1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * SDK7786 FPGA PCIe mux handling
4  *
5  * Copyright (C) 2010  Paul Mundt
6  */
7 #define pr_fmt(fmt) "PCI: " fmt
8 
9 #include <linux/init.h>
10 #include <linux/kernel.h>
11 #include <linux/pci.h>
12 #include <mach/fpga.h>
13 
14 /*
15  * The SDK7786 FPGA supports mangling of most of the slots in some way or
16  * another. Slots 3/4 are special in that only one can be supported at a
17  * time, and both appear on port 3 to the PCI bus scan. Enabling slot 4
18  * (the horizontal edge connector) will disable slot 3 entirely.
19  *
20  * Misconfigurations can be detected through the FPGA via the slot
21  * resistors to determine card presence. Hotplug remains unsupported.
22  */
23 static unsigned int slot4en __initdata;
24 
25 char *__init pcibios_setup(char *str)
26 {
27 	if (strcmp(str, "slot4en") == 0) {
28 		slot4en = 1;
29 		return NULL;
30 	}
31 
32 	return str;
33 }
34 
35 static int __init sdk7786_pci_init(void)
36 {
37 	u16 data = fpga_read_reg(PCIECR);
38 
39 	/*
40 	 * Enable slot #4 if it's been specified on the command line.
41 	 *
42 	 * Optionally reroute if slot #4 has a card present while slot #3
43 	 * does not, regardless of command line value.
44 	 *
45 	 * Card presence is logically inverted.
46 	 */
47 	slot4en ?: (!(data & PCIECR_PRST4) && (data & PCIECR_PRST3));
48 	if (slot4en) {
49 		pr_info("Activating PCIe slot#4 (disabling slot#3)\n");
50 
51 		data &= ~PCIECR_PCIEMUX1;
52 		fpga_write_reg(data, PCIECR);
53 
54 		/* Warn about forced rerouting if slot#3 is occupied */
55 		if ((data & PCIECR_PRST3) == 0) {
56 			pr_warning("Unreachable card detected in slot#3\n");
57 			return -EBUSY;
58 		}
59 	} else
60 		pr_info("PCIe slot#4 disabled\n");
61 
62 	return 0;
63 }
64 postcore_initcall(sdk7786_pci_init);
65