PCI: Add device-specific reset for Qualcomm WCN6855/WCN7850 WLAN

Qualcomm WCN6855 (17cb:1103) and WCN7850 (17cb:1107) WLAN devices lack
working reset methods for VFIO passthrough scenarios. These devices have no
FLR capability, advertise NoSoftRst+ (blocking PM reset), and have broken
bus reset.

Standard reset methods were already disabled for these devices by commit
6a4f64c3a3ad ("PCI: Avoid SBR for Qualcomm WCN6855/WCN7850 WiFi,
SDX62/SDX65 modems") because they were not working (quirk_no_bus_reset).

Resets of this device always failed prior to this commit, so VFIO on
the host could not enforce isolation between successive passthrough
users.

If a guest driver deinitialized the device, it may have been functional
if passed through to a subsequent guest, despite the lack of isolation.
Otherwise the device may have been left in an undefined state (e.g., DMA
and interrupts active) and unusable.

Add a device-specific reset method using BAR-space hardware reset
registers that exist in these devices.

WCN6855/WCN7850 WLAN devices use SoC global reset via BAR0 (sequence from
ath11k/ath12k driver: ath11k_pci_soc_global_reset(), ath11k_pci_sw_reset(),
ath11k_mhi_set_mhictrl_reset()):

  - Write/clear reset bit at offset 0x3008
  - Wait for PCIe link recovery (up to 5 seconds)
  - Clear MHI controller SYSERR status at offset 0x38

These are true hardware reset mechanisms (not power management or firmware
error recovery), providing proper device reset for VFIO scenarios.

Testing shows stable operation over 100+ VM crash/reset cycles, compared
to previous approaches that failed after ~30 cycles. Device-specific reset
is position #1 in the reset hierarchy, so these Qualcomm devices will use
hardware reset as their primary reset method.

Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
Acked-by: Alex Williamson <alex@shazbot.org>
Link: https://patch.msgid.link/20261005105436.83962-3-jtornosm@redhat.com

0 files changed, 0 insertions, 0 deletions