PCI: dwc: Don't assume the ops in dw_pcie always exist

Some dwc-based device drivers, especially host-only drivers, may work well
with the default read_dbi/write_dbi/link_up implementations in
pcie-designware.c, so remove the assumption that every driver implements
them to simplify those drivers.

Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Jisheng Zhang <[e-mail]>
Signed-off-by: Lorenzo Pieralisi <[e-mail]>
Signed-off-by: Bjorn Helgaas <[e-mail]>

drivers/pci/controller/dwc/pcie-designware-ep.c

···
 	struct dw_pcie_ep *ep = epc_get_drvdata(epc);
 	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
 
-	if (!pci->ops->stop_link)
-		return;
-
-	pci->ops->stop_link(pci);
+	if (pci->ops && pci->ops->stop_link)
+		pci->ops->stop_link(pci);
 }
 
 static int dw_pcie_ep_start(struct pci_epc *epc)
···
 	struct dw_pcie_ep *ep = epc_get_drvdata(epc);
 	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
 
-	if (!pci->ops->start_link)
+	if (!pci->ops || !pci->ops->start_link)
 		return -EINVAL;
 
 	return pci->ops->start_link(pci);

drivers/pci/controller/dwc/pcie-designware-host.c

···
 	dw_pcie_setup_rc(pp);
 	dw_pcie_msi_init(pp);
 
-	if (!dw_pcie_link_up(pci) && pci->ops->start_link) {
+	if (!dw_pcie_link_up(pci) && pci->ops && pci->ops->start_link) {
 		ret = pci->ops->start_link(pci);
 		if (ret)
 			goto err_free_msi;

drivers/pci/controller/dwc/pcie-designware.c

···
 	int ret;
 	u32 val;
 
-	if (pci->ops->read_dbi)
+	if (pci->ops && pci->ops->read_dbi)
 		return pci->ops->read_dbi(pci, pci->dbi_base, reg, size);
 
 	ret = dw_pcie_read(pci->dbi_base + reg, size, &val);
···
 {
 	int ret;
 
-	if (pci->ops->write_dbi) {
+	if (pci->ops && pci->ops->write_dbi) {
 		pci->ops->write_dbi(pci, pci->dbi_base, reg, size, val);
 		return;
 	}
···
 {
 	int ret;
 
-	if (pci->ops->write_dbi2) {
+	if (pci->ops && pci->ops->write_dbi2) {
 		pci->ops->write_dbi2(pci, pci->dbi_base2, reg, size, val);
 		return;
 	}
···
 	int ret;
 	u32 val;
 
-	if (pci->ops->read_dbi)
+	if (pci->ops && pci->ops->read_dbi)
 		return pci->ops->read_dbi(pci, pci->atu_base, reg, 4);
 
 	ret = dw_pcie_read(pci->atu_base + reg, 4, &val);
···
 {
 	int ret;
 
-	if (pci->ops->write_dbi) {
+	if (pci->ops && pci->ops->write_dbi) {
 		pci->ops->write_dbi(pci, pci->atu_base, reg, 4, val);
 		return;
 	}
···
 {
 	u32 retries, val;
 
-	if (pci->ops->cpu_addr_fixup)
+	if (pci->ops && pci->ops->cpu_addr_fixup)
 		cpu_addr = pci->ops->cpu_addr_fixup(pci, cpu_addr);
 
 	if (pci->iatu_unroll_enabled) {
···
 {
 	u32 val;
 
-	if (pci->ops->link_up)
+	if (pci->ops && pci->ops->link_up)
 		return pci->ops->link_up(pci);
 
 	val = readl(pci->dbi_base + PCIE_PORT_DEBUG1);