platform/x86: dell-laptop: Fix keyboard max lighting for Dell Latitude E6410

This machine reports number of keyboard backlight led levels, instead of
value of the last led level index. Therefore max_brightness properly needs
to be subtracted by 1 to match led max_brightness API.

Signed-off-by: Pali Rohár <pali.rohar@gmail.com>
Reported-by: Gabriel M. Elder <gabriel@tekgnowsys.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=196913
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>

drivers/platform/x86/dell-laptop.c

@@ -37,6 +37,7 @@
 
 struct quirk_entry {
 	u8 touchpad_led;
+	u8 kbd_led_levels_off_1;
 
 	int needs_kbd_timeouts;
 	/*
@@ -67,6 +68,10 @@ static struct quirk_entry quirk_dell_xps13_9333 = {
 	.kbd_timeouts = { 0, 5, 15, 60, 5 * 60, 15 * 60, -1 },
 };
 
+static struct quirk_entry quirk_dell_latitude_e6410 = {
+	.kbd_led_levels_off_1 = 1,
+};
+
 static struct platform_driver platform_driver = {
 	.driver = {
 		.name = "dell-laptop",
@@ -269,6 +274,15 @@ static const struct dmi_system_id dell_quirks[] __initconst = {
 		},
 		.driver_data = &quirk_dell_xps13_9333,
 	},
+	{
+		.callback = dmi_matched,
+		.ident = "Dell Latitude E6410",
+		.matches = {
+			DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."),
+			DMI_MATCH(DMI_PRODUCT_NAME, "Latitude E6410"),
+		},
+		.driver_data = &quirk_dell_latitude_e6410,
+	},
 	{ }
 };
 
@@ -1149,6 +1163,9 @@ static int kbd_get_info(struct kbd_info *info)
 	units = (buffer->output[2] >> 8) & 0xFF;
 	info->levels = (buffer->output[2] >> 16) & 0xFF;
 
+	if (quirks && quirks->kbd_led_levels_off_1 && info->levels)
+		info->levels--;
+
 	if (units & BIT(0))
 		info->seconds = (buffer->output[3] >> 0) & 0xFF;
 	if (units & BIT(1))