nfp: only try to get to PCIe ctrl memory if BARs are wide enough

For accessing PCIe ctrl memory we depend on the BAR aperture being
large enough to reach all registers.  Since the BAR aperture can
be set in the flash make sure the driver won't oops the kernel
when the PCIe configuration is unusual.
Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/netronome/nfp/nfpcore/nfp6000_pcie.c

@@ -119,6 +119,11 @@
 #define NFP_PCIE_EM                                     0x020000
 #define NFP_PCIE_SRAM                                   0x000000
 
+/* Minimal size of the PCIe cfg memory we depend on being mapped,
+ * queue controller and DMA controller don't have to be covered.
+ */
+#define NFP_PCI_MIN_MAP_SIZE				0x080000
+
 #define NFP_PCIE_P2C_FIXED_SIZE(bar)               (1 << (bar)->bitsize)
 #define NFP_PCIE_P2C_BULK_SIZE(bar)                (1 << (bar)->bitsize)
 #define NFP_PCIE_P2C_GENERAL_TARGET_OFFSET(bar, x) ((x) << ((bar)->bitsize - 2))
@@ -628,8 +633,9 @@ static int enable_bars(struct nfp6000_pcie *nfp, u16 interface)
 
 	/* Configure, and lock, BAR0.0 for General Target use (MSI-X SRAM) */
 	bar = &nfp->bar[0];
-	bar->iomem = ioremap_nocache(nfp_bar_resource_start(bar),
-				     nfp_bar_resource_len(bar));
+	if (nfp_bar_resource_len(bar) >= NFP_PCI_MIN_MAP_SIZE)
+		bar->iomem = ioremap_nocache(nfp_bar_resource_start(bar),
+					     nfp_bar_resource_len(bar));
 	if (bar->iomem) {
 		dev_info(nfp->dev,
 			 "BAR0.0 RESERVED: General Mapping/MSI-X SRAM\n");