[PATCH v2 1/2] mbuf: fix Tx checksum offload API doc

[Thomas Monjalon <thomas@monjalon.net>]

When introducing rte_eth_tx_prepare(), the constraints on checksum
pre-filling for Tx offloads were relaxed because implemented in
the PMDs with rte_net_intel_cksum_flags_prepare() helper.
As a consequence, these old requirements are removed for:
	- PKT_TX_OUTER_IP_CKSUM
	- PKT_TX_IP_CKSUM
	- PKT_TX_[L4]_CKSUM
	- PKT_TX_TCP_SEG

Not sure SCTP offload is properly implemented though.

A reference to rte_eth_tx_prepare() is added in rte_eth_tx_burst() doc.

Fixes: 609dd68ef14f ("mbuf: enhance the API documentation of offload flags")
Fixes: 4fb7e803eb1a ("ethdev: add Tx preparation")
Cc: stable@dpdk.org

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
---
 lib/librte_ether/rte_ethdev.h |  3 +++
 lib/librte_mbuf/rte_mbuf.h    | 16 +++-------------
 2 files changed, 6 insertions(+), 13 deletions(-)

diff --git a/lib/librte_ether/rte_ethdev.h b/lib/librte_ether/rte_ethdev.h
index 7e4e57b3c..eb090df9a 100644
--- a/lib/librte_ether/rte_ethdev.h
+++ b/lib/librte_ether/rte_ethdev.h
@@ -3911,6 +3911,9 @@ static inline int rte_eth_tx_descriptor_status(uint16_t port_id,
  * invoke this function concurrently on the same tx queue without SW lock.
  * @see rte_eth_dev_info_get, struct rte_eth_txconf::txq_flags
  *
+ * @see rte_eth_tx_prepare to perform some prior checks or adjustments
+ * for offloads.
+ *
  * @param port_id
  *   The port identifier of the Ethernet device.
  * @param queue_id
diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
index 06eceba37..029822226 100644
--- a/lib/librte_mbuf/rte_mbuf.h
+++ b/lib/librte_mbuf/rte_mbuf.h
@@ -226,12 +226,8 @@ extern "C" {
  *  - set the PKT_TX_TCP_SEG flag in mbuf->ol_flags (this flag implies
  *    PKT_TX_TCP_CKSUM)
  *  - set the flag PKT_TX_IPV4 or PKT_TX_IPV6
- *  - if it's IPv4, set the PKT_TX_IP_CKSUM flag and write the IP checksum
- *    to 0 in the packet
+ *  - if it's IPv4, set the PKT_TX_IP_CKSUM flag
  *  - fill the mbuf offload information: l2_len, l3_len, l4_len, tso_segsz
- *  - calculate the pseudo header checksum without taking ip_len in account,
- *    and set it in the TCP header. Refer to rte_ipv4_phdr_cksum() and
- *    rte_ipv6_phdr_cksum() that can be used as helpers.
  */
 #define PKT_TX_TCP_SEG       (1ULL << 50)
 
@@ -244,9 +240,6 @@ extern "C" {
  *  - fill l2_len and l3_len in mbuf
  *  - set the flags PKT_TX_TCP_CKSUM, PKT_TX_SCTP_CKSUM or PKT_TX_UDP_CKSUM
  *  - set the flag PKT_TX_IPV4 or PKT_TX_IPV6
- *  - calculate the pseudo header checksum and set it in the L4 header (only
- *    for TCP or UDP). See rte_ipv4_phdr_cksum() and rte_ipv6_phdr_cksum().
- *    For SCTP, set the crc field to 0.
  */
 #define PKT_TX_L4_NO_CKSUM   (0ULL << 52) /**< Disable L4 cksum of TX pkt. */
 #define PKT_TX_TCP_CKSUM     (1ULL << 52) /**< TCP cksum of TX pkt. computed by NIC. */
@@ -258,7 +251,6 @@ extern "C" {
  * Offload the IP checksum in the hardware. The flag PKT_TX_IPV4 should
  * also be set by the application, although a PMD will only check
  * PKT_TX_IP_CKSUM.
- *  - set the IP checksum field in the packet to 0
  *  - fill the mbuf offload information: l2_len, l3_len
  */
 #define PKT_TX_IP_CKSUM      (1ULL << 54)
@@ -288,10 +280,8 @@ extern "C" {
 
 /**
  * Offload the IP checksum of an external header in the hardware. The
- * flag PKT_TX_OUTER_IPV4 should also be set by the application, alto ugh
- * a PMD will only check PKT_TX_IP_CKSUM.  The IP checksum field in the
- * packet must be set to 0.
- *  - set the outer IP checksum field in the packet to 0
+ * flag PKT_TX_OUTER_IPV4 should also be set by the application, although
+ * a PMD will only check PKT_TX_OUTER_IP_CKSUM.
  *  - fill the mbuf offload information: outer_l2_len, outer_l3_len
  */
 #define PKT_TX_OUTER_IP_CKSUM   (1ULL << 58)
-- 
2.16.2