cxl: abort cxl_pci_enable_device_hook() if PCI channel is offline

cxl_pci_enable_device_hook() is called when attempting to enable an AFU
sitting on a vPHB. At present, the state of the underlying CXL card's PCI
channel is only checked when it calls cxl_afu_check_and_enable() at the
very end, after it has already set DMA options and initialised a default
context.

Check the CXL card's link status before setting DMA options or initialising
a default context. If the link is down, print a warning and return
immediately.
Signed-off-by: Andrew Donnellan <andrew.donnellan@au1.ibm.com>
Acked-by: Ian Munsie <imunsie@au1.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

drivers/misc/cxl/vphb.c

@@ -48,6 +48,12 @@ static bool cxl_pci_enable_device_hook(struct pci_dev *dev)
 
 	phb = pci_bus_to_host(dev->bus);
 	afu = (struct cxl_afu *)phb->private_data;
+
+	if (!cxl_adapter_link_ok(afu->adapter)) {
+		dev_warn(&dev->dev, "%s: Device link is down, refusing to enable AFU\n", __func__);
+		return false;
+	}
+
 	set_dma_ops(&dev->dev, &dma_direct_ops);
 	set_dma_offset(&dev->dev, PAGE_OFFSET);