PCI: designware-ep: Configure Resizable BAR cap to advertise the smallest size

Configure the Resizable BAR capability to advertise the smallest size
(1MB) for a couple of reasons:

- Host side resource allocation of BAR fails for larger sizes
- Endpoint function driver does not allocate memory for all supported
  sizes in the Resizable BAR capability.

If and when there is a usecase required to add more flexibility using
the Resizable BAR capability, this can be revisited.
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
[lorenzo.pieralisi@arm.com: updated commit log]
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>

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

@@ -504,10 +504,32 @@ void dw_pcie_ep_exit(struct dw_pcie_ep *ep)
 	pci_epc_mem_exit(epc);
 }
 
+static unsigned int dw_pcie_ep_find_ext_capability(struct dw_pcie *pci, int cap)
+{
+	u32 header;
+	int pos = PCI_CFG_SPACE_SIZE;
+
+	while (pos) {
+		header = dw_pcie_readl_dbi(pci, pos);
+		if (PCI_EXT_CAP_ID(header) == cap)
+			return pos;
+
+		pos = PCI_EXT_CAP_NEXT(header);
+		if (!pos)
+			break;
+	}
+
+	return 0;
+}
+
 int dw_pcie_ep_init(struct dw_pcie_ep *ep)
 {
+	int i;
 	int ret;
+	u32 reg;
 	void *addr;
+	unsigned int nbars;
+	unsigned int offset;
 	struct pci_epc *epc;
 	struct dw_pcie *pci = to_dw_pcie_from_ep(ep);
 	struct device *dev = pci->dev;
@@ -591,6 +613,18 @@ int dw_pcie_ep_init(struct dw_pcie_ep *ep)
 
 	ep->msix_cap = dw_pcie_ep_find_capability(pci, PCI_CAP_ID_MSIX);
 
+	offset = dw_pcie_ep_find_ext_capability(pci, PCI_EXT_CAP_ID_REBAR);
+	if (offset) {
+		reg = dw_pcie_readl_dbi(pci, offset + PCI_REBAR_CTRL);
+		nbars = (reg & PCI_REBAR_CTRL_NBAR_MASK) >>
+			PCI_REBAR_CTRL_NBAR_SHIFT;
+
+		dw_pcie_dbi_ro_wr_en(pci);
+		for (i = 0; i < nbars; i++, offset += PCI_REBAR_CTRL)
+			dw_pcie_writel_dbi(pci, offset + PCI_REBAR_CAP, 0x0);
+		dw_pcie_dbi_ro_wr_dis(pci);
+	}
+
 	dw_pcie_setup(pci);
 
 	return 0;