drm/display: Introduce a DRM display-helper module

Replace the DP-helper module with a display-helper module. The
support for DisplayPort becomes an internal option that drivers
have to select. Update all related Kconfig and Makefile rules.

Besides the existing code for DisplayPort, the new module will
contain helpers for other video-output standards, such as HDMI.
Drivers will have to select their required video-output helpers.

Linking all display-related code into a single module avoids the
proliferation of small kernel modules.

The module parameters drm_dp_cec_unregister_delay, dp_aux_i2c_speed_khz,
and dp_aux_i2c_transfer_size are moving from the drm_dp_helper namespace
to drm_display_helper.

v2:
	* mention module parameters in commit message (Javier)
	* distiguish between display module and DP support in Kconfig
	* update Makefile rules for DP helpers
	* move Kconfig rules into separate file under display/

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220421073108.19226-4-tzimmermann@suse.de

4 files changed, 49 insertions, 9 deletions

diff --git a/drivers/gpu/drm/display/Kconfig b/drivers/gpu/drm/display/Kconfig
new file mode 100644
index 000000000000..fcd9ffd39f26
--- /dev/null
+++ b/drivers/gpu/drm/display/Kconfig
@@ -0,0 +1,37 @@
+# SPDX-License-Identifier: MIT
+
+config DRM_DP_AUX_BUS
+	tristate
+	depends on DRM
+	depends on OF
+
+config DRM_DISPLAY_HELPER
+	tristate
+	depends on DRM
+	help
+	  DRM helpers for display adapters.
+
+config DRM_DISPLAY_DP_HELPER
+	bool
+	depends on DRM_DISPLAY_HELPER
+	help
+	  DRM display helpers for DisplayPort.
+
+config DRM_DP_AUX_CHARDEV
+	bool "DRM DP AUX Interface"
+	depends on DRM
+	help
+	  Choose this option to enable a /dev/drm_dp_auxN node that allows to
+	  read and write values to arbitrary DPCD registers on the DP aux
+	  channel.
+
+config DRM_DP_CEC
+	bool "Enable DisplayPort CEC-Tunneling-over-AUX HDMI support"
+	depends on DRM
+	select CEC_CORE
+	help
+	  Choose this option if you want to enable HDMI CEC support for
+	  DisplayPort/USB-C to HDMI adapters.
+
+	  Note: not all adapters support this feature, and even for those
+	  that do support this they often do not hook up the CEC pin.
diff --git a/drivers/gpu/drm/display/Makefile b/drivers/gpu/drm/display/Makefile
index 75faffc706b1..99ba6750a315 100644
--- a/drivers/gpu/drm/display/Makefile
+++ b/drivers/gpu/drm/display/Makefile
@@ -2,8 +2,11 @@
 
 obj-$(CONFIG_DRM_DP_AUX_BUS) += drm_dp_aux_bus.o
 
-drm_dp_helper-y := drm_dp.o drm_dp_dual_mode_helper.o drm_dp_helper_mod.o drm_dp_mst_topology.o
-drm_dp_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
-drm_dp_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
+drm_display_helper-y := drm_display_helper_mod.o
+drm_display_helper-$(CONFIG_DRM_DISPLAY_DP_HELPER) += drm_dp_dual_mode_helper.o \
+						      drm_dp_helper.o \
+						      drm_dp_mst_topology.o
+drm_display_helper-$(CONFIG_DRM_DP_AUX_CHARDEV) += drm_dp_aux_dev.o
+drm_display_helper-$(CONFIG_DRM_DP_CEC) += drm_dp_cec.o
 
-obj-$(CONFIG_DRM_DP_HELPER) += drm_dp_helper.o
+obj-$(CONFIG_DRM_DISPLAY_HELPER) += drm_display_helper.o
diff --git a/drivers/gpu/drm/display/drm_dp_helper_mod.c b/drivers/gpu/drm/display/drm_display_helper_mod.c
index db753de24000..d8a6e6228773 100644
--- a/drivers/gpu/drm/display/drm_dp_helper_mod.c
+++ b/drivers/gpu/drm/display/drm_display_helper_mod.c
@@ -4,19 +4,19 @@
 
 #include "drm_dp_helper_internal.h"
 
-MODULE_DESCRIPTION("DRM DisplayPort helper");
+MODULE_DESCRIPTION("DRM display adapter helper");
 MODULE_LICENSE("GPL and additional rights");
 
-static int __init drm_dp_helper_module_init(void)
+static int __init drm_display_helper_module_init(void)
 {
 	return drm_dp_aux_dev_init();
 }
 
-static void __exit drm_dp_helper_module_exit(void)
+static void __exit drm_display_helper_module_exit(void)
 {
 	/* Call exit functions from specific dp helpers here */
 	drm_dp_aux_dev_exit();
 }
 
-module_init(drm_dp_helper_module_init);
-module_exit(drm_dp_helper_module_exit);
+module_init(drm_display_helper_module_init);
+module_exit(drm_display_helper_module_exit);
diff --git a/drivers/gpu/drm/display/drm_dp.c b/drivers/gpu/drm/display/drm_dp_helper.c
index e7c22c2ca90c..e7c22c2ca90c 100644
--- a/drivers/gpu/drm/display/drm_dp.c
+++ b/drivers/gpu/drm/display/drm_dp_helper.c