[PATCH v9] block: Add n64 cart driver

[Lauri Kasanen <cand@gmx.com>]

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>
---
 drivers/block/Kconfig   |   6 ++
 drivers/block/Makefile  |   1 +
 drivers/block/n64cart.c | 211 ++++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 218 insertions(+)
 create mode 100644 drivers/block/n64cart.c

v9:
cosmetics
min_t

v8:
SZ_64K
remove barriers
add defines for block domain constants
__blk_mq_end_request
remove register_blkdev via GENHD_FL_EXT_DEVT
dma_alloc_noncoherent, sync

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index ecceaaa..924d768 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -72,6 +72,12 @@ 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
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index e1f6311..b9642cf 100644
--- a/drivers/block/Makefile
+++ b/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
diff --git a/drivers/block/n64cart.c b/drivers/block/n64cart.c
new file mode 100644
index 0000000..01dd008
--- /dev/null
+++ b/drivers/block/n64cart.c
@@ -0,0 +1,211 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Support for the N64 cart.
+ *
+ * Copyright (c) 2021 Lauri Kasanen
+ */
+
+#include <linux/bitops.h>
+#include <linux/blk-mq.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");
+
+#define BUFSIZE SZ_64K
+
+static unsigned int start, size;
+static struct request_queue *queue;
+static struct blk_mq_tag_set tag_set;
+static struct gendisk *disk;
+
+static void *buf;
+static dma_addr_t dma_addr;
+
+static u32 __iomem *reg_base;
+
+#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
+
+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();
+}
+
+static blk_status_t n64cart_get_seg(struct request *req)
+{
+	u32 bstart = blk_rq_pos(req) * 512;
+	u32 len = blk_rq_cur_bytes(req);
+	void *dst = bio_data(req->bio);
+
+	if (bstart + len > size)
+		return BLK_STS_IOERR;
+
+	bstart += start;
+
+	while (len) {
+		const u32 curlen = min_t(u32, len, BUFSIZE);
+
+		dma_sync_single_for_device(disk_to_dev(disk), dma_addr,
+					   BUFSIZE, DMA_FROM_DEVICE);
+
+		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, curlen - 1);
+
+		n64cart_wait_dma();
+
+		dma_sync_single_for_cpu(disk_to_dev(disk), dma_addr,
+					BUFSIZE, DMA_FROM_DEVICE);
+
+		memcpy(dst, buf, curlen);
+
+		len -= curlen;
+		dst += curlen;
+		bstart += curlen;
+	}
+
+	return BLK_STS_OK;
+}
+
+static blk_status_t n64cart_queue_rq(struct blk_mq_hw_ctx *hctx,
+				     const struct blk_mq_queue_data *bd)
+{
+	struct request *req = bd->rq;
+	blk_status_t err;
+
+	blk_mq_start_request(req);
+
+	do {
+		err = n64cart_get_seg(req);
+	} while (blk_update_request(req, err, blk_rq_cur_bytes(req)));
+
+	__blk_mq_end_request(req, BLK_STS_OK);
+	return BLK_STS_OK;
+}
+
+static const struct blk_mq_ops n64cart_mq_ops = {
+	.queue_rq = n64cart_queue_rq,
+};
+
+static const struct block_device_operations n64cart_fops = {
+	.owner		= THIS_MODULE,
+};
+
+/*
+ * 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;
+
+	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_mq_init_sq_queue(&tag_set, &n64cart_mq_ops, 1,
+				     BLK_MQ_F_SHOULD_MERGE | BLK_MQ_F_BLOCKING);
+	if (IS_ERR(queue)) {
+		return PTR_ERR(queue);
+	}
+
+	buf = dma_alloc_noncoherent(&pdev->dev, BUFSIZE, &dma_addr,
+				    DMA_FROM_DEVICE, GFP_KERNEL);
+	if (!buf) {
+		err = -ENOMEM;
+		goto fail_queue;
+	}
+
+	reg_base = devm_platform_ioremap_resource(pdev, 0);
+	if (!reg_base) {
+		err = -EINVAL;
+		goto fail_dma;
+	}
+
+	disk = alloc_disk(0);
+	if (!disk) {
+		err = -ENOMEM;
+		goto fail_dma;
+	}
+
+	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_dma:
+	dma_free_noncoherent(&pdev->dev, BUFSIZE, buf, dma_addr,
+			     DMA_FROM_DEVICE);
+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);
--
2.6.2