powerpc/powernv/pci: Add helper to check if a PE has a single vendor

Add a helper that determines if all the devices contained in a given PE
are all from the same vendor or not.  This can be useful in determining
if it's okay to make PE-wide changes that may be suitable for some
devices but not for others.

This is used later in the series.

Signed-off-by: Russell Currey <ruscur@russell.cc>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/platforms/powernv/pci-ioda.c

@@ -1718,6 +1718,31 @@ static void pnv_pci_ioda_dma_dev_setup(struct pnv_phb *phb, struct pci_dev *pdev
 	 */
 }
 
+static bool pnv_pci_ioda_pe_single_vendor(struct pnv_ioda_pe *pe)
+{
+	unsigned short vendor = 0;
+	struct pci_dev *pdev;
+
+	if (pe->device_count == 1)
+		return true;
+
+	/* pe->pdev should be set if it's a single device, pe->pbus if not */
+	if (!pe->pbus)
+		return true;
+
+	list_for_each_entry(pdev, &pe->pbus->devices, bus_list) {
+		if (!vendor) {
+			vendor = pdev->vendor;
+			continue;
+		}
+
+		if (pdev->vendor != vendor)
+			return false;
+	}
+
+	return true;
+}
+
 static int pnv_pci_ioda_dma_set_mask(struct pci_dev *pdev, u64 dma_mask)
 {
 	struct pci_controller *hose = pci_bus_to_host(pdev->bus);