Re: [PATCH v10] Add device-specific reset for Qualcomm devices

On Wed, Jun 24, 2026 at 03:47:12PM +0800, Baochen Qiang wrote:
> 
> 
> On 6/24/2026 2:31 AM, Jose Ignacio Tornos Martinez wrote:
> > Some Qualcomm PCIe devices (WCN6855/WCN7850 WiFi cards, 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.
> > 
> > The problem manifests in VFIO passthrough scenarios:
> > 
> > - WCN6855 (17cb:1103) and WCN7850 (17cb:1107) WiFi devices:
> >   Normal VM operation works fine, including clean shutdown/reboot.
> >   However, when the VM terminates uncleanly (crash, force-off), VFIO
> >   attempts to reset the device before it can be assigned to another VM.
> >   Without a working reset method, the device remains in an undefined state,
> >   preventing reuse.
> > 
> > - SDX62/SDX65 (17cb:0308) 5G modems: Never successfully initialize even
> >   on first VM assignment without proper reset capability.
> > 
> > Add device-specific reset methods using BAR-space hardware reset registers
> > that exist in these devices:
> > 
> > - WCN6855/WCN7850 WiFi 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
> > 
> > - SDX62/SDX65 modem devices use MHI SoC reset via BAR0 (sequence from MHI
> >   driver: mhi_soc_reset(), mhi_pci_reset_prepare()):
> >   - Write reset request to offset 0xb0
> >   - Wait 2 seconds for reset completion
> > 
> > These are true hardware reset mechanisms (not power management or firmware
> > error recovery), providing proper device reset for VFIO scenarios.
> > 
> > Testing was performed on desktop platforms with M.2 WiFi and modem cards
> > using M.2-to-PCIe adapters, including extensive force-reset cycling to
> > verify stability.
> > 
> > Signed-off-by: Jose Ignacio Tornos Martinez <[email protected]>
> > ---
> > v10:
> >   - Complete redesign based on maintainer feedback (Manivannan Sadhasivam,
> >     Alex Williamson): use actual hardware reset registers from
> >     device drivers instead of D3hot power cycling
> > v9: https://lore.kernel.org/all/[email protected]/
> > 
> >  drivers/pci/quirks.c | 118 +++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 118 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 431c021d7414..8ad3f214e520 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4240,6 +4240,121 @@ static int reset_hinic_vf_dev(struct pci_dev *pdev, bool probe)
> >  	return 0;
> >  }
> >  
> > +#define QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET	0x3008
> > +#define QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET_V	BIT(0)
> > +#define QUALCOMM_WIFI_MHISTATUS			0x48
> > +#define QUALCOMM_WIFI_MHICTRL			0x38
> > +#define QUALCOMM_WIFI_MHICTRL_RESET_MASK	0x2
> > +
> > +/*
> > + * Qualcomm WiFi device-specific reset using SoC global reset via BAR0
> > + * registers.
> > + */
> > +static int reset_qualcomm_wifi(struct pci_dev *pdev, bool probe)
> > +{
> > +	bool link_recovered = false;
> > +	unsigned long timeout;
> > +	void __iomem *bar;
> > +	u32 val;
> > +	u16 cmd;
> > +
> > +	if (probe)
> > +		return 0;
> > +
> > +	if (pdev->current_state != PCI_D0)
> > +		return -EINVAL;
> > +
> > +	pci_read_config_word(pdev, PCI_COMMAND, &cmd);
> > +	pci_write_config_word(pdev, PCI_COMMAND, cmd | PCI_COMMAND_MEMORY);
> > +
> > +	bar = pci_iomap(pdev, 0, 0);
> > +	if (!bar) {
> > +		pci_write_config_word(pdev, PCI_COMMAND, cmd);
> > +		return -ENODEV;
> > +	}
> > +
> > +	val = ioread32(bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> 
> QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET is beyond the first 4K bar area hence requires MHI
> wakeup before accessing, see [1]. the wakeup callback for WCN6855 is
> ath11k_pci_bus_wake_up() which calls mhi_device_get_sync(). Not sure how this can be done
> here. Maybe Mani can provide some hints?
> 

I don't think the device needs to be waken up before
QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET. ath11k driver wakes up the device for
accessing the MHI interface I believe. Since this callback is not touching MHI,
there is no need to wakeup the device, AFAIK.

- Mani

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