--- /dev/null
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for the N64 cart.
+ *
+ * Copyright (c) 2021 Lauri Kasanen
+ */
+
+#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>
+
+MODULE_AUTHOR("Lauri Kasanen <cand@gmx.com>");
+MODULE_DESCRIPTION("Driver for the N64 cart");
+MODULE_LICENSE("GPL");
+
+static unsigned int start, size;
+static u32 __iomem *reg_base;
+static struct device *dev;
+
+#define PI_DRAM_REG 0
+#define PI_CART_REG 1
+#define PI_READ_REG 2
+#define PI_WRITE_REG 3
+#define PI_STATUS_REG 4
+
+#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 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 + bv->bv_offset);
+ 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 blk_qc_t n64cart_submit_bio(struct bio *bio)
+{
+ struct bio_vec bvec;
+ u32 pos;
+ struct bvec_iter iter;
+
+ pos = bio->bi_iter.bi_sector << SECTOR_SHIFT;
+
+ bio_for_each_segment(bvec, bio, iter) {
+ if (!n64cart_do_bvec(dev, &bvec, pos))
+ goto io_error;
+ pos += bvec.bv_len;
+ }
+
+ bio_endio(bio);
+ return BLK_QC_T_NONE;
+io_error:
+ bio_io_error(bio);
+ return BLK_QC_T_NONE;
+}
+
+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)
+{
+ int err;
+ struct request_queue *queue;
+ struct gendisk *disk;
+
+ if (!start || !size) {
+ pr_err("n64cart: start and size not specified\n");
+ return -ENODEV;
+ }
+
+ if (size & 4095) {
+ pr_err("n64cart: size must be a multiple of 4K\n");
+ return -ENODEV;
+ }
+
+ queue = blk_alloc_queue(NUMA_NO_NODE);
+ if (!queue) {
+ return -ENOMEM;
+ }
+
+ reg_base = devm_platform_ioremap_resource(pdev, 0);
+ if (!reg_base) {
+ err = -EINVAL;
+ goto fail_queue;
+ }
+
+ disk = alloc_disk(0);
+ if (!disk) {
+ err = -ENOMEM;
+ goto fail_queue;
+ }
+
+ dev = &pdev->dev;
+
+ disk->first_minor = 0;
+ disk->queue = queue;
+ disk->flags = GENHD_FL_NO_PART_SCAN | GENHD_FL_EXT_DEVT;
+ disk->fops = &n64cart_fops;
+ strcpy(disk->disk_name, "n64cart");
+
+ set_capacity(disk, size / 512);
+ set_disk_ro(disk, 1);
+
+ blk_queue_flag_set(QUEUE_FLAG_NONROT, queue);
+ blk_queue_physical_block_size(queue, 4096);
+ blk_queue_logical_block_size(queue, 4096);
+
+ add_disk(disk);
+
+ pr_info("n64cart: %u kb disk\n", size / 1024);
+
+ return 0;
+fail_queue:
+ blk_cleanup_queue(queue);
+
+ 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_param(start, uint, 0);
+MODULE_PARM_DESC(start, "Start address of the cart block data");
+
+module_param(size, uint, 0);
+MODULE_PARM_DESC(size, "Size of the cart block data, in bytes");
+
+module_init(n64cart_init);
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