Re: [PATCH v15 0/2] PCI: Add device-specific reset for Qualcomm devices

[Bjorn Helgaas]

On Mon, Oct 05, 2026 at 12:54:34PM +0200, Jose Ignacio Tornos Martinez wrote:
> Some Qualcomm PCIe devices (WCN6855, WCN7850 WLAN; SDX62/SDX65 modems)
> 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).
> 
> VFIO attempts to reset devices on every reassignment:
> - For the listed modems, without a proper reset capability, these devices
> never successfully initialize even on first VM assignment.
> - For the listed WLAN devices, without a working reset method, the attempt
> fails. On clean VM shutdown, the guest driver properly deinitializes the
> device via .shutdown/.remove callbacks, leaving it in a usable state despite
> the failed reset. However, on unclean VM termination (crash, force-off), the
> guest driver callbacks are not triggered, the device remains in an undefined
> state (DMA active, interrupts enabled, etc.), and without a working reset it
> cannot be reused.
> 
> Add device-specific reset methods using BAR-space hardware reset registers
> that exist in these devices:
> 
>   Patch 1: SDX62/SDX65 modem reset via MHI SoC reset
>   Patch 2: WCN6855/WCN7850 WLAN reset via SoC global reset
> 
> These are true hardware reset mechanisms (not power management or firmware
> error recovery), providing proper device reset for VFIO scenarios, allowing
> to enforce isolation between successive passthrough users.
> 
> Testing shows stable operation over 100+ VM crash/reset cycles. Device-
> specific reset is position #1 in the reset hierarchy, so these devices
> will use hardware reset as their primary reset method.
> 
> Jose Ignacio Tornos Martinez (2):
>   PCI: Add device-specific reset for Qualcomm SDX62/SDX65 modems
>   PCI: Add device-specific reset for Qualcomm WCN6855/WCN7850 WLAN
> 
>  drivers/pci/quirks.c | 116 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 116 insertions(+)

Applied to pci/reset for v7.4, thanks!

> ---
> v15: Address Bjorn Helgaas feedback:
>   - Explain the relationship with 6a4f64c3a3ad ("PCI: Avoid SBR for Qualcomm
>     WCN6855/WCN7850 WiFi, SDX62/SDX65 modems") and previous status.
>   - No code changes from v14, only commit message clarifications (Mani's
>     Reviewed-by and Alex's Acked-by retained)
> v14: https://lore.kernel.org/all/20260917071651.14174-1-jtornosm@xxxxxxxxxx/
> 
> --
> 2.54.0
>