rtc: gamecube: Add a RTC driver for the GameCube, Wii and Wii U

These three consoles share a device, the MX23L4005, which contains a
clock and 64 bytes of SRAM storage, and is exposed on the EXI bus
(similar to SPI) on channel 0, device 1.  This driver allows it to be
used as a Linux RTC device, where time can be read and set.

The hardware also exposes two timers, one which shuts down the console
and one which powers it on, but these aren’t supported currently.

On the Wii U, the counter bias is stored in a XML file, /config/rtc.xml,
encrypted in the SLC (eMMC storage), using a proprietary filesystem.  In
order to avoid having to implement all that, this driver assumes a
bootloader will parse this XML file and write the bias into the SRAM, at
the same location the other two consoles have it.
Signed-off-by: Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
Acked-by: Michael Ellerman <mpe@ellerman.id.au> (powerpc)
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20211215175501.6761-2-linkmauve@linkmauve.fr

drivers/rtc/Kconfig

@@ -1216,6 +1216,17 @@ config RTC_DRV_V3020
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-v3020.
 
+config RTC_DRV_GAMECUBE
+	tristate "Nintendo GameCube, Wii and Wii U RTC"
+	depends on GAMECUBE || WII || COMPILE_TEST
+	select REGMAP
+	help
+	  If you say yes here you will get support for the RTC subsystem
+	  of the Nintendo GameCube, Wii and Wii U.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called "rtc-gamecube".
+
 config RTC_DRV_WM831X
 	tristate "Wolfson Microelectronics WM831x RTC"
 	depends on MFD_WM831X

drivers/rtc/Makefile

@@ -111,6 +111,7 @@ obj-$(CONFIG_RTC_DRV_MT7622)	+= rtc-mt7622.o
 obj-$(CONFIG_RTC_DRV_MV)	+= rtc-mv.o
 obj-$(CONFIG_RTC_DRV_MXC)	+= rtc-mxc.o
 obj-$(CONFIG_RTC_DRV_MXC_V2)	+= rtc-mxc_v2.o
+obj-$(CONFIG_RTC_DRV_GAMECUBE)	+= rtc-gamecube.o
 obj-$(CONFIG_RTC_DRV_NTXEC)	+= rtc-ntxec.o
 obj-$(CONFIG_RTC_DRV_OMAP)	+= rtc-omap.o
 obj-$(CONFIG_RTC_DRV_OPAL)	+= rtc-opal.o

drivers/rtc/rtc-gamecube.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Nintendo GameCube, Wii and Wii U RTC driver
+ *
+ * This driver is for the MX23L4005, more specifically its real-time clock and
+ * SRAM storage.  The value returned by the RTC counter must be added with the
+ * offset stored in a bias register in SRAM (on the GameCube and Wii) or in
+ * /config/rtc.xml (on the Wii U).  The latter being very impractical to access
+ * from Linux, this driver assumes the bootloader has read it and stored it in
+ * SRAM like for the other two consoles.
+ *
+ * This device sits on a bus named EXI (which is similar to SPI), channel 0,
+ * device 1.  This driver assumes no other user of the EXI bus, which is
+ * currently the case but would have to be reworked to add support for other
+ * GameCube hardware exposed on this bus.
+ *
+ * References:
+ * - https://wiiubrew.org/wiki/Hardware/RTC
+ * - https://wiibrew.org/wiki/MX23L4005
+ *
+ * Copyright (C) 2018 rw-r-r-0644
+ * Copyright (C) 2021 Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>
+ *
+ * Based on rtc-gcn.c
+ * Copyright (C) 2004-2009 The GameCube Linux Team
+ * Copyright (C) 2005,2008,2009 Albert Herranz
+ * Based on gamecube_time.c from Torben Nielsen.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/of_address.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/rtc.h>
+#include <linux/time.h>
+
+/* EXI registers */
+#define EXICSR	0
+#define EXICR	12
+#define EXIDATA	16
+
+/* EXI register values */
+#define EXICSR_DEV		0x380
+	#define EXICSR_DEV1	0x100
+#define EXICSR_CLK		0x070
+	#define EXICSR_CLK_1MHZ	0x000
+	#define EXICSR_CLK_2MHZ	0x010
+	#define EXICSR_CLK_4MHZ	0x020
+	#define EXICSR_CLK_8MHZ	0x030
+	#define EXICSR_CLK_16MHZ 0x040
+	#define EXICSR_CLK_32MHZ 0x050
+#define EXICSR_INT		0x008
+	#define EXICSR_INTSET	0x008
+
+#define EXICR_TSTART		0x001
+#define EXICR_TRSMODE		0x002
+	#define EXICR_TRSMODE_IMM 0x000
+#define EXICR_TRSTYPE		0x00C
+	#define EXICR_TRSTYPE_R	0x000
+	#define EXICR_TRSTYPE_W	0x004
+#define EXICR_TLEN		0x030
+	#define EXICR_TLEN32	0x030
+
+/* EXI registers values to access the RTC */
+#define RTC_EXICSR	(EXICSR_DEV1 | EXICSR_CLK_8MHZ | EXICSR_INTSET)
+#define RTC_EXICR_W	(EXICR_TSTART | EXICR_TRSMODE_IMM | EXICR_TRSTYPE_W | EXICR_TLEN32)
+#define RTC_EXICR_R	(EXICR_TSTART | EXICR_TRSMODE_IMM | EXICR_TRSTYPE_R | EXICR_TLEN32)
+#define RTC_EXIDATA_W	0x80000000
+
+/* RTC registers */
+#define RTC_COUNTER	0x200000
+#define RTC_SRAM	0x200001
+#define RTC_SRAM_BIAS	0x200004
+#define RTC_SNAPSHOT	0x204000
+#define RTC_ONTMR	0x210000
+#define RTC_OFFTMR	0x210001
+#define RTC_TEST0	0x210004
+#define RTC_TEST1	0x210005
+#define RTC_TEST2	0x210006
+#define RTC_TEST3	0x210007
+#define RTC_CONTROL0	0x21000c
+#define RTC_CONTROL1	0x21000d
+
+struct priv {
+	struct regmap *regmap;
+	void __iomem *iob;
+	u32 rtc_bias;
+};
+
+static int exi_read(void *context, u32 reg, u32 *data)
+{
+	struct priv *d = (struct priv *)context;
+	void __iomem *iob = d->iob;
+
+	/* The spin loops here loop about 15~16 times each, so there is no need
+	 * to use a more expensive sleep method.
+	 */
+
+	/* Write register offset */
+	iowrite32be(RTC_EXICSR, iob + EXICSR);
+	iowrite32be(reg << 8, iob + EXIDATA);
+	iowrite32be(RTC_EXICR_W, iob + EXICR);
+	while (!(ioread32be(iob + EXICSR) & EXICSR_INTSET))
+		cpu_relax();
+
+	/* Read data */
+	iowrite32be(RTC_EXICSR, iob + EXICSR);
+	iowrite32be(RTC_EXICR_R, iob + EXICR);
+	while (!(ioread32be(iob + EXICSR) & EXICSR_INTSET))
+		cpu_relax();
+	*data = ioread32be(iob + EXIDATA);
+
+	/* Clear channel parameters */
+	iowrite32be(0, iob + EXICSR);
+
+	return 0;
+}
+
+static int exi_write(void *context, u32 reg, u32 data)
+{
+	struct priv *d = (struct priv *)context;
+	void __iomem *iob = d->iob;
+
+	/* The spin loops here loop about 15~16 times each, so there is no need
+	 * to use a more expensive sleep method.
+	 */
+
+	/* Write register offset */
+	iowrite32be(RTC_EXICSR, iob + EXICSR);
+	iowrite32be(RTC_EXIDATA_W | (reg << 8), iob + EXIDATA);
+	iowrite32be(RTC_EXICR_W, iob + EXICR);
+	while (!(ioread32be(iob + EXICSR) & EXICSR_INTSET))
+		cpu_relax();
+
+	/* Write data */
+	iowrite32be(RTC_EXICSR, iob + EXICSR);
+	iowrite32be(data, iob + EXIDATA);
+	iowrite32be(RTC_EXICR_W, iob + EXICR);
+	while (!(ioread32be(iob + EXICSR) & EXICSR_INTSET))
+		cpu_relax();
+
+	/* Clear channel parameters */
+	iowrite32be(0, iob + EXICSR);
+
+	return 0;
+}
+
+static const struct regmap_bus exi_bus = {
+	/* TODO: is that true?  Not that it matters here, but still. */
+	.fast_io = true,
+	.reg_read = exi_read,
+	.reg_write = exi_write,
+};
+
+static int gamecube_rtc_read_time(struct device *dev, struct rtc_time *t)
+{
+	struct priv *d = dev_get_drvdata(dev);
+	int ret;
+	u32 counter;
+	time64_t timestamp;
+
+	ret = regmap_read(d->regmap, RTC_COUNTER, &counter);
+	if (ret)
+		return ret;
+
+	/* Add the counter and the bias to obtain the timestamp */
+	timestamp = (time64_t)d->rtc_bias + counter;
+	rtc_time64_to_tm(timestamp, t);
+
+	return 0;
+}
+
+static int gamecube_rtc_set_time(struct device *dev, struct rtc_time *t)
+{
+	struct priv *d = dev_get_drvdata(dev);
+	time64_t timestamp;
+
+	/* Subtract the timestamp and the bias to obtain the counter value */
+	timestamp = rtc_tm_to_time64(t);
+	return regmap_write(d->regmap, RTC_COUNTER, timestamp - d->rtc_bias);
+}
+
+static const struct rtc_class_ops gamecube_rtc_ops = {
+	.read_time	= gamecube_rtc_read_time,
+	.set_time	= gamecube_rtc_set_time,
+};
+
+static int gamecube_rtc_read_offset_from_sram(struct priv *d)
+{
+	struct device_node *np;
+	int ret;
+	struct resource res;
+	void __iomem *hw_srnprot;
+	u32 old;
+
+	np = of_find_compatible_node(NULL, NULL, "nintendo,latte-srnprot");
+	if (!np)
+		np = of_find_compatible_node(NULL, NULL,
+					     "nintendo,hollywood-srnprot");
+	if (!np) {
+		pr_info("HW_SRNPROT not found, assuming a GameCube\n");
+		return regmap_read(d->regmap, RTC_SRAM_BIAS, &d->rtc_bias);
+	}
+
+	ret = of_address_to_resource(np, 0, &res);
+	if (ret) {
+		pr_err("no io memory range found\n");
+		return -1;
+	}
+
+	hw_srnprot = ioremap(res.start, resource_size(&res));
+	old = ioread32be(hw_srnprot);
+
+	/* TODO: figure out why we use this magic constant.  I obtained it by
+	 * reading the leftover value after boot, after IOSU already ran.
+	 *
+	 * On my Wii U, setting this register to 1 prevents the console from
+	 * rebooting properly, so wiiubrew.org must be missing something.
+	 *
+	 * See https://wiiubrew.org/wiki/Hardware/Latte_registers
+	 */
+	if (old != 0x7bf)
+		iowrite32be(0x7bf, hw_srnprot);
+
+	/* Get the offset from RTC SRAM.
+	 *
+	 * Its default location on the GameCube and on the Wii is in the SRAM,
+	 * while on the Wii U the bootloader needs to fill it with the contents
+	 * of /config/rtc.xml on the SLC (the eMMC).  We don’t do that from
+	 * Linux since it requires implementing a proprietary filesystem and do
+	 * file decryption, instead we require the bootloader to fill the same
+	 * SRAM address as on previous consoles.
+	 */
+	ret = regmap_read(d->regmap, RTC_SRAM_BIAS, &d->rtc_bias);
+	if (ret) {
+		pr_err("failed to get the RTC bias\n");
+		return -1;
+	}
+
+	/* Reset SRAM access to how it was before, our job here is done. */
+	if (old != 0x7bf)
+		iowrite32be(old, hw_srnprot);
+	iounmap(hw_srnprot);
+
+	return 0;
+}
+
+static const struct regmap_range rtc_rd_ranges[] = {
+	regmap_reg_range(0x200000, 0x200010),
+	regmap_reg_range(0x204000, 0x204000),
+	regmap_reg_range(0x210000, 0x210001),
+	regmap_reg_range(0x210004, 0x210007),
+	regmap_reg_range(0x21000c, 0x21000d),
+};
+
+static const struct regmap_access_table rtc_rd_regs = {
+	.yes_ranges =	rtc_rd_ranges,
+	.n_yes_ranges =	ARRAY_SIZE(rtc_rd_ranges),
+};
+
+static const struct regmap_range rtc_wr_ranges[] = {
+	regmap_reg_range(0x200000, 0x200010),
+	regmap_reg_range(0x204000, 0x204000),
+	regmap_reg_range(0x210000, 0x210001),
+	regmap_reg_range(0x21000d, 0x21000d),
+};
+
+static const struct regmap_access_table rtc_wr_regs = {
+	.yes_ranges =	rtc_wr_ranges,
+	.n_yes_ranges =	ARRAY_SIZE(rtc_wr_ranges),
+};
+
+static const struct regmap_config gamecube_rtc_regmap_config = {
+	.reg_bits = 24,
+	.val_bits = 32,
+	.rd_table = &rtc_rd_regs,
+	.wr_table = &rtc_wr_regs,
+	.max_register = 0x21000d,
+	.name = "gamecube-rtc",
+};
+
+static int gamecube_rtc_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct rtc_device *rtc;
+	struct priv *d;
+	int ret;
+
+	d = devm_kzalloc(dev, sizeof(struct priv), GFP_KERNEL);
+	if (IS_ERR(d))
+		return PTR_ERR(d);
+
+	d->iob = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(d->iob))
+		return PTR_ERR(d->iob);
+
+	d->regmap = devm_regmap_init(dev, &exi_bus, d,
+				     &gamecube_rtc_regmap_config);
+	if (IS_ERR(d->regmap))
+		return PTR_ERR(d->regmap);
+
+	ret = gamecube_rtc_read_offset_from_sram(d);
+	if (ret)
+		return ret;
+	dev_dbg(dev, "SRAM bias: 0x%x", d->rtc_bias);
+
+	dev_set_drvdata(dev, d);
+
+	rtc = devm_rtc_allocate_device(dev);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	/* We can represent further than that, but it depends on the stored
+	 * bias and we can’t modify it persistently on all supported consoles,
+	 * so here we pretend to be limited to 2106.
+	 */
+	rtc->range_min = 0;
+	rtc->range_max = U32_MAX;
+	rtc->ops = &gamecube_rtc_ops;
+
+	devm_rtc_register_device(rtc);
+
+	return 0;
+}
+
+static const struct of_device_id gamecube_rtc_of_match[] = {
+	{.compatible = "nintendo,latte-exi" },
+	{.compatible = "nintendo,hollywood-exi" },
+	{.compatible = "nintendo,flipper-exi" },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, gamecube_rtc_of_match);
+
+static struct platform_driver gamecube_rtc_driver = {
+	.probe		= gamecube_rtc_probe,
+	.driver		= {
+		.name	= "rtc-gamecube",
+		.of_match_table	= gamecube_rtc_of_match,
+	},
+};
+module_platform_driver(gamecube_rtc_driver);
+
+MODULE_AUTHOR("Emmanuel Gil Peyrot <linkmauve@linkmauve.fr>");
+MODULE_DESCRIPTION("Nintendo GameCube, Wii and Wii U RTC driver");
+MODULE_LICENSE("GPL");