platform/x86: Add intel_bytcrc_pwrsrc driver

Add a new driver for the power-, wake- and reset-source functionality
of the Bay Trail (BYT) version of the Crystal Cove PMIC.

The main functionality here is detecting which power-sources (USB /
DC in / battery) are active. This is normally exposed to userspace as
a power_supply class charger device with an online sysfs attribute.

But if a charger is online or not is already exposed on BYT-CRC devices
through either an ACPI AC power_supply device, or through a native driver
for the battery charger chip (e.g. a BQ24292i).

So instead of adding duplicate info under the power_supply class this
driver exports the info through debugfs and likewise adds debugfs files
for the reset- and wake-source info / registers.

Despite this driver only exporting debugfs bits it is still useful to
have this driver because it clears the wake- and reset-source registers
after reading them. Not clearing these can have undesirable side-effects.

Specifically if the WAKESRC register contains 0x01 (wake by powerbutton)
on reboot then the firmware on some tablets turns the reboot into
a poweroff. I guess this may be necessary to make long power-presses turn
into a poweroff somehow?
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20230303221928.285477-1-hdegoede@redhat.com

drivers/platform/x86/intel/Kconfig

@@ -80,6 +80,16 @@ config INTEL_BXTWC_PMIC_TMU
 	  This driver enables the alarm wakeup functionality in the TMU unit of
 	  Whiskey Cove PMIC.
 
+config INTEL_BYTCRC_PWRSRC
+	tristate "Intel Bay Trail Crystal Cove power source driver"
+	depends on INTEL_SOC_PMIC
+	help
+	  This option adds a power source driver for Crystal Cove PMICs
+	  on Intel Bay Trail devices.
+
+	  To compile this driver as a module, choose M here: the module
+	  will be called intel_bytcrc_pwrsrc.
+
 config INTEL_CHTDC_TI_PWRBTN
 	tristate "Intel Cherry Trail Dollar Cove TI power button driver"
 	depends on INTEL_SOC_PMIC_CHTDC_TI

drivers/platform/x86/intel/Makefile

@@ -38,6 +38,8 @@ intel_bxtwc_tmu-y			:= bxtwc_tmu.o
 obj-$(CONFIG_INTEL_BXTWC_PMIC_TMU)	+= intel_bxtwc_tmu.o
 intel_crystal_cove_charger-y		:= crystal_cove_charger.o
 obj-$(CONFIG_X86_ANDROID_TABLETS)	+= intel_crystal_cove_charger.o
+intel_bytcrc_pwrsrc-y			:= bytcrc_pwrsrc.o
+obj-$(CONFIG_INTEL_BYTCRC_PWRSRC)	+= intel_bytcrc_pwrsrc.o
 intel_chtdc_ti_pwrbtn-y			:= chtdc_ti_pwrbtn.o
 obj-$(CONFIG_INTEL_CHTDC_TI_PWRBTN)	+= intel_chtdc_ti_pwrbtn.o
 intel_chtwc_int33fe-y			:= chtwc_int33fe.o

drivers/platform/x86/intel/bytcrc_pwrsrc.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Power-source driver for Bay Trail Crystal Cove PMIC
+ *
+ * Copyright (c) 2023 Hans de Goede <hdegoede@redhat.com>
+ *
+ * Based on intel_crystalcove_pwrsrc.c from Android kernel sources, which is:
+ * Copyright (C) 2013 Intel Corporation
+ */
+
+#include <linux/debugfs.h>
+#include <linux/mfd/intel_soc_pmic.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define CRYSTALCOVE_SPWRSRC_REG		0x1E
+#define CRYSTALCOVE_RESETSRC0_REG	0x20
+#define CRYSTALCOVE_RESETSRC1_REG	0x21
+#define CRYSTALCOVE_WAKESRC_REG		0x22
+
+struct crc_pwrsrc_data {
+	struct regmap *regmap;
+	struct dentry *debug_dentry;
+	unsigned int resetsrc0;
+	unsigned int resetsrc1;
+	unsigned int wakesrc;
+};
+
+static const char * const pwrsrc_pwrsrc_info[] = {
+	/* bit 0 */ "USB",
+	/* bit 1 */ "DC in",
+	/* bit 2 */ "Battery",
+	NULL,
+};
+
+static const char * const pwrsrc_resetsrc0_info[] = {
+	/* bit 0 */ "SOC reporting a thermal event",
+	/* bit 1 */ "critical PMIC temperature",
+	/* bit 2 */ "critical system temperature",
+	/* bit 3 */ "critical battery temperature",
+	/* bit 4 */ "VSYS under voltage",
+	/* bit 5 */ "VSYS over voltage",
+	/* bit 6 */ "battery removal",
+	NULL,
+};
+
+static const char * const pwrsrc_resetsrc1_info[] = {
+	/* bit 0 */ "VCRIT threshold",
+	/* bit 1 */ "BATID reporting battery removal",
+	/* bit 2 */ "user pressing the power button",
+	NULL,
+};
+
+static const char * const pwrsrc_wakesrc_info[] = {
+	/* bit 0 */ "user pressing the power button",
+	/* bit 1 */ "a battery insertion",
+	/* bit 2 */ "a USB charger insertion",
+	/* bit 3 */ "an adapter insertion",
+	NULL,
+};
+
+static void crc_pwrsrc_log(struct seq_file *seq, const char *prefix,
+			   const char * const *info, unsigned int reg_val)
+{
+	int i;
+
+	for (i = 0; info[i]; i++) {
+		if (reg_val & BIT(i))
+			seq_printf(seq, "%s by %s\n", prefix, info[i]);
+	}
+}
+
+static int pwrsrc_show(struct seq_file *seq, void *unused)
+{
+	struct crc_pwrsrc_data *data = seq->private;
+	unsigned int reg_val;
+	int ret;
+
+	ret = regmap_read(data->regmap, CRYSTALCOVE_SPWRSRC_REG, &reg_val);
+	if (ret)
+		return ret;
+
+	crc_pwrsrc_log(seq, "System powered", pwrsrc_pwrsrc_info, reg_val);
+	return 0;
+}
+
+static int resetsrc_show(struct seq_file *seq, void *unused)
+{
+	struct crc_pwrsrc_data *data = seq->private;
+
+	crc_pwrsrc_log(seq, "Last shutdown caused", pwrsrc_resetsrc0_info, data->resetsrc0);
+	crc_pwrsrc_log(seq, "Last shutdown caused", pwrsrc_resetsrc1_info, data->resetsrc1);
+	return 0;
+}
+
+static int wakesrc_show(struct seq_file *seq, void *unused)
+{
+	struct crc_pwrsrc_data *data = seq->private;
+
+	crc_pwrsrc_log(seq, "Last wake caused", pwrsrc_wakesrc_info, data->wakesrc);
+	return 0;
+}
+
+DEFINE_SHOW_ATTRIBUTE(pwrsrc);
+DEFINE_SHOW_ATTRIBUTE(resetsrc);
+DEFINE_SHOW_ATTRIBUTE(wakesrc);
+
+static int crc_pwrsrc_read_and_clear(struct crc_pwrsrc_data *data,
+				     unsigned int reg, unsigned int *val)
+{
+	int ret;
+
+	ret = regmap_read(data->regmap, reg, val);
+	if (ret)
+		return ret;
+
+	return regmap_write(data->regmap, reg, *val);
+}
+
+static int crc_pwrsrc_probe(struct platform_device *pdev)
+{
+	struct intel_soc_pmic *pmic = dev_get_drvdata(pdev->dev.parent);
+	struct crc_pwrsrc_data *data;
+	int ret;
+
+	data = devm_kzalloc(&pdev->dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->regmap = pmic->regmap;
+
+	/*
+	 * Read + clear resetsrc0/1 and wakesrc now, so that they get
+	 * cleared even if the debugfs interface is never used.
+	 *
+	 * Properly clearing the wakesrc is important, leaving bit 0 of it
+	 * set turns reboot into poweroff on some tablets.
+	 */
+	ret = crc_pwrsrc_read_and_clear(data, CRYSTALCOVE_RESETSRC0_REG, &data->resetsrc0);
+	if (ret)
+		return ret;
+
+	ret = crc_pwrsrc_read_and_clear(data, CRYSTALCOVE_RESETSRC1_REG, &data->resetsrc1);
+	if (ret)
+		return ret;
+
+	ret = crc_pwrsrc_read_and_clear(data, CRYSTALCOVE_WAKESRC_REG, &data->wakesrc);
+	if (ret)
+		return ret;
+
+	data->debug_dentry = debugfs_create_dir(KBUILD_MODNAME, NULL);
+	debugfs_create_file("pwrsrc", 0444, data->debug_dentry, data, &pwrsrc_fops);
+	debugfs_create_file("resetsrc", 0444, data->debug_dentry, data, &resetsrc_fops);
+	debugfs_create_file("wakesrc", 0444, data->debug_dentry, data, &wakesrc_fops);
+
+	platform_set_drvdata(pdev, data);
+	return 0;
+}
+
+static int crc_pwrsrc_remove(struct platform_device *pdev)
+{
+	struct crc_pwrsrc_data *data = platform_get_drvdata(pdev);
+
+	debugfs_remove_recursive(data->debug_dentry);
+	return 0;
+}
+
+static struct platform_driver crc_pwrsrc_driver = {
+	.probe = crc_pwrsrc_probe,
+	.remove = crc_pwrsrc_remove,
+	.driver = {
+		.name = "crystal_cove_pwrsrc",
+	},
+};
+module_platform_driver(crc_pwrsrc_driver);
+
+MODULE_ALIAS("platform:crystal_cove_pwrsrc");
+MODULE_AUTHOR("Hans de Goede <hdegoede@redhat.com>");
+MODULE_DESCRIPTION("Power-source driver for Bay Trail Crystal Cove PMIC");
+MODULE_LICENSE("GPL");