arm64: dts: mediatek: mt8173-elm-hana: Add vdd-supply to second source trackpad

[ Upstream commit f766fae ]

The Hana device has a second source option trackpad, but it is missing
its regulator supply. It only works because the regulator is marked as
always-on.

Add the regulator supply, but leave out the post-power-on delay. Instead,
document the post-power-on delay along with the reason for not adding
it in a comment.

Fixes: 689b937 ("arm64: dts: mediatek: add mt8173 elm and hana board")
Signed-off-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20241018082001.1296963-1-wenst@chromium.org
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>

Author: wens

arch/arm64/boot/dts/mediatek/mt8173-elm-hana.dtsi

@@ -49,6 +49,14 @@
 		interrupts-extended = <&pio 117 IRQ_TYPE_LEVEL_LOW>;
 		reg = <0x2c>;
 		hid-descr-addr = <0x0020>;
+		/*
+		 * The trackpad needs a post-power-on delay of 100ms,
+		 * but at time of writing, the power supply for it on
+		 * this board is always on. The delay is therefore not
+		 * added to avoid impacting the readiness of the
+		 * trackpad.
+		 */
+		vdd-supply = <&mt6397_vgp6_reg>;
 		wakeup-source;
 	};
 };