1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * arch/sh/boards/dreamcast/irq.c
4 *
5 * Holly IRQ support for the Sega Dreamcast.
6 *
7 * Copyright (c) 2001, 2002 M. R. Brown <mrbrown@0xd6.org>
8 *
9 * This file is part of the LinuxDC project (www.linuxdc.org)
10 */
11 #include <linux/irq.h>
12 #include <linux/io.h>
13 #include <linux/export.h>
14 #include <linux/err.h>
15 #include <mach/sysasic.h>
16
17 /*
18 * Dreamcast System ASIC Hardware Events -
19 *
20 * The Dreamcast's System ASIC (a.k.a. Holly) is responsible for receiving
21 * hardware events from system peripherals and triggering an SH7750 IRQ.
22 * Hardware events can trigger IRQs 13, 11, or 9 depending on which bits are
23 * set in the Event Mask Registers (EMRs). When a hardware event is
24 * triggered, its corresponding bit in the Event Status Registers (ESRs)
25 * is set, and that bit should be rewritten to the ESR to acknowledge that
26 * event.
27 *
28 * There are three 32-bit ESRs located at 0xa05f6900 - 0xa05f6908. Event
29 * types can be found in arch/sh/include/mach-dreamcast/mach/sysasic.h.
30 * There are three groups of EMRs that parallel the ESRs. Each EMR group
31 * corresponds to an IRQ, so 0xa05f6910 - 0xa05f6918 triggers IRQ 13,
32 * 0xa05f6920 - 0xa05f6928 triggers IRQ 11, and 0xa05f6930 - 0xa05f6938
33 * triggers IRQ 9.
34 *
35 * In the kernel, these events are mapped to virtual IRQs so that drivers can
36 * respond to them as they would a normal interrupt. In order to keep this
37 * mapping simple, the events are mapped as:
38 *
39 * 6900/6910 - Events 0-31, IRQ 13
40 * 6904/6924 - Events 32-63, IRQ 11
41 * 6908/6938 - Events 64-95, IRQ 9
42 *
43 */
44
45 #define ESR_BASE 0x005f6900 /* Base event status register */
46 #define EMR_BASE 0x005f6910 /* Base event mask register */
47
48 /*
49 * Helps us determine the EMR group that this event belongs to: 0 = 0x6910,
50 * 1 = 0x6920, 2 = 0x6930; also determine the event offset.
51 */
52 #define LEVEL(event) (((event) - HW_EVENT_IRQ_BASE) / 32)
53
54 /* Return the hardware event's bit position within the EMR/ESR */
55 #define EVENT_BIT(event) (((event) - HW_EVENT_IRQ_BASE) & 31)
56
57 /*
58 * For each of these *_irq routines, the IRQ passed in is the virtual IRQ
59 * (logically mapped to the corresponding bit for the hardware event).
60 */
61
62 /* Disable the hardware event by masking its bit in its EMR */
63 static inline void disable_systemasic_irq(struct irq_data *data)
64 {
65 unsigned int irq = data->irq;
66 __u32 emr = EMR_BASE + (LEVEL(irq) << 4) + (LEVEL(irq) << 2);
67 __u32 mask;
68
69 mask = inl(emr);
70 mask &= ~(1 << EVENT_BIT(irq));
71 outl(mask, emr);
72 }
73
74 /* Enable the hardware event by setting its bit in its EMR */
75 static inline void enable_systemasic_irq(struct irq_data *data)
76 {
77 unsigned int irq = data->irq;
78 __u32 emr = EMR_BASE + (LEVEL(irq) << 4) + (LEVEL(irq) << 2);
79 __u32 mask;
80
81 mask = inl(emr);
82 mask |= (1 << EVENT_BIT(irq));
83 outl(mask, emr);
84 }
85
86 /* Acknowledge a hardware event by writing its bit back to its ESR */
87 static void mask_ack_systemasic_irq(struct irq_data *data)
88 {
89 unsigned int irq = data->irq;
90 __u32 esr = ESR_BASE + (LEVEL(irq) << 2);
91 disable_systemasic_irq(data);
92 outl((1 << EVENT_BIT(irq)), esr);
93 }
94
95 struct irq_chip systemasic_int = {
96 .name = "System ASIC",
97 .irq_mask = disable_systemasic_irq,
98 .irq_mask_ack = mask_ack_systemasic_irq,
99 .irq_unmask = enable_systemasic_irq,
100 };
101
102 /*
103 * Map the hardware event indicated by the processor IRQ to a virtual IRQ.
104 */
105 int systemasic_irq_demux(int irq)
106 {
107 __u32 emr, esr, status, level;
108 __u32 j, bit;
109
110 switch (irq) {
111 case 13:
112 level = 0;
113 break;
114 case 11:
115 level = 1;
116 break;
117 case 9:
118 level = 2;
119 break;
120 default:
121 return irq;
122 }
123 emr = EMR_BASE + (level << 4) + (level << 2);
124 esr = ESR_BASE + (level << 2);
125
126 /* Mask the ESR to filter any spurious, unwanted interrupts */
127 status = inl(esr);
128 status &= inl(emr);
129
130 /* Now scan and find the first set bit as the event to map */
131 for (bit = 1, j = 0; j < 32; bit <<= 1, j++) {
132 if (status & bit) {
133 irq = HW_EVENT_IRQ_BASE + j + (level << 5);
134 return irq;
135 }
136 }
137
138 /* Not reached */
139 return irq;
140 }
141
142 void systemasic_irq_init(void)
143 {
144 int irq_base, i;
145
146 irq_base = irq_alloc_descs(HW_EVENT_IRQ_BASE, HW_EVENT_IRQ_BASE,
147 HW_EVENT_IRQ_MAX - HW_EVENT_IRQ_BASE, -1);
148 if (IS_ERR_VALUE(irq_base)) {
149 pr_err("%s: failed hooking irqs\n", __func__);
150 return;
151 }
152
153 for (i = HW_EVENT_IRQ_BASE; i < HW_EVENT_IRQ_MAX; i++)
154 irq_set_chip_and_handler(i, &systemasic_int, handle_level_irq);
155 }