1 // SPDX-License-Identifier: GPL-2.0
2 /*
3 * Support for the N64 cart.
4 *
5 * Copyright (c) 2021 Lauri Kasanen
6 */
7
8 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
9 #include <linux/bitops.h>
10 #include <linux/blkdev.h>
11 #include <linux/dma-mapping.h>
12 #include <linux/init.h>
13 #include <linux/module.h>
14 #include <linux/platform_device.h>
15
16 enum {
17 PI_DRAM_REG = 0,
18 PI_CART_REG,
19 PI_READ_REG,
20 PI_WRITE_REG,
21 PI_STATUS_REG,
22 };
23
24 #define PI_STATUS_DMA_BUSY (1 << 0)
25 #define PI_STATUS_IO_BUSY (1 << 1)
26
27 #define CART_DOMAIN 0x10000000
28 #define CART_MAX 0x1FFFFFFF
29
30 #define MIN_ALIGNMENT 8
31
32 static u32 __iomem *reg_base;
33
34 static unsigned int start;
35 module_param(start, uint, 0);
36 MODULE_PARM_DESC(start, "Start address of the cart block data");
37
38 static unsigned int size;
39 module_param(size, uint, 0);
40 MODULE_PARM_DESC(size, "Size of the cart block data, in bytes");
41
n64cart_write_reg(const u8 reg,const u32 value)42 static void n64cart_write_reg(const u8 reg, const u32 value)
43 {
44 writel(value, reg_base + reg);
45 }
46
n64cart_read_reg(const u8 reg)47 static u32 n64cart_read_reg(const u8 reg)
48 {
49 return readl(reg_base + reg);
50 }
51
n64cart_wait_dma(void)52 static void n64cart_wait_dma(void)
53 {
54 while (n64cart_read_reg(PI_STATUS_REG) &
55 (PI_STATUS_DMA_BUSY | PI_STATUS_IO_BUSY))
56 cpu_relax();
57 }
58
59 /*
60 * Process a single bvec of a bio.
61 */
n64cart_do_bvec(struct device * dev,struct bio_vec * bv,u32 pos)62 static bool n64cart_do_bvec(struct device *dev, struct bio_vec *bv, u32 pos)
63 {
64 dma_addr_t dma_addr;
65 const u32 bstart = pos + start;
66
67 /* Alignment check */
68 WARN_ON_ONCE((bv->bv_offset & (MIN_ALIGNMENT - 1)) ||
69 (bv->bv_len & (MIN_ALIGNMENT - 1)));
70
71 dma_addr = dma_map_bvec(dev, bv, DMA_FROM_DEVICE, 0);
72 if (dma_mapping_error(dev, dma_addr))
73 return false;
74
75 n64cart_wait_dma();
76
77 n64cart_write_reg(PI_DRAM_REG, dma_addr);
78 n64cart_write_reg(PI_CART_REG, (bstart | CART_DOMAIN) & CART_MAX);
79 n64cart_write_reg(PI_WRITE_REG, bv->bv_len - 1);
80
81 n64cart_wait_dma();
82
83 dma_unmap_page(dev, dma_addr, bv->bv_len, DMA_FROM_DEVICE);
84 return true;
85 }
86
n64cart_submit_bio(struct bio * bio)87 static void n64cart_submit_bio(struct bio *bio)
88 {
89 struct bio_vec bvec;
90 struct bvec_iter iter;
91 struct device *dev = bio->bi_bdev->bd_disk->private_data;
92 u32 pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;
93
94 bio_for_each_segment(bvec, bio, iter) {
95 if (!n64cart_do_bvec(dev, &bvec, pos)) {
96 bio_io_error(bio);
97 return;
98 }
99 pos += bvec.bv_len;
100 }
101
102 bio_endio(bio);
103 }
104
105 static const struct block_device_operations n64cart_fops = {
106 .owner = THIS_MODULE,
107 .submit_bio = n64cart_submit_bio,
108 };
109
110 /*
111 * The target device is embedded and RAM-constrained. We save RAM
112 * by initializing in __init code that gets dropped late in boot.
113 * For the same reason there is no module or unloading support.
114 */
n64cart_probe(struct platform_device * pdev)115 static int __init n64cart_probe(struct platform_device *pdev)
116 {
117 struct queue_limits lim = {
118 .physical_block_size = 4096,
119 .logical_block_size = 4096,
120 };
121 struct gendisk *disk;
122 int err = -ENOMEM;
123
124 if (!start || !size) {
125 pr_err("start or size not specified\n");
126 return -ENODEV;
127 }
128
129 if (size & 4095) {
130 pr_err("size must be a multiple of 4K\n");
131 return -ENODEV;
132 }
133
134 reg_base = devm_platform_ioremap_resource(pdev, 0);
135 if (IS_ERR(reg_base))
136 return PTR_ERR(reg_base);
137
138 disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
139 if (IS_ERR(disk)) {
140 err = PTR_ERR(disk);
141 goto out;
142 }
143
144 disk->first_minor = 0;
145 disk->flags = GENHD_FL_NO_PART;
146 disk->fops = &n64cart_fops;
147 disk->private_data = &pdev->dev;
148 strcpy(disk->disk_name, "n64cart");
149
150 set_capacity(disk, size >> SECTOR_SHIFT);
151 set_disk_ro(disk, 1);
152
153 err = add_disk(disk);
154 if (err)
155 goto out_cleanup_disk;
156
157 pr_info("n64cart: %u kb disk\n", size / 1024);
158
159 return 0;
160
161 out_cleanup_disk:
162 put_disk(disk);
163 out:
164 return err;
165 }
166
167 static struct platform_driver n64cart_driver = {
168 .driver = {
169 .name = "n64cart",
170 },
171 };
172
n64cart_init(void)173 static int __init n64cart_init(void)
174 {
175 return platform_driver_probe(&n64cart_driver, n64cart_probe);
176 }
177
178 module_init(n64cart_init);
179
180 MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
181 MODULE_DESCRIPTION("Driver for the N64 cart");
182 MODULE_LICENSE("GPL");
183