net: ipa: minor update to handling of packet with status

Rearrange some comments and assignments made when handling a packet
that is received with status, aiming to improve understandability.

Use DIV_ROUND_CLOSEST() to get a better per-packet true size estimate.

Signed-off-by: Alex Elder <elder@linaro.org>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ipa/ipa_endpoint.c

@@ -1213,12 +1213,11 @@ static void ipa_endpoint_status_parse(struct ipa_endpoint *endpoint,
 			continue;
 		}
 
-		/* Compute the amount of buffer space consumed by the
-		 * packet, including the status element.  If the hardware
-		 * is configured to pad packet data to an aligned boundary,
-		 * account for that.  And if checksum offload is is enabled
-		 * a trailer containing computed checksum information will
-		 * be appended.
+		/* Compute the amount of buffer space consumed by the packet,
+		 * including the status element.  If the hardware is configured
+		 * to pad packet data to an aligned boundary, account for that.
+		 * And if checksum offload is enabled a trailer containing
+		 * computed checksum information will be appended.
 		 */
 		align = endpoint->data->rx.pad_align ? : 1;
 		len = le16_to_cpu(status->pkt_len);
@@ -1226,16 +1225,21 @@ static void ipa_endpoint_status_parse(struct ipa_endpoint *endpoint,
 		if (endpoint->data->checksum)
 			len += sizeof(struct rmnet_map_dl_csum_trailer);
 
-		/* Charge the new packet with a proportional fraction of
-		 * the unused space in the original receive buffer.
-		 * XXX Charge a proportion of the *whole* receive buffer?
-		 */
 		if (!ipa_status_drop_packet(status)) {
-			u32 extra = unused * len / total_len;
-			void *data2 = data + sizeof(*status);
-			u32 len2 = le16_to_cpu(status->pkt_len);
+			void *data2;
+			u32 extra;
+			u32 len2;
 
 			/* Client receives only packet data (no status) */
+			data2 = data + sizeof(*status);
+			len2 = le16_to_cpu(status->pkt_len);
+
+			/* Have the true size reflect the extra unused space in
+			 * the original receive buffer.  Distribute the "cost"
+			 * proportionately across all aggregated packets in the
+			 * buffer.
+			 */
+			extra = DIV_ROUND_CLOSEST(unused * len, total_len);
 			ipa_endpoint_skb_copy(endpoint, data2, len2, extra);
 		}