[PATCH] ACPI / video: Add new hw_changes_brightness quirk, set it on PB Easynote MZ35

[Hans de Goede <hdegoede@redhat.com>]

Some machines change the brightness themselves when a brightness hotkey
gets pressed, despite us telling them not to. This causes the brightness to
go two steps up / down when the hotkey is pressed. This is esp. a problem
on older machines with only a few brightness levels.

This commit adds a new hw_changes_brightness quirk which makes
acpi_video_device_notify() only call backlight_force_update(...,
BACKLIGHT_UPDATE_HOTKEY) and not do anything else, notifying userspace that
the brightness was changed and leaving it at that fixing the dual step
problem.

BugLink: https://bugzilla.kernel.org/show_bug.cgi?id=204077
Cc: Kacper Piwiński <cosiekvfj@o2.pl>
Reported-and-tested-by: Kacper Piwiński <cosiekvfj@o2.pl>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
---
 drivers/acpi/acpi_video.c | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/acpi/acpi_video.c b/drivers/acpi/acpi_video.c
index 9489ffc06411..4f325e47519f 100644
--- a/drivers/acpi/acpi_video.c
+++ b/drivers/acpi/acpi_video.c
@@ -60,6 +60,12 @@ module_param(report_key_events, int, 0644);
 MODULE_PARM_DESC(report_key_events,
 	"0: none, 1: output changes, 2: brightness changes, 3: all");
 
+static int hw_changes_brightness = -1;
+module_param(hw_changes_brightness, int, 0644);
+MODULE_PARM_DESC(hw_changes_brightness,
+	"Set this to 1 on buggy hw which changes the brightness itself when "
+	"a hotkey is pressed: -1: auto, 0: normal 1: hw-changes-brightness");
+
 /*
  * Whether the struct acpi_video_device_attrib::device_id_scheme bit should be
  * assumed even if not actually set.
@@ -405,6 +411,14 @@ static int video_set_report_key_events(const struct dmi_system_id *id)
 	return 0;
 }
 
+static int video_hw_changes_brightness(
+	const struct dmi_system_id *d)
+{
+	if (hw_changes_brightness == -1)
+		hw_changes_brightness = 1;
+	return 0;
+}
+
 static const struct dmi_system_id video_dmi_table[] = {
 	/*
 	 * Broken _BQC workaround http://bugzilla.kernel.org/show_bug.cgi?id=13121
@@ -529,6 +543,21 @@ static const struct dmi_system_id video_dmi_table[] = {
 		DMI_MATCH(DMI_PRODUCT_NAME, "Vostro V131"),
 		},
 	},
+	/*
+	 * Some machines change the brightness themselves when a brightness
+	 * hotkey gets pressed, despite us telling them not to. In this case
+	 * acpi_video_device_notify() should only call backlight_force_update(
+	 * BACKLIGHT_UPDATE_HOTKEY) and not do anything else.
+	 */
+	{
+	 /* https://bugzilla.kernel.org/show_bug.cgi?id=204077 */
+	 .callback = video_hw_changes_brightness,
+	 .ident = "Packard Bell EasyNote MZ35",
+	 .matches = {
+		DMI_MATCH(DMI_SYS_VENDOR, "Packard Bell"),
+		DMI_MATCH(DMI_PRODUCT_NAME, "EasyNote MZ35"),
+		},
+	},
 	{}
 };
 
@@ -1612,6 +1641,14 @@ static void acpi_video_device_notify(acpi_handle handle, u32 event, void *data)
 	bus = video_device->video;
 	input = bus->input;
 
+	if (hw_changes_brightness > 0) {
+		if (video_device->backlight)
+			backlight_force_update(video_device->backlight,
+					       BACKLIGHT_UPDATE_HOTKEY);
+		acpi_notifier_call_chain(device, event, 0);
+		return;
+	}
+
 	switch (event) {
 	case ACPI_VIDEO_NOTIFY_CYCLE_BRIGHTNESS:	/* Cycle brightness */
 		brightness_switch_event(video_device, event);
-- 
2.21.0