linux/drivers/block/n64cart.c
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   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 + 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
  87static 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;
 102io_error:
 103        bio_io_error(bio);
 104        return BLK_QC_T_NONE;
 105}
 106
 107static 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 */
 117static 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
 163static struct platform_driver n64cart_driver = {
 164        .driver = {
 165                .name = "n64cart",
 166        },
 167};
 168
 169static int __init n64cart_init(void)
 170{
 171        return platform_driver_probe(&n64cart_driver, n64cart_probe);
 172}
 173
 174module_init(n64cart_init);
 175
 176MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
 177MODULE_DESCRIPTION("Driver for the N64 cart");
 178MODULE_LICENSE("GPL");
 179