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 + 16:
112 		level = 0;
113 		break;
114 	case 11 + 16:
115 		level = 1;
116 		break;
117 	case 9 + 16:
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 }
156