wishbone: add ioremap comment

pcie-wb/pcie_wb.c

@@ -322,6 +322,18 @@ static int setup_bar(struct pci_dev* pdev, struct pcie_wb_resource* res, int bar
 	if (debug)
 		printk(KERN_ALERT PCIE_WB "/BAR%d: ioremap to %lx\n", bar, (unsigned long)res->addr);
 
+	/* we might consider to change the call to ioremap() instead
+	 * since 5.5. 5.5-rc1 ioremap is equal to ioremap_nocache for all architectures
+	 * source : https://lore.kernel.org/linux-mips/20191209194819.GA28157@lst.de/T/
+	 * that means adding a case
+	 *
+	 *	#elif LINUX_VERSION_CODE < KERNEL_VERSION(5,5,0)
+	 *	#warning Using ioremap_cache (instead of ioremap_nocache)
+	 *	res->addr = ioremap_cache(res->start, res->size);
+	 *	#else
+	 *	res->addr = ioremap(res->start, res->size);
+	 */
+
 	return 0;
 }