drm/bridge: lt9211: Add Lontium LT9211 bridge driver

Add driver for Lontium LT9211 Single/Dual-Link DSI/LVDS or Single DPI to
Single-link/Dual-Link DSI/LVDS or Single DPI bridge. This chip is highly
capable at converting formats, but sadly it is also highly undocumented.

This driver is written without any documentation from Lontium and based
only on shreds of information available in various obscure example codes,
hence long runs of unknown register patches and lengthy delays in various
places. Whichever register meaning could be divined from its behavior has
at least a comment around it.

Currently the only mode tested is Single-link DSI to Single-link LVDS.
Dual-link LVDS might work as well, the register programming is in place,
but is untested.
Reviewed-by: Robert Foss <robert.foss@linaro.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Maxime Ripard <maxime@cerno.tech>
Cc: Robert Foss <robert.foss@linaro.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
To: dri-devel@lists.freedesktop.org
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220419143958.94873-2-marex@denx.de

drivers/gpu/drm/bridge/Kconfig

@@ -100,6 +100,19 @@ config DRM_LONTIUM_LT8912B
 	  Say M here if you want to support this hardware as a module.
 	  The module will be named "lontium-lt8912b".
 
+config DRM_LONTIUM_LT9211
+	tristate "Lontium LT9211 DSI/LVDS/DPI bridge"
+	depends on OF
+	select DRM_PANEL_BRIDGE
+	select DRM_KMS_HELPER
+	select DRM_MIPI_DSI
+	select REGMAP_I2C
+	help
+	  Driver for Lontium LT9211 Single/Dual-Link DSI/LVDS or Single DPI
+	  input to Single-link/Dual-Link DSI/LVDS or Single DPI output bridge
+	  chip.
+	  Please say Y if you have such hardware.
+
 config DRM_LONTIUM_LT9611
 	tristate "Lontium LT9611 DSI/HDMI bridge"
 	select SND_SOC_HDMI_CODEC if SND_SOC

drivers/gpu/drm/bridge/Makefile

@@ -6,6 +6,7 @@ obj-$(CONFIG_DRM_CROS_EC_ANX7688) += cros-ec-anx7688.o
 obj-$(CONFIG_DRM_DISPLAY_CONNECTOR) += display-connector.o
 obj-$(CONFIG_DRM_ITE_IT6505) += ite-it6505.o
 obj-$(CONFIG_DRM_LONTIUM_LT8912B) += lontium-lt8912b.o
+obj-$(CONFIG_DRM_LONTIUM_LT9211) += lontium-lt9211.o
 obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
 obj-$(CONFIG_DRM_LONTIUM_LT9611UXC) += lontium-lt9611uxc.o
 obj-$(CONFIG_DRM_LVDS_CODEC) += lvds-codec.o