drm/mediatek: Add MT8195 Embedded DisplayPort driver

This patch adds a embedded displayport driver for the MediaTek mt8195 SoC.

It supports the MT8195, the embedded DisplayPort units. It offers
DisplayPort 1.4 with up to 4 lanes.

The driver creates a child device for the phy. The child device will
never exist without the parent being active. As they are sharing a
register range, the parent passes a regmap pointer to the child so that
both can work with the same register range. The phy driver sets device
data that is read by the parent to get the phy device that can be used
to control the phy properties.

This driver is based on an initial version by
Jitao shi <jitao.shi@mediatek.com>
Signed-off-by: Markus Schneider-Pargmann <msp@baylibre.com>
Signed-off-by: Guillaume Ranquet <granquet@baylibre.com>
Signed-off-by: Bo-Chen Chen <rex-bc.chen@mediatek.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Tested-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220901044149.16782-4-rex-bc.chen@mediatek.com

drivers/gpu/drm/mediatek/Kconfig

@@ -21,6 +21,15 @@ config DRM_MEDIATEK
 	  This driver provides kernel mode setting and
 	  buffer management to userspace.
 
+config DRM_MEDIATEK_DP
+	tristate "DRM DPTX Support for MediaTek SoCs"
+	depends on DRM_MEDIATEK
+	select PHY_MTK_DP
+	select DRM_DISPLAY_HELPER
+	select DRM_DISPLAY_DP_HELPER
+	help
+	  DRM/KMS Display Port driver for MediaTek SoCs.
+
 config DRM_MEDIATEK_HDMI
 	tristate "DRM HDMI Support for Mediatek SoCs"
 	depends on DRM_MEDIATEK

drivers/gpu/drm/mediatek/Makefile

@@ -23,3 +23,5 @@ mediatek-drm-hdmi-objs := mtk_cec.o \
 			  mtk_hdmi_ddc.o
 
 obj-$(CONFIG_DRM_MEDIATEK_HDMI) += mediatek-drm-hdmi.o
+
+obj-$(CONFIG_DRM_MEDIATEK_DP) += mtk_dp.o