PCI: dwc: ep: Enforce DWC specific 64-bit BAR limitation

From the DWC EP databook 5.96a, section "3.5.7.1.4 General Rules for BAR
Setup (Fixed Mask or Programmable Mask Schemes Only)":

"Any pair (for example BARs 0 and 1) can be configured as one 64-bit BAR,
two 32-bit BARs, or one 32-bit BAR."

"BAR pairs cannot overlap to form a 64-bit BAR. For example, you cannot
combine BARs 1 and 2 to form a 64-bit BAR."

While this limitation does exist in some other PCI endpoint controllers,
e.g. cdns_pcie_ep_set_bar(), the limitation does not appear to be defined
in the PCIe specification itself, thus add an explicit check for this in
dw_pcie_ep_set_bar() (rather than pci_epc_set_bar()).

Link: https://lore.kernel.org/linux-pci/20240528134839.8817-2-cassel@kernel.org
Signed-off-by: Niklas Cassel <cassel@kernel.org>
Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>

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

@@ -215,6 +215,13 @@ static int dw_pcie_ep_set_bar(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
 	int ret, type;
 	u32 reg;
 
+	/*
+	 * DWC does not allow BAR pairs to overlap, e.g. you cannot combine BARs
+	 * 1 and 2 to form a 64-bit BAR.
+	 */
+	if ((flags & PCI_BASE_ADDRESS_MEM_TYPE_64) && (bar & 1))
+		return -EINVAL;
+
 	reg = PCI_BASE_ADDRESS_0 + (4 * bar);
 
 	if (!(flags & PCI_BASE_ADDRESS_SPACE))