[PATCH v2] ACPI: button: Evaluate _PSB to determine power button state

[liujinlong176]

From: liujinlong <liujinlong@xxxxxxxxxx>

The ACPI button driver always synthesizes a press followed by an
immediate release upon receiving a 0x80 notify.  This prevents
userspace from determining the actual duration of a power button
press.

When the 0x80 notification is received, evaluate the _PSB control
method if present.  If _PSB returns 1, report only a key press; if
it returns 0, report only a key release.  If _PSB is not available,
fall back to the existing press+release behavior for compatibility
with firmware that does not implement it.

Signed-off-by: liujinlong <liujinlong@xxxxxxxxxx>

--- changes in v2:
 - Dropped the new ACPI notify values 0x81/0x82 per Rafael's
   feedback, as they would require an ACPI specification update.
 - Instead, evaluate the _PSB control method upon receiving the
   existing 0x80 notification to determine the real button state.
 - No longer touches include/acpi/button.h.
---
 drivers/acpi/button.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)

diff --git a/drivers/acpi/button.c b/drivers/acpi/button.c
index cdbb1023a8ee..2d079703899b 100644
--- a/drivers/acpi/button.c
+++ b/drivers/acpi/button.c
@@ -456,12 +456,25 @@ static void acpi_lid_notify(acpi_handle handle, u32 event, void *data)
 	acpi_lid_update_state(button, true);
 }
 
+static int acpi_button_evaluate_state(acpi_handle handle)
+{
+	unsigned long long state;
+	acpi_status status;
+
+	status = acpi_evaluate_integer(handle, "_PSB", NULL, &state);
+	if (ACPI_FAILURE(status))
+		return -ENODEV;
+
+	return !!state;
+}
+
 static void acpi_button_notify(acpi_handle handle, u32 event, void *data)
 {
 	struct acpi_button *button = data;
 	struct acpi_device *device = button->adev;
 	struct input_dev *input;
 	int keycode;
+	int state;
 
 	switch (event) {
 	case ACPI_BUTTON_NOTIFY_STATUS:
@@ -482,10 +495,18 @@ static void acpi_button_notify(acpi_handle handle, u32 event, void *data)
 	input = button->input;
 	keycode = test_bit(KEY_SLEEP, input->keybit) ? KEY_SLEEP : KEY_POWER;
 
-	input_report_key(input, keycode, 1);
-	input_sync(input);
-	input_report_key(input, keycode, 0);
-	input_sync(input);
+	state = acpi_button_evaluate_state(device->handle);
+	if (state < 0) {
+		/* No _PSB method, synthesize a press+release */
+		input_report_key(input, keycode, 1);
+		input_sync(input);
+		input_report_key(input, keycode, 0);
+		input_sync(input);
+	} else {
+		/* _PSB returns 1 = pressed, 0 = released */
+		input_report_key(input, keycode, state ? 1 : 0);
+		input_sync(input);
+	}
 
 	acpi_bus_generate_netlink_event(button->class, dev_name(&device->dev),
 					event, ++button->pushed);
-- 
2.25.1


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