecs to delay an RX interrupt after
  *     a packet arrives, when the packet rate is above @pkt_rate_high.
- * @rx_max_coalesced_frames_high: How many packets to delay an RX interrupt
- *     after a packet arrives, when the packet rate is above @pkt_rate_high.
+ * @rx_max_coalesced_frames_high: Maximum number of packets to be received
+ *     before an RX interrupt, when the packet rate is above @pkt_rate_high.
  * @tx_coalesce_usecs_high: How many usecs to delay a TX interrupt after
  *     a packet is sent, when the packet rate is above @pkt_rate_high.
- * @tx_max_coalesced_frames_high: How many packets to delay a TX interrupt
- *     after a packet is sent, when the packet rate is above @pkt_rate_high.
+ * @tx_max_coalesced_frames_high: Maximum number of packets to be sent before
+ *     a TX interrupt, when the packet rate is above @pkt_rate_high.
  * @rate_sample_interval: How often to do adaptive coalescing packet rate
  *     sampling, measured in seconds.  Must not be zero.
  *