i40e: fix Jumbo Frame support after iPXE boot

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@intel.com>
Signed-off-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Michal Schmidt <mschmidt@redhat.com>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>