VIRTUAL FUNCTION DRIVER INTERFACE(9)

💖 NAME 💖

okay so bestie, welcome to the Virtual Function Driver Interface — aka VFDI — straight out of the Kernel API Manual. This is the page about the software structures that make a two way communication channel between the VF driver and the PF driver, and that whole situation is literally named Virtual Function Driver Interface (VFDI). 💅✨

🌸 DESCRIPTION 🌸

bestie, this file is packing the software structures used to form that two way communication channel between the VF driver and the PF driver. The name? Virtual Function Driver Interface (VFDI). No cap. 🫶

For VFDI purposes, a page is a memory region with size and alignment of 4K. All addresses are DMA addresses to be used within the domain of the relevant VF. ✨

The only hardware-defined channels for a VF driver to communicate with the PF driver are the event mailboxes (FR_CZ_USR_EV registers). Writing to these registers generates an event with EV_CODE = EV_CODE_USR_EV, USER_QID set to the index of the mailbox, and USER_EV_REG_VALUE set to the value written. The PF driver may direct or disable delivery of these events by setting FR_CZ_USR_EV_CFG. 👑

The PF driver can send arbitrary events to arbitrary event queues. However, for consistency, VFDI events from the PF are defined to follow the same form and be sent to the first event queue assigned to the VF while that queue is enabled by the VF driver. 🦋

The general form of the variable bits of VFDI events is:

0             16                       24   31 | DATA        | TYPE
| SEQ   |

SEQ is a sequence number which should be incremented by 1 (modulo 256) for each event. The sequence numbers used in each direction are independent. 🔥

The VF submits requests of type struct vfdi_req by sending the address of the request (ADDR) in a series of 4 events:

0             16                       24   31 | ADDR[0:15]  |
VFDI_EV_TYPE_REQ_WORD0 | SEQ   | | ADDR[16:31] | VFDI_EV_TYPE_REQ_WORD1
| SEQ+1 | | ADDR[32:47] | VFDI_EV_TYPE_REQ_WORD2 | SEQ+2 | | ADDR[48:63]
| VFDI_EV_TYPE_REQ_WORD3 | SEQ+3 |

The address must be page-aligned. After receiving such a valid series of events, the PF driver will attempt to read the request and write a response to the same address. In case of an invalid sequence of events or a DMA error, there will be no response. 💀

The VF driver may request that the PF driver writes status information into its domain asynchronously. After writing the status, the PF driver will send an event of the form:

0             16                       24   31 | reserved    |
VFDI_EV_TYPE_STATUS    | SEQ   |

In case the VF must be reset for any reason, the PF driver will send an event of the form:

0             16                       24   31 | reserved    |
VFDI_EV_TYPE_RESET     | SEQ   |

It is then the responsibility of the VF driver to request reinitialisation of its queues. 🌀

🎀 SEE ALSO 🎀

Kernel file ./drivers/net/ethernet/sfc/siena/vfdi.h, plus enum vfdi_op(9), struct vfdi_req(9), and struct vfdi_status(9). iykyk, go read the header bestie. 📚💖

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mwah 💋 this page is served from ./drivers/net/ethernet/sfc/siena, dated October 2026, and its footer literally says Virtual Fun...er Interface(9) — iconic truncated name, not me being shady. 🫶✨