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
 16enum {
 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
 32static u32 __iomem *reg_base;
 33
 34static unsigned int start;
 35module_param(start, uint, 0);
 36MODULE_PARM_DESC(start, "Start address of the cart block data");
 37
 38static unsigned int size;
 39module_param(size, uint, 0);
 40MODULE_PARM_DESC(size, "Size of the cart block data, in bytes");
 41
 42static void n64cart_write_reg(const u8 reg, const u32 value)
 43{
 44	writel(value, reg_base + reg);
 45}
 46
 47static u32 n64cart_read_reg(const u8 reg)
 48{
 49	return readl(reg_base + reg);
 50}
 51
 52static 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 */
 62static 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
 87static 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
105static 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 */
115static 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
161out_cleanup_disk:
162	put_disk(disk);
163out:
164	return err;
165}
166
167static struct platform_driver n64cart_driver = {
168	.driver = {
169		.name = "n64cart",
170	},
171};
172
173static int __init n64cart_init(void)
174{
175	return platform_driver_probe(&n64cart_driver, n64cart_probe);
176}
177
178module_init(n64cart_init);
179
180MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
181MODULE_DESCRIPTION("Driver for the N64 cart");
182MODULE_LICENSE("GPL");