netdev - RE: [Intel-wired-lan] [PATCH iwl-net v3] i40e: fix Jumbo Frame support after iPXE boot

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Message-ID: <IA1PR11MB62418D6573EBE73C3762C9B18B03A@IA1PR11MB6241.namprd11.prod.outlook.com>
Date: Fri, 5 Sep 2025 11:49:04 +0000
From: "Rinitha, SX" <sx.rinitha@...el.com>
To: "Keller, Jacob E" <jacob.e.keller@...el.com>, Intel Wired LAN
	<intel-wired-lan@...ts.osuosl.org>, "Nguyen, Anthony L"
	<anthony.l.nguyen@...el.com>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>
CC: "Keller, Jacob E" <jacob.e.keller@...el.com>
Subject: RE: [Intel-wired-lan] [PATCH iwl-net v3] i40e: fix Jumbo Frame
 support after iPXE boot

> -----Original Message-----
> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of Jacob Keller
> Sent: 28 August 2025 02:48
> To: Intel Wired LAN <intel-wired-lan@...ts.osuosl.org>; Nguyen, Anthony L <anthony.l.nguyen@...el.com>; netdev@...r.kernel.org
> Cc: Keller, Jacob E <jacob.e.keller@...el.com>
> Subject: [Intel-wired-lan] [PATCH iwl-net v3] i40e: fix Jumbo Frame support after iPXE boot
>
> The i40e hardware has multiple hardware settings which define the Maximum Frame Size (MFS) of the physical port. The firmware has an AdminQ command
(0x0603) to configure the MFS, but the i40e Linux driver never issues this command.
>
> In most cases this is no problem, as the NVM default value has the device configured for its maximum value of 9728. Unfortunately, recent versions of the iPXE intelxl driver now issue the 0x0603 Set Mac Config command, modifying the MFS and reducing it from its default value of 9728.
>
> This occurred as part of iPXE commit 6871a7de705b ("[intelxl] Use admin queue to set port MAC address and maximum frame size"), a prerequisite change for supporting the E800 series hardware in iPXE. Both the E700 and
> E800 firmware support the AdminQ command, and the iPXE code shares much of the logic between the two device drivers.
>
> The ice E800 Linux driver already issues the 0x0603 Set Mac Config command early during probe, and is thus unaffected by the iPXE change.
>
> Since commit 3a2c6ced90e1 ("i40e: Add a check to see if MFS is set"), the i40e driver does check the I40E_PRTGL_SAH register, but it only logs a warning message if its value is below the 9728 default. This register also only covers received packets and not transmitted packets. A warning can inform system administrators, but does not correct the issue. No interactions from userspace cause the driver to write to PRTGL_SAH or issue the 0x0603 AdminQ command. Only a GLOBR reset will restore the value to its default value. There is no obvious method to trigger a GLOBR reset from user space.
>
> To fix this, introduce the i40e_aq_set_mac_config() function, similar to the one from the ice driver. Call this during early probe to ensure that the device configuration matches driver expectation. Unlike E800, the E700 firmware also has a bit to control whether the MAC should append CRC data.
> It is on by default, but setting a 0 to this bit would disable CRC. The i40e implementation must set this bit to ensure CRC will be appended by the MAC.
>
> In addition to the AQ command, instead of just checking the I40E_PRTGL_SAH register, update its value to the 9728 default and write it back. This ensures that the hardware is in the expected state, regardless of whether the iPXE (or any other early boot driver) has modified this state.
>
> This is a better user experience, as we now fix the issues with larger MTU instead of merely warning. It also aligns with the way the ice E800 series driver works.
>
> A final note: The Fixes tag provided here is not strictly accurate. The issue occurs as a result of an external entity (the iPXE intelxl driver), and this is not a regression specifically caused by the mentioned change.
> However, I believe the original change to just warn about PRTGL_SAH being too low was an insufficient fix.
>
> Fixes: 3a2c6ced90e1 ("i40e: Add a check to see if MFS is set")
> Link: https://github.com/ipxe/ipxe/commit/6871a7de705b6f6a4046f0d19da9bcd689c3bc8e
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
> ---
> Changes in v3:
> - Don't disable CRC. Otherwise, Tx traffic will not be accepted
>  appropriately.
> - Link to v2: https://lore.kernel.org/r/20250815-jk-fix-i40e-ice-pxe-9k-mtu-v2-1-ce857cdc6488@intel.com
>
> Changes in v2:
> - Rewrite commit message with feedback from Paul Menzel.
> - Add missing initialization of cmd via libie_aq_raw().
> - Fix the Kdoc comment for i40e_aq_set_mac_config().
> - Move clarification of the Fixes tag to the commit message.
> - Link to v1: https://lore.kernel.org/r/20250814-jk-fix-i40e-ice-pxe-9k-mtu-v1-1-c3926287fb78@intel.com
> ---
> drivers/net/ethernet/intel/i40e/i40e_adminq_cmd.h |  1 +  drivers/net/ethernet/intel/i40e/i40e_prototype.h  |  2 ++
> drivers/net/ethernet/intel/i40e/i40e_common.c     | 34 +++++++++++++++++++++++
> drivers/net/ethernet/intel/i40e/i40e_main.c       | 17 ++++++++----
> 4 files changed, 48 insertions(+), 6 deletions(-)
>

Tested-by: Rinitha S <sx.rinitha@...el.com> (A Contingent worker at Intel)