ACPI / bus: Introduce a list of ids for "always present" devices

Several Bay / Cherry Trail devices (all of which ship with Windows 10) hide
the LPSS PWM controller in ACPI, typically the _STA method looks like this:

    Method (_STA, 0, NotSerialized)  // _STA: Status
    {
        If (OSID == One)
        {
            Return (Zero)
        }

        Return (0x0F)
    }

Where OSID is some dark magic seen in all Cherry Trail ACPI tables making
the machine behave differently depending on which OS it *thinks* it is
booting, this gets set in a number of ways which we cannot control, on
some newer machines it simple hardcoded to "One" aka win10.

This causes the PWM controller to get hidden, which means Linux cannot
control the backlight level on cht based tablets / laptops.

Since loading the driver for this does no harm (the only in kernel user
of it is the i915 driver, which will only uses it when it needs it), this
commit makes acpi_bus_get_status() always set status to ACPI_STA_DEFAULT
for the LPSS PWM device, fixing the lack of backlight control.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
[ rjw: Rename the new file to utils.c ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/Makefile

@@ -50,6 +50,7 @@ acpi-$(CONFIG_ACPI_REDUCED_HARDWARE_ONLY) += evged.o
 acpi-y				+= sysfs.o
 acpi-y				+= property.o
 acpi-$(CONFIG_X86)		+= acpi_cmos_rtc.o
+acpi-$(CONFIG_X86)		+= x86/utils.o
 acpi-$(CONFIG_DEBUG_FS)		+= debugfs.o
 acpi-$(CONFIG_ACPI_NUMA)	+= numa.o
 acpi-$(CONFIG_ACPI_PROCFS_POWER) += cm_sbs.o

drivers/acpi/bus.c

@@ -114,6 +114,11 @@ int acpi_bus_get_status(struct acpi_device *device)
 	acpi_status status;
 	unsigned long long sta;
 
+	if (acpi_device_always_present(device)) {
+		acpi_set_device_status(device, ACPI_STA_DEFAULT);
+		return 0;
+	}
+
 	status = acpi_bus_get_status_handle(device->handle, &sta);
 	if (ACPI_FAILURE(status))
 		return -ENODEV;

drivers/acpi/x86/utils.c

+/*
+ * X86 ACPI Utility Functions
+ *
+ * Copyright (C) 2017 Hans de Goede <hdegoede@redhat.com>
+ *
+ * Based on various non upstream patches to support the CHT Whiskey Cove PMIC:
+ * Copyright (C) 2013-2015 Intel Corporation. All rights reserved.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/acpi.h>
+#include <asm/cpu_device_id.h>
+#include <asm/intel-family.h>
+#include "../internal.h"
+
+/*
+ * Some ACPI devices are hidden (status == 0x0) in recent BIOS-es because
+ * some recent Windows drivers bind to one device but poke at multiple
+ * devices at the same time, so the others get hidden.
+ * We work around this by always reporting ACPI_STA_DEFAULT for these
+ * devices. Note this MUST only be done for devices where this is safe.
+ *
+ * This forcing of devices to be present is limited to specific CPU (SoC)
+ * models both to avoid potentially causing trouble on other models and
+ * because some HIDs are re-used on different SoCs for completely
+ * different devices.
+ */
+struct always_present_id {
+	struct acpi_device_id hid[2];
+	struct x86_cpu_id cpu_ids[2];
+	const char *uid;
+};
+
+#define ICPU(model)	{ X86_VENDOR_INTEL, 6, model, X86_FEATURE_ANY, }
+
+#define ENTRY(hid, uid, cpu_models) {					\
+	{ { hid, }, {} },						\
+	{ cpu_models, {} },						\
+	uid,								\
+}
+
+static const struct always_present_id always_present_ids[] = {
+	/*
+	 * Bay / Cherry Trail PWM directly poked by GPU driver in win10,
+	 * but Linux uses a separate PWM driver, harmless if not used.
+	 */
+	ENTRY("80860F09", "1", ICPU(INTEL_FAM6_ATOM_SILVERMONT1)),
+	ENTRY("80862288", "1", ICPU(INTEL_FAM6_ATOM_AIRMONT)),
+};
+
+bool acpi_device_always_present(struct acpi_device *adev)
+{
+	u32 *status = (u32 *)&adev->status;
+	u32 old_status = *status;
+	bool ret = false;
+	unsigned int i;
+
+	/* acpi_match_device_ids checks status, so set it to default */
+	*status = ACPI_STA_DEFAULT;
+	for (i = 0; i < ARRAY_SIZE(always_present_ids); i++) {
+		if (acpi_match_device_ids(adev, always_present_ids[i].hid))
+			continue;
+
+		if (!adev->pnp.unique_id ||
+		    strcmp(adev->pnp.unique_id, always_present_ids[i].uid))
+			continue;
+
+		if (!x86_match_cpu(always_present_ids[i].cpu_ids))
+			continue;
+
+		if (old_status != ACPI_STA_DEFAULT) /* Log only once */
+			dev_info(&adev->dev,
+				 "Device [%s] is in always present list\n",
+				 adev->pnp.bus_id);
+
+		ret = true;
+		break;
+	}
+	*status = old_status;
+
+	return ret;
+}

include/acpi/acpi_bus.h

@@ -586,6 +586,15 @@ struct acpi_pci_root *acpi_pci_find_root(acpi_handle handle);
 int acpi_enable_wakeup_device_power(struct acpi_device *dev, int state);
 int acpi_disable_wakeup_device_power(struct acpi_device *dev);
 
+#ifdef CONFIG_X86
+bool acpi_device_always_present(struct acpi_device *adev);
+#else
+static inline bool acpi_device_always_present(struct acpi_device *adev)
+{
+	return false;
+}
+#endif
+
 #ifdef CONFIG_PM
 acpi_status acpi_add_pm_notifier(struct acpi_device *adev, struct device *dev,
 				 void (*work_func)(struct work_struct *work));