MIPS: PCI: Support generic drivers

Introduce support for PCI drivers using only functionality provided
generically by the PCI subsystem, by adding the minimum arch-provided
functions required.

The driver this has been developed for & tested with the xilinx-pcie on
a MIPS Boston development board.
Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/14346/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/Kconfig

@@ -2998,6 +2998,7 @@ config PCI_DOMAINS_GENERIC
 	bool
 
 config PCI_DRIVERS_GENERIC
+	select PCI_DOMAINS_GENERIC if PCI_DOMAINS
 	bool
 
 config PCI_DRIVERS_LEGACY

arch/mips/pci/Makefile

@@ -4,6 +4,7 @@
 
 obj-y				+= pci.o
 obj-$(CONFIG_PCI_DRIVERS_LEGACY)+= pci-legacy.o
+obj-$(CONFIG_PCI_DRIVERS_GENERIC)+= pci-generic.o
 
 #
 # PCI bus host bridge specific code

arch/mips/pci/pci-generic.c

+/*
+ * Copyright (C) 2016 Imagination Technologies
+ * Author: Paul Burton <paul.burton@imgtec.com>
+ *
+ * pcibios_align_resource taken from arch/arm/kernel/bios32.c.
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the
+ * Free Software Foundation;  either version 2 of the  License, or (at your
+ * option) any later version.
+ */
+
+#include <linux/pci.h>
+
+/*
+ * We need to avoid collisions with `mirrored' VGA ports
+ * and other strange ISA hardware, so we always want the
+ * addresses to be allocated in the 0x000-0x0ff region
+ * modulo 0x400.
+ *
+ * Why? Because some silly external IO cards only decode
+ * the low 10 bits of the IO address. The 0x00-0xff region
+ * is reserved for motherboard devices that decode all 16
+ * bits, so it's ok to allocate at, say, 0x2800-0x28ff,
+ * but we want to try to avoid allocating at 0x2900-0x2bff
+ * which might have be mirrored at 0x0100-0x03ff..
+ */
+resource_size_t pcibios_align_resource(void *data, const struct resource *res,
+				resource_size_t size, resource_size_t align)
+{
+	struct pci_dev *dev = data;
+	resource_size_t start = res->start;
+	struct pci_host_bridge *host_bridge;
+
+	if (res->flags & IORESOURCE_IO && start & 0x300)
+		start = (start + 0x3ff) & ~0x3ff;
+
+	start = (start + align - 1) & ~(align - 1);
+
+	host_bridge = pci_find_host_bridge(dev->bus);
+
+	if (host_bridge->align_resource)
+		return host_bridge->align_resource(dev, res,
+				start, size, align);
+
+	return start;
+}
+
+void pcibios_fixup_bus(struct pci_bus *bus)
+{
+	pci_read_bridge_bases(bus);
+}