drivers/block/n64cart.c

   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
  42 static void n64cart_write_reg(const u8 reg, const u32 value)
  43 {
  44         writel(value, reg_base + reg);
  45 }
  46
  47 static u32 n64cart_read_reg(const u8 reg)
  48 {
  49         return readl(reg_base + reg);
  50 }
  51
  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  */
  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
  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  */
 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
 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");