[PATCH v2 1/2] drm/amdgpu: Add amdgpu "max bpc" connector property

[Nicholas Kazlauskas]

[Why]
Many panels support more than 8bpc but some modes are unavailable while
running at greater than 8bpc due to DP/HDMI bandwidth constraints.

Support for more than 8bpc was added recently in the driver but it
defaults to the maximum supported bpc - locking out these modes.

This should be a user configurable option such that the user can select
what bpc configuration they would like.

[How]
This patch introduces the "max bpc" amdgpu driver specific connector
property so the user can limit the maximum bpc. It ranges from 8 to 16.

This doesn't directly set the preferred bpc for the panel since it
follows Intel's existing driver conventions.

This proprety should be removed once common drm support for max bpc
lands.

Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas at amd.com>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu_display.c | 5 +++++
 drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h    | 2 ++
 2 files changed, 7 insertions(+)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
index 7d6a36bca9dd..292bfd5340fa 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_display.c
@@ -626,6 +626,11 @@ int amdgpu_display_modeset_create_props(struct amdgpu_device *adev)
 					 "dither",
 					 amdgpu_dither_enum_list, sz);
 
+	adev->mode_info.max_bpc_property =
+		drm_property_create_range(adev->ddev, 0, "max bpc", 8, 16);
+	if (!adev->mode_info.max_bpc_property)
+		return -ENOMEM;
+
 	if (amdgpu_device_has_dc_support(adev)) {
 		adev->mode_info.freesync_property =
 			drm_property_create_bool(adev->ddev, 0, "freesync");
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
index 1627dd3413c7..c39af5d79608 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_mode.h
@@ -338,6 +338,8 @@ struct amdgpu_mode_info {
 	struct drm_property *audio_property;
 	/* FMT dithering */
 	struct drm_property *dither_property;
+	/* maximum number of bits per channel for monitor color */
+	struct drm_property *max_bpc_property;
 	/* it is used to allow enablement of freesync mode */
 	struct drm_property *freesync_property;
 	/* it is used to know about display capability of freesync mode */
-- 
2.17.1