[PATCH v14 1/2] PCI: Add device-specific reset for Qualcomm SDX62/SDX65 modems

[Jose Ignacio Tornos Martinez <jtornosm@redhat.com>]

Qualcomm SDX62/SDX65 5G modems (17cb:0308) lack working reset methods for
VFIO passthrough scenarios. These devices have no FLR capability, advertise
NoSoftRst+ (blocking PM reset), and have broken bus reset (addressed by
quirk_no_bus_reset, merged for v7.2).

VFIO attempts to reset devices on every reassignment. Without a proper
reset capability, these devices never successfully initialize even on first
VM assignment.

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

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

This is a true hardware reset mechanism (not power management or firmware
error recovery), providing proper device reset for VFIO scenarios.

Testing shows stable operation over 109 VM crash/reset 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>
Reviewed-by: Manivannan Sadhasivam <mani@kernel.org>
---
v14: Address Bjorn Helgaas feedback:
  - Split WLAN and modem resets into two separate patches
  - No code changes from v13, only patch split and commit message
    clarification (Mani's Reviewed-by retained)
v13: https://lore.kernel.org/all/20260915223634.GA878346@bhelgaas/

 drivers/pci/quirks.c | 40 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 40 insertions(+)

diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index de9bbccda21f..e72af7d2c775 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -4230,6 +4230,45 @@ static int reset_hinic_vf_dev(struct pci_dev *pdev, bool probe)
 	return 0;
 }
 
+#define MHI_SOC_RESET_REQ_OFFSET		0xb0
+#define MHI_SOC_RESET_REQ			BIT(0)
+
+/*
+ * Qualcomm modem device-specific reset using MHI SoC reset via BAR0
+ * register.
+ */
+static int reset_qualcomm_modem(struct pci_dev *pdev, bool probe)
+{
+	void __iomem *bar;
+	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;
+	}
+
+	iowrite32(MHI_SOC_RESET_REQ, bar + MHI_SOC_RESET_REQ_OFFSET);
+	ioread32(bar + MHI_SOC_RESET_REQ_OFFSET);
+
+	/* Be sure device reset has been executed */
+	msleep(2000);
+
+	pci_iounmap(pdev, bar);
+	pci_write_config_word(pdev, PCI_COMMAND, cmd);
+
+	return 0;
+}
+
 static const struct pci_dev_reset_methods pci_dev_reset_methods[] = {
 	{ PCI_VENDOR_ID_INTEL, PCI_DEVICE_ID_INTEL_82599_SFP_VF,
 		 reset_intel_82599_sfp_virtfn },
@@ -4245,6 +4284,7 @@ static const struct pci_dev_reset_methods pci_dev_reset_methods[] = {
 		reset_chelsio_generic_dev },
 	{ PCI_VENDOR_ID_HUAWEI, PCI_DEVICE_ID_HINIC_VF,
 		reset_hinic_vf_dev },
+	{ PCI_VENDOR_ID_QCOM, 0x0308, reset_qualcomm_modem }, /* SDX62/SDX65 modems */
 	{ 0 }
 };
 
-- 
2.54.0