[PATCH] doc/mlx5: document firmware requirement for flex item

[Khadem Ullah]

Hi Dariusz,

Thanks for the follow-up.

I was using DPDK v23.11 with the following flex item configuration:

{
  "next_header": { "field_mode": "FIELD_MODE_FIXED", "field_size": 0, "field_base": 0 },
  "next_protocol": { "field_mode": "FIELD_MODE_FIXED", "field_size": 8, "field_base": 72 },
  "sample_data": [
    { "field_mode": "FIELD_MODE_FIXED", "field_size": 32, "field_base": 0 },
    { "field_mode": "FIELD_MODE_FIXED", "field_size": 32, "field_base": 32 },
    { "field_mode": "FIELD_MODE_FIXED", "field_size": 32, "field_base": 64 },
    { "field_mode": "FIELD_MODE_FIXED", "field_size": 32, "field_base": 96 }
  ],
  "input_link": [
    { "item": "eth type is 0x08802" }
  ],
  "output_link": [
    { "item": "udp", "next": 17 },
    { "item": "tcp", "next": 6 }
  ]
}

With firmware version 24.30.1004 (MT_0000000704), the following error was produced:

  port-0: flex item #3 creation failed: unsupported header length field mode (FIXED)

After upgrading to firmware version 24.38.1002, the same configuration succeeded.

Example flow after upgrade:

  testpmd> flow flex_item pattern 2 spec 45000000000000000000000001020304 mask FF0000000000000000000000FFFFFFFF
  created pattern #2

  testpmd> flow create 0 ingress pattern eth / ipv4 / udp / flex item is 3 pattern is 2 / end actions mark id 1 / queue index 0 / end
  Flow rule #0 created

It appears this issue was resolved at the firmware level.

Best regards,  
Khadem Ullah