// SPDX-License-Identifier: GPL-2.0
/*
 * Support for the N64 cart.
 *
 * Copyright (c) 2021 Lauri Kasanen
 */

#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
#include <linux/bitops.h>
#include <linux/blkdev.h>
#include <linux/dma-mapping.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/platform_device.h>

enum {
        PI_DRAM_REG = 0,
        PI_CART_REG,
        PI_READ_REG,
        PI_WRITE_REG,
        PI_STATUS_REG,
};

#define PI_STATUS_DMA_BUSY      (1 << 0)
#define PI_STATUS_IO_BUSY       (1 << 1)

#define CART_DOMAIN             0x10000000
#define CART_MAX                0x1FFFFFFF

#define MIN_ALIGNMENT           8

static u32 __iomem *reg_base;

static unsigned int start;
module_param(start, uint, 0);
MODULE_PARM_DESC(start, "Start address of the cart block data");

static unsigned int size;
module_param(size, uint, 0);
MODULE_PARM_DESC(size, "Size of the cart block data, in bytes");

static void n64cart_write_reg(const u8 reg, const u32 value)
{
        writel(value, reg_base + reg);
}

static u32 n64cart_read_reg(const u8 reg)
{
        return readl(reg_base + reg);
}

static void n64cart_wait_dma(void)
{
        while (n64cart_read_reg(PI_STATUS_REG) &
                (PI_STATUS_DMA_BUSY | PI_STATUS_IO_BUSY))
                cpu_relax();
}

/*
 * Process a single bvec of a bio.
 */
static bool n64cart_do_bvec(struct device *dev, struct bio_vec *bv, u32 pos)
{
        dma_addr_t dma_addr;
        const u32 bstart = pos + start;

        /* Alignment check */
        WARN_ON_ONCE((bv->bv_offset & (MIN_ALIGNMENT - 1)) ||
                     (bv->bv_len & (MIN_ALIGNMENT - 1)));

        dma_addr = dma_map_bvec(dev, bv, DMA_FROM_DEVICE, 0);
        if (dma_mapping_error(dev, dma_addr))
                return false;

        n64cart_wait_dma();

        n64cart_write_reg(PI_DRAM_REG, dma_addr);
        n64cart_write_reg(PI_CART_REG, (bstart | CART_DOMAIN) & CART_MAX);
        n64cart_write_reg(PI_WRITE_REG, bv->bv_len - 1);

        n64cart_wait_dma();

        dma_unmap_page(dev, dma_addr, bv->bv_len, DMA_FROM_DEVICE);
        return true;
}

static void n64cart_submit_bio(struct bio *bio)
{
        struct bio_vec bvec;
        struct bvec_iter iter;
        struct device *dev = bio->bi_bdev->bd_disk->private_data;
        u32 pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;

        bio_for_each_segment(bvec, bio, iter) {
                if (!n64cart_do_bvec(dev, &bvec, pos)) {
                        bio_io_error(bio);
                        return;
                }
                pos += bvec.bv_len;
        }

        bio_endio(bio);
}

static const struct block_device_operations n64cart_fops = {
        .owner          = THIS_MODULE,
        .submit_bio     = n64cart_submit_bio,
};

/*
 * The target device is embedded and RAM-constrained. We save RAM
 * by initializing in __init code that gets dropped late in boot.
 * For the same reason there is no module or unloading support.
 */
static int __init n64cart_probe(struct platform_device *pdev)
{
        struct queue_limits lim = {
                .physical_block_size    = 4096,
                .logical_block_size     = 4096,
        };
        struct gendisk *disk;
        int err = -ENOMEM;

        if (!start || !size) {
                pr_err("start or size not specified\n");
                return -ENODEV;
        }

        if (size & 4095) {
                pr_err("size must be a multiple of 4K\n");
                return -ENODEV;
        }

        reg_base = devm_platform_ioremap_resource(pdev, 0);
        if (IS_ERR(reg_base))
                return PTR_ERR(reg_base);

        disk = blk_alloc_disk(&lim, NUMA_NO_NODE);
        if (IS_ERR(disk)) {
                err = PTR_ERR(disk);
                goto out;
        }

        disk->first_minor = 0;
        disk->flags = GENHD_FL_NO_PART;
        disk->fops = &n64cart_fops;
        disk->private_data = &pdev->dev;
        strcpy(disk->disk_name, "n64cart");

        set_capacity(disk, size >> SECTOR_SHIFT);
        set_disk_ro(disk, 1);

        err = add_disk(disk);
        if (err)
                goto out_cleanup_disk;

        pr_info("n64cart: %u kb disk\n", size / 1024);

        return 0;

out_cleanup_disk:
        put_disk(disk);
out:
        return err;
}

static struct platform_driver n64cart_driver = {
        .driver = {
                .name = "n64cart",
        },
};

static int __init n64cart_init(void)
{
        return platform_driver_probe(&n64cart_driver, n64cart_probe);
}

module_init(n64cart_init);

MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
MODULE_DESCRIPTION("Driver for the N64 cart");
MODULE_LICENSE("GPL");