Re: [PATCH 0/8] selftests/vfio: igb: 82576 hardware compatibility

[Josh Hilke]

On Fri, May 15, 2026 at 3:04 PM Alex Williamson
<alex.williamson@xxxxxxxxxx> wrote:
>
> This series is based on Josh Hilke's initial igb selftest driver
> posted as:
>
>   https://lore.kernel.org/all/20260511211839.2781731-1-jrhilke@xxxxxxxxxx/
>
> That posting validated the driver against QEMU's emulated igb only; it
> has not been tested on physical 82576 hardware.  Real 82576 silicon
> rejects several of the shortcuts the submitted driver relies on (MAC
> loopback, legacy TX descriptors, read-to-clear EICR, autoneg-based
> link bring-up, and an unbounded fault-recovery story), and adding
> real-hardware coverage is the goal here.
>
> Two of the patches add accommodations specifically for QEMU's emulated
> igb (which does not implement PHY-register-0 bit 14 and does not drive
> STATUS.LU from CTRL.SLU) so that Josh's "run selftests without
> hardware" workflow continues to work.  One of these (RCTL.LBM_MAC)
> deviates from datasheet 8.10.1 guidance; empirically the bit has no
> observable effect on real 82576 because MAC loopback is not
> implemented (3.5.6.2).  See patch 1 for both rationales.

This is great, thanks Alex! I'll integrate your changes and David's
comments on my v1, and mail out our changes as v2.



>
>   1) selftests/vfio: igb: Use PHY internal loopback on 82576
>
>      Replace MAC-loopback-via-RCTL.LBM_MAC and PHY autonegotiation with
>      PHY internal loopback per datasheet 3.5.6.3.1.  Force the MAC link
>      state via CTRL.FRCSPD/FRCDPX/SLU since the descriptor engine
>      otherwise waits for a real negotiated link.  Keep RCTL.LBM_MAC
>      (deviates from 8.10.1 guidance but empirically inert on real
>      hardware per 3.5.6.2) and prefix the loopback setup with a
>      one-shot autoneg-restart PHY write (the next PHY write clears
>      autoneg-enable before autoneg can start, so this is a no-op on
>      real silicon); both are required by QEMU's emulation.  Drop the
>      dead igb_read_phy() and its now-unused macros.
>
>   2) selftests/vfio: igb: Use advanced TX and RX descriptors
>
>      Program SRRCTL.DESCTYPE for advanced one-buffer receive
>      descriptors (datasheet 7.1.5.2, 8.10.2) and build advanced TX data
>      descriptors with DEXT/DTYP/IFCS/EOP/PAYLEN (7.2.2.3) rather than
>      the simplified legacy format the submitted driver used.  Drop the
>      unused legacy TX descriptor macros.
>
>   3) selftests/vfio: igb: Program MSI-X interrupt routing
>
>      Configure GPIE.Multiple_MSIX and GPIE.EIAME (Table 7-47), EIAC
>      and EIAM for vector 0 (8.8.5, 8.8.6), and switch EICR clearing
>      from read-to-clear to write-to-clear (7.3.4.2 / 8.8.5 forbid
>      reading EICR while EIAC is programmed).
>
>   4) selftests/vfio: igb: Extend memcpy completion timeout for line-rate
>      hardware
>
>      The submitted 1 ms cap is well below the 32 ms line-rate floor for
>      a 4 MB transfer at 1 Gb/s.  Bump to ~200 ms (6x margin).
>
>   5) selftests/vfio: igb: Disable PCIe completion timeout retries
>
>      Clear GCR.Completion_Timeout_Resend (datasheet 8.6.1) so the
>      intentional unmapped-IOVA tests do not generate an unbounded
>      stream of retried reads on real hardware.
>
>   6) selftests/vfio: Add vfio_pci_irq_reenable() helper
>
>      New libvfio helper that re-issues VFIO_DEVICE_SET_IRQS against
>      existing eventfds, for drivers that recover from
>      VFIO_DEVICE_RESET without disturbing user-side eventfds (and any
>      fd a test fixture may have cached).
>
>   7) selftests/vfio: igb: Factor hardware programming into igb_hw_init()
>
>      Pure refactor splitting igb_init() into a one-shot outer
>      (region-size check, BAR map, CTRL.RST, IMC, vfio_pci_msix_enable)
>      and a reusable inner that programs the registers CTRL.RST clears.
>
>   8) selftests/vfio: igb: Recover after DMA-read faults
>
>      Add igb_error_reset_and_reinit() and call it from
>      igb_memcpy_wait() on completion timeout.  Datasheet 4.2.1.6.1
>      describes CTRL.RST as the recovery mechanism, but empirically
>      CTRL.RST alone leaves the descriptor engine wedged after a
>      DMA-read fault; the 82576 advertises PCIe FLR (datasheet
>      4.2.1.5.1) and VFIO_DEVICE_RESET drives it.
>
> Testing:
>
>   - Selftest builds clean at every commit (verified bisect-buildable).
>   - QEMU emulated igb via vng on a host kernel built with VFIO and
>     Intel IOMMU enabled: vfio_pci_driver_test 35/35 pass across all
>     four IOMMU mode permutations.
>   - Physical 82576 on Intel Alderlake platform: vfio_pci_driver_test
>     35/35 pass across all four IOMMU mode permutations.
>
> Assisted:
>
>   - Series developed primarily with Claude Opus 4.7 with additional
>     assistance from GPT 5.5.  Spec references spot checked and cross
>     checked against multiple models.
>
> Alex Williamson (8):
>   selftests/vfio: igb: Use PHY internal loopback on 82576
>   selftests/vfio: igb: Use advanced TX and RX descriptors
>   selftests/vfio: igb: Program MSI-X interrupt routing
>   selftests/vfio: igb: Extend memcpy completion timeout for line-rate hardware
>   selftests/vfio: igb: Disable PCIe completion timeout retries
>   selftests/vfio: Add vfio_pci_irq_reenable() helper
>   selftests/vfio: igb: Factor hardware programming into igb_hw_init()
>   selftests/vfio: igb: Recover after DMA-read faults
>
>  .../selftests/vfio/lib/drivers/igb/igb.c      | 318 +++++++++++++-----
>  .../vfio/lib/drivers/igb/registers.h          |  58 +++-
>  .../lib/include/libvfio/vfio_pci_device.h     |   2 +
>  .../selftests/vfio/lib/vfio_pci_device.c      |  22 ++
>  4 files changed, 302 insertions(+), 98 deletions(-)
>
> --
> 2.51.0