platform/x86: panasonic-laptop: filter out duplicate volume up/down/mute keypresses

On some Panasonic models the volume up/down/mute keypresses get
reported both through the Panasonic ACPI HKEY interface as well as
through the atkbd device.

Filter out the atkbd scan-codes for these to avoid reporting presses
twice.

Note normally we would leave the filtering of these to userspace by mapping
the scan-codes to KEY_UNKNOWN through /lib/udev/hwdb.d/60-keyboard.hwdb.
However in this case that would cause regressions since we were filtering
the Panasonic ACPI HKEY events before, so filter these in the kernel.

Fixes: ed83c917 ("platform/x86: panasonic-laptop: Resolve hotkey double trigger bug")
Reported-and-tested-by: Stefan Seyfried <seife+kernel@b1-systems.com>
Reported-and-tested-by: Kenneth Chan <kenneth.t.chan@gmail.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20220624112340.10130-7-hdegoede@redhat.com

drivers/platform/x86/Kconfig

@@ -919,6 +919,7 @@ config PANASONIC_LAPTOP
 	depends on INPUT && ACPI
 	depends on BACKLIGHT_CLASS_DEVICE
 	depends on ACPI_VIDEO=n || ACPI_VIDEO
+	depends on SERIO_I8042 || SERIO_I8042 = n
 	select INPUT_SPARSEKMAP
 	help
 	  This driver adds support for access to backlight control and hotkeys

drivers/platform/x86/panasonic-laptop.c

@@ -122,6 +122,7 @@
 #include <linux/acpi.h>
 #include <linux/backlight.h>
 #include <linux/ctype.h>
+#include <linux/i8042.h>
 #include <linux/init.h>
 #include <linux/input.h>
 #include <linux/input/sparse-keymap.h>
@@ -129,6 +130,7 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 #include <linux/seq_file.h>
+#include <linux/serio.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
@@ -241,6 +243,42 @@ struct pcc_acpi {
 	struct platform_device	*platform;
 };
 
+/*
+ * On some Panasonic models the volume up / down / mute keys send duplicate
+ * keypress events over the PS/2 kbd interface, filter these out.
+ */
+static bool panasonic_i8042_filter(unsigned char data, unsigned char str,
+				   struct serio *port)
+{
+	static bool extended;
+
+	if (str & I8042_STR_AUXDATA)
+		return false;
+
+	if (data == 0xe0) {
+		extended = true;
+		return true;
+	} else if (extended) {
+		extended = false;
+
+		switch (data & 0x7f) {
+		case 0x20: /* e0 20 / e0 a0, Volume Mute press / release */
+		case 0x2e: /* e0 2e / e0 ae, Volume Down press / release */
+		case 0x30: /* e0 30 / e0 b0, Volume Up press / release */
+			return true;
+		default:
+			/*
+			 * Report the previously filtered e0 before continuing
+			 * with the next non-filtered byte.
+			 */
+			serio_interrupt(port, 0xe0, 0);
+			return false;
+		}
+	}
+
+	return false;
+}
+
 /* method access functions */
 static int acpi_pcc_write_sset(struct pcc_acpi *pcc, int func, int val)
 {
@@ -1006,6 +1044,7 @@ static int acpi_pcc_hotkey_add(struct acpi_device *device)
 		pcc->platform = NULL;
 	}
 
+	i8042_install_filter(panasonic_i8042_filter);
 	return 0;
 
 out_platform:
@@ -1029,6 +1068,8 @@ static int acpi_pcc_hotkey_remove(struct acpi_device *device)
 	if (!device || !pcc)
 		return -EINVAL;
 
+	i8042_remove_filter(panasonic_i8042_filter);
+
 	if (pcc->platform) {
 		device_remove_file(&pcc->platform->dev, &dev_attr_cdpower);
 		platform_device_unregister(pcc->platform);