--- /dev/null
+From 6c3fc0b1c3d073bd6fc3bf43dbd0e64240537464 Mon Sep 17 00:00:00 2001
+From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
+Date: Sun, 7 Jul 2024 08:53:18 -0400
+Subject: igc: Fix qbv tx latency by setting gtxoffset
+
+From: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
+
+commit 6c3fc0b1c3d073bd6fc3bf43dbd0e64240537464 upstream.
+
+A large tx latency issue was discovered during testing when only QBV was
+enabled. The issue occurs because gtxoffset was not set when QBV is
+active, it was only set when launch time is active.
+
+The patch "igc: Correct the launchtime offset" only sets gtxoffset when
+the launchtime_enable field is set by the user. Enabling launchtime_enable
+ultimately sets the register IGC_TXQCTL_QUEUE_MODE_LAUNCHT (referred to as
+LaunchT in the SW user manual).
+
+Section 7.5.2.6 of the IGC i225/6 SW User Manual Rev 1.2.4 states:
+"The latency between transmission scheduling (launch time) and the
+time the packet is transmitted to the network is listed in Table 7-61."
+
+However, the patch misinterprets the phrase "launch time" in that section
+by assuming it specifically refers to the LaunchT register, whereas it
+actually denotes the generic term for when a packet is released from the
+internal buffer to the MAC transmit logic.
+
+This launch time, as per that section, also implicitly refers to the QBV
+gate open time, where a packet waits in the buffer for the QBV gate to
+open. Therefore, latency applies whenever QBV is in use. TSN features such
+as QBU and QAV reuse QBV, making the latency universal to TSN features.
+
+Discussed with i226 HW owner (Shalev, Avi) and we were in agreement that
+the term "launch time" used in Section 7.5.2.6 is not clear and can be
+easily misinterpreted. Avi will update this section to:
+"When TQAVCTRL.TRANSMIT_MODE = TSN, the latency between transmission
+scheduling and the time the packet is transmitted to the network is listed
+in Table 7-61."
+
+Fix this issue by using igc_tsn_is_tx_mode_in_tsn() as a condition to
+write to gtxoffset, aligning with the newly updated SW User Manual.
+
+Tested:
+1. Enrol taprio on talker board
+ base-time 0
+ cycle-time 1000000
+ flags 0x2
+ index 0 cmd S gatemask 0x1 interval1
+ index 0 cmd S gatemask 0x1 interval2
+
+ Note:
+ interval1 = interval for a 64 bytes packet to go through
+ interval2 = cycle-time - interval1
+
+2. Take tcpdump on listener board
+
+3. Use udp tai app on talker to send packets to listener
+
+4. Check the timestamp on listener via wireshark
+
+Test Result:
+100 Mbps: 113 ~193 ns
+1000 Mbps: 52 ~ 84 ns
+2500 Mbps: 95 ~ 223 ns
+
+Note that the test result is similar to the patch "igc: Correct the
+launchtime offset".
+
+Fixes: 790835fcc0cb ("igc: Correct the launchtime offset")
+Signed-off-by: Faizal Rahim <faizal.abdul.rahim@linux.intel.com>
+Reviewed-by: Simon Horman <horms@kernel.org>
+Acked-by: Vinicius Costa Gomes <vinicius.gomes@intel.com>
+Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
+Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
+Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
+---
+ drivers/net/ethernet/intel/igc/igc_tsn.c | 2 +-
+ 1 file changed, 1 insertion(+), 1 deletion(-)
+
+--- a/drivers/net/ethernet/intel/igc/igc_tsn.c
++++ b/drivers/net/ethernet/intel/igc/igc_tsn.c
+@@ -61,7 +61,7 @@ void igc_tsn_adjust_txtime_offset(struct
+ struct igc_hw *hw = &adapter->hw;
+ u16 txoffset;
+
+- if (!is_any_launchtime(adapter))
++ if (!igc_tsn_is_tx_mode_in_tsn(adapter))
+ return;
+
+ switch (adapter->link_speed) {
projects / thirdparty / kernel / stable-queue.git / commitdiff
