drivers/block/n64cart.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 /*
0003  * Support for the N64 cart.
0004  *
0005  * Copyright (c) 2021 Lauri Kasanen
0006  */
0007
0008 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0009 #include <linux/bitops.h>
0010 #include <linux/blkdev.h>
0011 #include <linux/dma-mapping.h>
0012 #include <linux/init.h>
0013 #include <linux/module.h>
0014 #include <linux/platform_device.h>
0015
0016 enum {
0017     PI_DRAM_REG = 0,
0018     PI_CART_REG,
0019     PI_READ_REG,
0020     PI_WRITE_REG,
0021     PI_STATUS_REG,
0022 };
0023
0024 #define PI_STATUS_DMA_BUSY  (1 << 0)
0025 #define PI_STATUS_IO_BUSY   (1 << 1)
0026
0027 #define CART_DOMAIN     0x10000000
0028 #define CART_MAX        0x1FFFFFFF
0029
0030 #define MIN_ALIGNMENT       8
0031
0032 static u32 __iomem *reg_base;
0033
0034 static unsigned int start;
0035 module_param(start, uint, 0);
0036 MODULE_PARM_DESC(start, "Start address of the cart block data");
0037
0038 static unsigned int size;
0039 module_param(size, uint, 0);
0040 MODULE_PARM_DESC(size, "Size of the cart block data, in bytes");
0041
0042 static void n64cart_write_reg(const u8 reg, const u32 value)
0043 {
0044     writel(value, reg_base + reg);
0045 }
0046
0047 static u32 n64cart_read_reg(const u8 reg)
0048 {
0049     return readl(reg_base + reg);
0050 }
0051
0052 static void n64cart_wait_dma(void)
0053 {
0054     while (n64cart_read_reg(PI_STATUS_REG) &
0055         (PI_STATUS_DMA_BUSY | PI_STATUS_IO_BUSY))
0056         cpu_relax();
0057 }
0058
0059 /*
0060  * Process a single bvec of a bio.
0061  */
0062 static bool n64cart_do_bvec(struct device *dev, struct bio_vec *bv, u32 pos)
0063 {
0064     dma_addr_t dma_addr;
0065     const u32 bstart = pos + start;
0066
0067     /* Alignment check */
0068     WARN_ON_ONCE((bv->bv_offset & (MIN_ALIGNMENT - 1)) ||
0069              (bv->bv_len & (MIN_ALIGNMENT - 1)));
0070
0071     dma_addr = dma_map_bvec(dev, bv, DMA_FROM_DEVICE, 0);
0072     if (dma_mapping_error(dev, dma_addr))
0073         return false;
0074
0075     n64cart_wait_dma();
0076
0077     n64cart_write_reg(PI_DRAM_REG, dma_addr);
0078     n64cart_write_reg(PI_CART_REG, (bstart | CART_DOMAIN) & CART_MAX);
0079     n64cart_write_reg(PI_WRITE_REG, bv->bv_len - 1);
0080
0081     n64cart_wait_dma();
0082
0083     dma_unmap_page(dev, dma_addr, bv->bv_len, DMA_FROM_DEVICE);
0084     return true;
0085 }
0086
0087 static void n64cart_submit_bio(struct bio *bio)
0088 {
0089     struct bio_vec bvec;
0090     struct bvec_iter iter;
0091     struct device *dev = bio->bi_bdev->bd_disk->private_data;
0092     u32 pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;
0093
0094     bio_for_each_segment(bvec, bio, iter) {
0095         if (!n64cart_do_bvec(dev, &bvec, pos)) {
0096             bio_io_error(bio);
0097             return;
0098         }
0099         pos += bvec.bv_len;
0100     }
0101
0102     bio_endio(bio);
0103 }
0104
0105 static const struct block_device_operations n64cart_fops = {
0106     .owner      = THIS_MODULE,
0107     .submit_bio = n64cart_submit_bio,
0108 };
0109
0110 /*
0111  * The target device is embedded and RAM-constrained. We save RAM
0112  * by initializing in __init code that gets dropped late in boot.
0113  * For the same reason there is no module or unloading support.
0114  */
0115 static int __init n64cart_probe(struct platform_device *pdev)
0116 {
0117     struct gendisk *disk;
0118     int err = -ENOMEM;
0119
0120     if (!start || !size) {
0121         pr_err("start or size not specified\n");
0122         return -ENODEV;
0123     }
0124
0125     if (size & 4095) {
0126         pr_err("size must be a multiple of 4K\n");
0127         return -ENODEV;
0128     }
0129
0130     reg_base = devm_platform_ioremap_resource(pdev, 0);
0131     if (IS_ERR(reg_base))
0132         return PTR_ERR(reg_base);
0133
0134     disk = blk_alloc_disk(NUMA_NO_NODE);
0135     if (!disk)
0136         goto out;
0137
0138     disk->first_minor = 0;
0139     disk->flags = GENHD_FL_NO_PART;
0140     disk->fops = &n64cart_fops;
0141     disk->private_data = &pdev->dev;
0142     strcpy(disk->disk_name, "n64cart");
0143
0144     set_capacity(disk, size >> SECTOR_SHIFT);
0145     set_disk_ro(disk, 1);
0146
0147     blk_queue_flag_set(QUEUE_FLAG_NONROT, disk->queue);
0148     blk_queue_physical_block_size(disk->queue, 4096);
0149     blk_queue_logical_block_size(disk->queue, 4096);
0150
0151     err = add_disk(disk);
0152     if (err)
0153         goto out_cleanup_disk;
0154
0155     pr_info("n64cart: %u kb disk\n", size / 1024);
0156
0157     return 0;
0158
0159 out_cleanup_disk:
0160     put_disk(disk);
0161 out:
0162     return err;
0163 }
0164
0165 static struct platform_driver n64cart_driver = {
0166     .driver = {
0167         .name = "n64cart",
0168     },
0169 };
0170
0171 static int __init n64cart_init(void)
0172 {
0173     return platform_driver_probe(&n64cart_driver, n64cart_probe);
0174 }
0175
0176 module_init(n64cart_init);
0177
0178 MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
0179 MODULE_DESCRIPTION("Driver for the N64 cart");
0180 MODULE_LICENSE("GPL");