block: Add n64 cart driver

This adds support for the Nintendo 64 console's carts. Carts are a
read-only media ranging from 8mb to 64mb.

Only one cart can be connected at once, and switching it requires a
reboot.

No module support to save RAM, as the target has 8mb RAM.

Signed-off-by: Lauri Kasanen <cand@gmx.com>
Reviewed-by: Chaitanya Kulkarni <chaitanya.kulkarni@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Acked-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

drivers/block/Kconfig

@@ -66,6 +66,12 @@ config AMIGA_Z2RAM
 	  To compile this driver as a module, choose M here: the
 	  module will be called z2ram.
 
+config N64CART
+	bool "N64 cart support"
+	depends on MACH_NINTENDO64
+	help
+	  Support for the N64 cart.
+
 config CDROM
 	tristate
 	select BLK_SCSI_REQUEST

drivers/block/Makefile

@@ -17,6 +17,7 @@ obj-$(CONFIG_PS3_DISK)		+= ps3disk.o
 obj-$(CONFIG_PS3_VRAM)		+= ps3vram.o
 obj-$(CONFIG_ATARI_FLOPPY)	+= ataflop.o
 obj-$(CONFIG_AMIGA_Z2RAM)	+= z2ram.o
+obj-$(CONFIG_N64CART)		+= n64cart.o
 obj-$(CONFIG_BLK_DEV_RAM)	+= brd.o
 obj-$(CONFIG_BLK_DEV_LOOP)	+= loop.o
 obj-$(CONFIG_XILINX_SYSACE)	+= xsysace.o

drivers/block/n64cart.c

@@ -0,0 +1,189 @@
+// 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);