[PATCH V2 18/20] accel/amdxdna: Link SR-IOV VFs for power management sequencing

[David Zhang <yidong.zhang@amd.com>]

Add PM device links between Physical Function (PF) supplier and Virtual
Function (VF) consumers via device_link_add() upon SR-IOV enablement.
This ensures the PM core enforces the proper power management sequence:
suspending VFs before the PF, and resuming the PF before VFs. If linking
fails, roll back SR-IOV initialization.

Also add a comment clarifying that pci_disable_sriov() removes VF drivers
before firmware VF contexts are destroyed.

The links are created only when SR-IOV is enabled and are removed
when a VF driver unbinds. Rebinding a VF driver alone is not
supported; to rebind, disable and re-enable SR-IOV by writing 0 and
then the number of VFs to sriov_numvfs, which recreates the VFs and
their links.

Signed-off-by: David Zhang <yidong.zhang@amd.com>
---
 drivers/accel/amdxdna/aie4_sriov.c | 73 ++++++++++++++++++++++++++++++
 1 file changed, 73 insertions(+)

diff --git a/drivers/accel/amdxdna/aie4_sriov.c b/drivers/accel/amdxdna/aie4_sriov.c
index 0eea28f62676..3cad0526087d 100644
--- a/drivers/accel/amdxdna/aie4_sriov.c
+++ b/drivers/accel/amdxdna/aie4_sriov.c
@@ -56,9 +56,74 @@ int aie4_sriov_stop(struct amdxdna_dev_hdl *ndev)
 
 	pci_disable_sriov(pdev);
 	ndev->num_vfs = 0;
+
+	/*
+	 * pci_disable_sriov() removes VF drivers first; call destroy_vfs after
+	 * so firmware VF contexts are not cleared before VF drivers finish cleanup.
+	 */
 	return aie4_destroy_vfs(ndev);
 }
 
+static int aie4_for_each_vfs(struct amdxdna_dev *xdna,
+			     int (*cb)(struct amdxdna_dev *, struct pci_dev *))
+{
+	struct pci_dev *pdev_pf = to_pci_dev(xdna->ddev.dev);
+	struct pci_dev *pdev_vf;
+	int pos, ret;
+	u16 vf_did;
+
+	pos = pci_find_ext_capability(pdev_pf, PCI_EXT_CAP_ID_SRIOV);
+	if (!pos)
+		return 0;
+	ret = pci_read_config_word(pdev_pf, pos + PCI_SRIOV_VF_DID, &vf_did);
+	if (ret) {
+		XDNA_ERR(xdna, "read VF Device ID failed %d", ret);
+		return -ENODEV;
+	}
+
+	for (pdev_vf = pci_get_device(pdev_pf->vendor, vf_did, NULL);
+	     pdev_vf;
+	     pdev_vf = pci_get_device(pdev_pf->vendor, vf_did, pdev_vf)) {
+		if (!pdev_vf->is_virtfn || pdev_vf->physfn != pdev_pf)
+			continue;
+
+		ret = cb(xdna, pdev_vf);
+		if (ret) {
+			/* Release reference on early return. */
+			pci_dev_put(pdev_vf);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int aie4_link_vf(struct amdxdna_dev *xdna, struct pci_dev *pdev_vf)
+{
+	struct pci_dev *pdev_pf = to_pci_dev(xdna->ddev.dev);
+	struct device_link *link;
+
+	/*
+	 * The link is removed when the VF driver unbinds. To rebind VF
+	 * drivers, re-enable SR-IOV via sriov_numvfs (0, then N).
+	 */
+	link = device_link_add(&pdev_vf->dev,   /* consumer = VF */
+			       &pdev_pf->dev,   /* supplier = PF */
+			       DL_FLAG_PM_RUNTIME | DL_FLAG_AUTOREMOVE_CONSUMER);
+	if (!link) {
+		XDNA_ERR(xdna, "Failed to link VF %s", pci_name(pdev_vf));
+		return -EINVAL;
+	}
+
+	XDNA_DBG(xdna, "Linked VF %s", pci_name(pdev_vf));
+	return 0;
+}
+
+static int aie4_link_vfs(struct amdxdna_dev *xdna)
+{
+	return aie4_for_each_vfs(xdna, aie4_link_vf);
+}
+
 static int aie4_sriov_start(struct amdxdna_dev_hdl *ndev, int num_vfs)
 {
 	struct amdxdna_dev *xdna = ndev->aie.xdna;
@@ -76,6 +141,14 @@ static int aie4_sriov_start(struct amdxdna_dev_hdl *ndev, int num_vfs)
 		return ret;
 	}
 
+	ret = aie4_link_vfs(xdna);
+	if (ret) {
+		XDNA_ERR(xdna, "link VFs failed, ret: %d", ret);
+		pci_disable_sriov(pdev);
+		aie4_destroy_vfs(ndev);
+		return ret;
+	}
+
 	ndev->num_vfs = num_vfs;
 	return num_vfs;
 }
-- 
2.34.1