csky: Add PCI support

Add the pci related code for csky arch to support basic pci virtual
function, such as qemu virt-pci-9pfs.

Signed-off-by: MaJun <majun258@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@linux.alibaba.com>

arch/csky/include/asm/pci.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef __ASM_CSKY_PCI_H
+#define __ASM_CSKY_PCI_H
+
+#include <linux/types.h>
+#include <linux/slab.h>
+#include <linux/dma-mapping.h>
+
+#include <asm/io.h>
+
+#define PCIBIOS_MIN_IO		0
+#define PCIBIOS_MIN_MEM		0
+
+/* C-SKY shim does not initialize PCI bus */
+#define pcibios_assign_all_busses() 1
+
+extern int isa_dma_bridge_buggy;
+
+#ifdef CONFIG_PCI
+static inline int pci_get_legacy_ide_irq(struct pci_dev *dev, int channel)
+{
+	/* no legacy IRQ on csky */
+	return -ENODEV;
+}
+
+static inline int pci_proc_domain(struct pci_bus *bus)
+{
+	/* always show the domain in /proc */
+	return 1;
+}
+#endif  /* CONFIG_PCI */
+
+#endif  /* __ASM_CSKY_PCI_H */