Re: [PATCH v11] PCI: Add device-specific reset for Qualcomm devices

On Fri, Jun 26, 2026 at 07:50:23AM +0200, 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]>

Couple of comments below, including one bug due to my previous suggestion. Once
those are addressed, feel free to add:

Reviewed-by: Manivannan Sadhasivam <[email protected]>

> ---
> v11: Address Manivannan Sadhasivam feedback:
>   - Remove unused QUALCOMM_WIFI_MHISTATUS define
>   - Use PCI_ERROR_RESPONSE instead of 0xffffffff
>   - Sort device IDs in ascending order (0x0308, 0x1103, 0x1107)
> v10: https://lore.kernel.org/all/[email protected]/
> 
>  drivers/pci/quirks.c | 117 +++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 117 insertions(+)
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 431c021d7414..0de606366200 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -4240,6 +4240,120 @@ 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_MHICTRL			0x38
> +#define QUALCOMM_WIFI_MHICTRL_RESET_MASK	0x2

Qcom calls these WiFi devices as WLAN devices. So I'd prefer to use this term
all around even for function names.

> +
> +/*
> + * 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);
> +	val |= QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET_V;
> +	iowrite32(val, bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> +	ioread32(bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> +
> +	msleep(10);
> +
> +	val &= ~QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET_V;
> +	iowrite32(val, bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> +	ioread32(bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> +
> +	msleep(10);
> +
> +	timeout = jiffies + msecs_to_jiffies(5000);
> +	while (time_before(jiffies, timeout)) {
> +		val = ioread32(bar + QUALCOMM_WIFI_PCIE_SOC_GLOBAL_RESET);
> +		if (val != PCI_ERROR_RESPONSE) {

As Sashiko also pointed out, this will always evaluate to true due to
PCI_ERROR_RESPONSE being ~0ULL. Please use:

	if (!PCI_POSSIBLE_ERROR(val))

Sorry for the wrong suggestion earlier.

- Mani

-- 
மணிவண்ணன் சதாசிவம்