Re: [PATCH v9] PCI: Add device-specific reset for Qualcomm devices

On Thu, Jun 18, 2026 at 08:33:08AM +0200, Jose Ignacio Tornos Martinez wrote:
> Hi Mani,
> 
> Let me clarify the exact scenario and where the reset is necessary:
> 
> * For the commented WiFi devices (WCN6855/WCN7850):
> 
> Standard VFIO passthrough flow (this works fine):
>   1. Unbind native driver (ath11k/ath12k/MHI)
>   2. Bind vfio-pci driver
>   3. Assign device to VM
>   4. VM boots, loads its own driver → device works perfectly
>   5. VM shuts down cleanly → device can be reassigned → works fine
> 
> The problem occurs with unclean VM termination:
>   1. VM crashes or is force-terminated
>   2. VFIO tries to reset the device before reassignment
>   3. Without a working PCI reset method, reset fails
>   4. Device stuck in undefined state → cannot be reassigned to another VM
>   
>      Unbinding the driver again doesn't help because the device hardware
>      itself is in a bad state. From hypervisor:
>      $ lspci -vvv -s 0000:03:00.0
>         03:00.0 Network controller: Qualcomm Technologies, Inc (rev ff) (prog-if ff)
>             !!! Unknown header type 7f
>      And a full host power-cycle is necessary to recover.
>      

Can you try the global reset available in the WLAN device BAR space?

WCN6855: https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/tree/drivers/net/wireless/ath/ath11k/pci.c#n193
WCN7850: https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/tree/drivers/net/wireless/ath/ath12k/pci.c#n182

> * For the commented modem devices (SDX62/SDX65): 
> 
> Even worse because it fails during the first VM boot without proper reset
> capability, standard VFIO passthrough flow:
>   1. Unbind native driver (MHI)
>   2. Bind vfio-pci driver
>   3. Assign device to VM
>   4. VM boots, loads its own driver and crashes:
>      [   24.024165] mhi mhi0: Device failed to enter MHI Ready
>      [   24.024168] mhi mhi0: MHI did not enter READY state
>      
>      Unbind/rebind attempts fail:
>      [  352.643601] mhi mhi0: Requested to power ON
>      [  352.643611] mhi mhi0: Power on setup success
>      [  373.442954] mhi mhi0: Device failed to clear MHI Reset
>      [  373.442970] mhi mhi0: MHI did not enter READY state
>      And requires a full host power cycle to recover,
>      even outside of VFIO scenarios.
> 
> * MHI Host driver's remove callback may handle clean software state
> teardown, but it doesn't provide a PCI reset capability that VFIO can
> invoke. VFIO needs a reset method registered in the PCI reset hierarchy
> (device_specific, pm, flr, bus, etc.). VFIO invokes this reset both during
> initial device binding (before the VM starts) and when reassigning the
> device between VMs - without a working reset method, the device cannot
> reach a clean state for initialization.
> 

Likewise, there is a SoC reset available in the modem BAR space. You can try it:
https://git.kernel.org/pub/scm/linux/kernel/git/pci/pci.git/tree/drivers/bus/mhi/host/main.c#n178

If these works, then you can hook these in the device_specific reset callback.

- Mani

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