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

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

[Khadem Ullah]

Some BlueField firmware versions (e.g. 24.30.1004) do not support flex item
definitions using FIELD_MODE_FIXED with size set to 0, such as in 'next_header'.
Attempting to use this configuration may result in the following error:

  'unsupported header length field mode (FIXED)'

This is resolved starting from firmware version 24.38.1002.

The patch adds a note to the mlx5 guide explaining the firmware requirement
for such flex item configurations.

Fixes: 16508bfd0816 ('net/mlx5: doc: add flex item specifications in mlx5 guide')
Cc: stable@dpdk.org
Signed-off-by: Khadem Ullah <14pwcse1224@uetpeshawar.edu.pk>
---
 doc/guides/nics/mlx5.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
index c3a350d24e..1b0e3efc41 100644
--- a/doc/guides/nics/mlx5.rst
+++ b/doc/guides/nics/mlx5.rst
@@ -476,6 +476,10 @@ Limitations
   - In flex item configuration, ``next_header.field_base`` value
     must be byte aligned (multiple of 8).
   - Modify field with flex item, the offset must be byte aligned (multiple of 8).
+    .. note::
+     Some firmware versions (e.g. 24.30.1004) do not support
+     ``next_header`` with ``field_mode = FIELD_MODE_FIXED`` and zero size.
+     A newer firmware (e.g. >= 24.38.1002) is required to support this configuration.
 
 - Match on random value:
 
-- 
2.43.0

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

[Dariusz Sosnowski]

+ mlx5 maintainers

On Tue, Jul 08, 2025 at 07:49:21AM -0400, Khadem Ullah wrote:
> Some BlueField firmware versions (e.g. 24.30.1004) do not support flex item
> definitions using FIELD_MODE_FIXED with size set to 0, such as in 'next_header'.
> Attempting to use this configuration may result in the following error:
> 
>   'unsupported header length field mode (FIXED)'
> 
> This is resolved starting from firmware version 24.38.1002.

Could you please share the DPDK version you used and
a code sample with flex item configuration?

I checked internally and I see no change which would trigger
a change in behavior regarding 'unsupported header length field mode (FIXED)' error message.

> 
> The patch adds a note to the mlx5 guide explaining the firmware requirement
> for such flex item configurations.
> 
> Fixes: 16508bfd0816 ('net/mlx5: doc: add flex item specifications in mlx5 guide')
> Cc: stable@dpdk.org
> Signed-off-by: Khadem Ullah <14pwcse1224@uetpeshawar.edu.pk>
> ---
>  doc/guides/nics/mlx5.rst | 4 ++++
>  1 file changed, 4 insertions(+)
> 
> diff --git a/doc/guides/nics/mlx5.rst b/doc/guides/nics/mlx5.rst
> index c3a350d24e..1b0e3efc41 100644
> --- a/doc/guides/nics/mlx5.rst
> +++ b/doc/guides/nics/mlx5.rst
> @@ -476,6 +476,10 @@ Limitations
>    - In flex item configuration, ``next_header.field_base`` value
>      must be byte aligned (multiple of 8).
>    - Modify field with flex item, the offset must be byte aligned (multiple of 8).
> +    .. note::
> +     Some firmware versions (e.g. 24.30.1004) do not support
> +     ``next_header`` with ``field_mode = FIELD_MODE_FIXED`` and zero size.
> +     A newer firmware (e.g. >= 24.38.1002) is required to support this configuration.
>  
>  - Match on random value:
>  
> -- 
> 2.43.0
> 

Best regards,
Dariusz Sosnowski

Re: [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