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 + bv->bv_offset);
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 blk_qc_t n64cart_submit_bio(struct bio *bio)
88 {
89 struct bio_vec bvec;
90 struct bvec_iter iter;
91 struct device *dev = bio->bi_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 goto io_error;
97 pos += bvec.bv_len;
98 }
99
100 bio_endio(bio);
101 return BLK_QC_T_NONE;
102 io_error:
103 bio_io_error(bio);
104 return BLK_QC_T_NONE;
105 }
106
107 static const struct block_device_operations n64cart_fops = {
108 .owner = THIS_MODULE,
109 .submit_bio = n64cart_submit_bio,
110 };
111
112 /*
113 * The target device is embedded and RAM-constrained. We save RAM
114 * by initializing in __init code that gets dropped late in boot.
115 * For the same reason there is no module or unloading support.
116 */
n64cart_probe(struct platform_device * pdev)117 static int __init n64cart_probe(struct platform_device *pdev)
118 {
119 struct gendisk *disk;
120
121 if (!start || !size) {
122 pr_err("start or size not specified\n");
123 return -ENODEV;
124 }
125
126 if (size & 4095) {
127 pr_err("size must be a multiple of 4K\n");
128 return -ENODEV;
129 }
130
131 reg_base = devm_platform_ioremap_resource(pdev, 0);
132 if (!reg_base)
133 return -EINVAL;
134
135 disk = alloc_disk(0);
136 if (!disk)
137 return -ENOMEM;
138
139 disk->queue = blk_alloc_queue(NUMA_NO_NODE);
140 if (!disk->queue)
141 return -ENOMEM;
142
143 disk->first_minor = 0;
144 disk->flags = GENHD_FL_NO_PART_SCAN | GENHD_FL_EXT_DEVT;
145 disk->fops = &n64cart_fops;
146 disk->private_data = &pdev->dev;
147 strcpy(disk->disk_name, "n64cart");
148
149 set_capacity(disk, size >> SECTOR_SHIFT);
150 set_disk_ro(disk, 1);
151
152 blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
153 blk_queue_physical_block_size(disk->queue, 4096);
154 blk_queue_logical_block_size(disk->queue, 4096);
155
156 add_disk(disk);
157
158 pr_info("n64cart: %u kb disk\n", size / 1024);
159
160 return 0;
161 }
162
163 static struct platform_driver n64cart_driver = {
164 .driver = {
165 .name = "n64cart",
166 },
167 };
168
n64cart_init(void)169 static int __init n64cart_init(void)
170 {
171 return platform_driver_probe(&n64cart_driver, n64cart_probe);
172 }
173
174 module_init(n64cart_init);
175
176 MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
177 MODULE_DESCRIPTION("Driver for the N64 cart");
178 MODULE_LICENSE("GPL");
179