platform/x86: intel_pmc_core: export platform global reset bits via etr3 sysfs file

During PCH (platform/board) manufacturing process a global platform
reset has to be induced in order for the configuration changes take
the effect upon following platform reset. This is an internal platform
state and is not intended to be used in the regular platform resets.
The setting is exposed via ETR3 (Extended Test Mode Register 3).
After the manufacturing process is completed the register cannot be
written anymore and is hardware locked.
This setting was commonly done by accessing PMC registers via /dev/mem
but due to security concerns /dev/mem access is much more restricted,
hence the reason for exposing this setting via the dedicated sysfs
interface.
To prevent post manufacturing abuse the register is protected
by hardware locking and the file is set to read-only mode via is_visible
handler.

The register in MMIO space is defined for Cannon Lake and newer PCHs.

Cc: Hans de Goede <hdegoede@redhat.com>
Cc: David E Box <david.e.box@intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Tamar Mashiah <tamar.mashiah@intel.com>
Signed-off-by: Tomas Winkler <tomas.winkler@intel.com>
Link: https://lore.kernel.org/r/20210411141532.3004893-1-tomas.winkler@intel.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

Documentation/ABI/testing/sysfs-platform-intel-pmc

@@ -0,0 +1,20 @@
+What:		/sys/devices/platform/<platform>/etr3
+Date:		Apr 2021
+KernelVersion:	5.13
+Contact:	"Tomas Winkler" <tomas.winkler@intel.com>
+Description:
+		The file exposes "Extended Test Mode Register 3" global
+		reset bits. The bits are used during an Intel platform
+		manufacturing process to indicate that consequent reset
+		of the platform is a "global reset". This type of reset
+		is required in order for manufacturing configurations
+		to take effect.
+
+		Display global reset setting bits for PMC.
+			* bit 31 - global reset is locked
+			* bit 20 - global reset is set
+		Writing bit 20 value to the etr3 will induce
+		a platform "global reset" upon consequent platform reset,
+		in case the register is not locked.
+		The "global reset bit" should be locked on a production
+		system and the file is in read-only mode.

MAINTAINERS

@@ -9145,6 +9145,7 @@ M:	Rajneesh Bhardwaj <irenic.rajneesh@gmail.com>
 M:	David E Box <david.e.box@intel.com>
 L:	platform-driver-x86@vger.kernel.org
 S:	Maintained
+F:	Documentation/ABI/testing/sysfs-platform-intel-pmc
 F:	drivers/platform/x86/intel_pmc_core*
 
 INTEL PMIC GPIO DRIVERS

drivers/platform/x86/intel_pmc_core.c

@@ -401,6 +401,7 @@ static const struct pmc_reg_map cnp_reg_map = {
 	.pm_cfg_offset = CNP_PMC_PM_CFG_OFFSET,
 	.pm_read_disable_bit = CNP_PMC_READ_DISABLE_BIT,
 	.ltr_ignore_max = CNP_NUM_IP_IGN_ALLOWED,
+	.etr3_offset = ETR3_OFFSET,
 };
 
 static const struct pmc_reg_map icl_reg_map = {
@@ -418,6 +419,7 @@ static const struct pmc_reg_map icl_reg_map = {
 	.pm_cfg_offset = CNP_PMC_PM_CFG_OFFSET,
 	.pm_read_disable_bit = CNP_PMC_READ_DISABLE_BIT,
 	.ltr_ignore_max = ICL_NUM_IP_IGN_ALLOWED,
+	.etr3_offset = ETR3_OFFSET,
 };
 
 static const struct pmc_bit_map tgl_clocksource_status_map[] = {
@@ -585,6 +587,7 @@ static const struct pmc_reg_map tgl_reg_map = {
 	.lpm_sts = tgl_lpm_maps,
 	.lpm_status_offset = TGL_LPM_STATUS_OFFSET,
 	.lpm_live_status_offset = TGL_LPM_LIVE_STATUS_OFFSET,
+	.etr3_offset = ETR3_OFFSET,
 };
 
 static inline u32 pmc_core_reg_read(struct pmc_dev *pmcdev, int reg_offset)
@@ -603,6 +606,115 @@ static inline u64 pmc_core_adjust_slp_s0_step(struct pmc_dev *pmcdev, u32 value)
 	return (u64)value * pmcdev->map->slp_s0_res_counter_step;
 }
 
+static int set_etr3(struct pmc_dev *pmcdev)
+{
+	const struct pmc_reg_map *map = pmcdev->map;
+	u32 reg;
+	int err;
+
+	if (!map->etr3_offset)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&pmcdev->lock);
+
+	/* check if CF9 is locked */
+	reg = pmc_core_reg_read(pmcdev, map->etr3_offset);
+	if (reg & ETR3_CF9LOCK) {
+		err = -EACCES;
+		goto out_unlock;
+	}
+
+	/* write CF9 global reset bit */
+	reg |= ETR3_CF9GR;
+	pmc_core_reg_write(pmcdev, map->etr3_offset, reg);
+
+	reg = pmc_core_reg_read(pmcdev, map->etr3_offset);
+	if (!(reg & ETR3_CF9GR)) {
+		err = -EIO;
+		goto out_unlock;
+	}
+
+	err = 0;
+
+out_unlock:
+	mutex_unlock(&pmcdev->lock);
+	return err;
+}
+static umode_t etr3_is_visible(struct kobject *kobj,
+				struct attribute *attr,
+				int idx)
+{
+	struct device *dev = container_of(kobj, struct device, kobj);
+	struct pmc_dev *pmcdev = dev_get_drvdata(dev);
+	const struct pmc_reg_map *map = pmcdev->map;
+	u32 reg;
+
+	mutex_lock(&pmcdev->lock);
+	reg = pmc_core_reg_read(pmcdev, map->etr3_offset);
+	mutex_unlock(&pmcdev->lock);
+
+	return reg & ETR3_CF9LOCK ? attr->mode & (SYSFS_PREALLOC | 0444) : attr->mode;
+}
+
+static ssize_t etr3_show(struct device *dev,
+				 struct device_attribute *attr, char *buf)
+{
+	struct pmc_dev *pmcdev = dev_get_drvdata(dev);
+	const struct pmc_reg_map *map = pmcdev->map;
+	u32 reg;
+
+	if (!map->etr3_offset)
+		return -EOPNOTSUPP;
+
+	mutex_lock(&pmcdev->lock);
+
+	reg = pmc_core_reg_read(pmcdev, map->etr3_offset);
+	reg &= ETR3_CF9GR | ETR3_CF9LOCK;
+
+	mutex_unlock(&pmcdev->lock);
+
+	return sysfs_emit(buf, "0x%08x", reg);
+}
+
+static ssize_t etr3_store(struct device *dev,
+				  struct device_attribute *attr,
+				  const char *buf, size_t len)
+{
+	struct pmc_dev *pmcdev = dev_get_drvdata(dev);
+	int err;
+	u32 reg;
+
+	err = kstrtouint(buf, 16, &reg);
+	if (err)
+		return err;
+
+	/* allow only CF9 writes */
+	if (reg != ETR3_CF9GR)
+		return -EINVAL;
+
+	err = set_etr3(pmcdev);
+	if (err)
+		return err;
+
+	return len;
+}
+static DEVICE_ATTR_RW(etr3);
+
+static struct attribute *pmc_attrs[] = {
+	&dev_attr_etr3.attr,
+	NULL
+};
+
+static const struct attribute_group pmc_attr_group = {
+	.attrs = pmc_attrs,
+	.is_visible = etr3_is_visible,
+};
+
+static const struct attribute_group *pmc_dev_groups[] = {
+	&pmc_attr_group,
+	NULL
+};
+
 static int pmc_core_dev_state_get(void *data, u64 *val)
 {
 	struct pmc_dev *pmcdev = data;
@@ -1384,6 +1496,7 @@ static struct platform_driver pmc_core_driver = {
 		.name = "intel_pmc_core",
 		.acpi_match_table = ACPI_PTR(pmc_core_acpi_ids),
 		.pm = &pmc_core_pm_ops,
+		.dev_groups = pmc_dev_groups,
 	},
 	.probe = pmc_core_probe,
 	.remove = pmc_core_remove,

drivers/platform/x86/intel_pmc_core.h

@@ -200,6 +200,11 @@ enum ppfear_regs {
 #define TGL_LPM_STATUS_OFFSET			0x1C3C
 #define TGL_LPM_LIVE_STATUS_OFFSET		0x1C5C
 
+/* Extended Test Mode Register 3 (CNL and later) */
+#define ETR3_OFFSET				0x1048
+#define ETR3_CF9GR				BIT(20)
+#define ETR3_CF9LOCK				BIT(31)
+
 const char *tgl_lpm_modes[] = {
 	"S0i2.0",
 	"S0i2.1",
@@ -263,6 +268,7 @@ struct pmc_reg_map {
 	const u32 lpm_residency_offset;
 	const u32 lpm_status_offset;
 	const u32 lpm_live_status_offset;
+	const u32 etr3_offset;
 };
 
 /**