[PATCH] drm/amd/display: Add module param to limit max_bpc

[Harry Wentland]

Some users are reporting issues with displays not
lighting up after we made 16 bpc the default maximum
for outputs. It's difficult to debug these issues
when we can't repro them, but it'd be good to give
people the ability to help themselves.

Introduce a new amdgpu.max_bpc module param that
can be set to 8, 10, 12, 14, or 16 so users with
problematic configurations can force the output
bitdepth to a value that works for them.

Signed-off-by: Harry Wentland <harry.wentland at amd.com>
Cc: Steven J Abner <pheonix.sja at att.net>
---
 drivers/gpu/drm/amd/amdgpu/amdgpu.h               |  1 +
 drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c           | 15 +++++++++++++++
 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 11 ++++++++++-
 3 files changed, 26 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu.h b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
index 836ea081088a..35d877dabf9c 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu.h
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu.h
@@ -272,6 +272,7 @@ extern int amdgpu_rebar;
 
 extern int amdgpu_wbrf;
 extern int amdgpu_user_queue;
+extern int amdgpu_max_connector_bpc;
 
 #define AMDGPU_VM_MAX_NUM_CTX			4096
 #define AMDGPU_SG_THRESHOLD			(256*1024*1024)
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
index 4ddd08ce8885..06a889b8216f 100644
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
@@ -244,6 +244,7 @@ int amdgpu_damage_clips = -1; /* auto */
 int amdgpu_umsch_mm_fwlog;
 int amdgpu_rebar = -1; /* auto */
 int amdgpu_user_queue = -1;
+int amdgpu_max_connector_bpc = -1; /* auto */
 
 DECLARE_DYNDBG_CLASSMAP(drm_debug_classes, DD_CLASS_TYPE_DISJOINT_BITS, 0,
 			"DRM_UT_CORE",
@@ -1126,6 +1127,20 @@ module_param_named(rebar, amdgpu_rebar, int, 0444);
 MODULE_PARM_DESC(user_queue, "Enable user queues (-1 = auto (default), 0 = disable, 1 = enable, 2 = enable UQs and disable KQs)");
 module_param_named(user_queue, amdgpu_user_queue, int, 0444);
 
+/**
+ * DOC: max_bpc (int)
+ * Set the maximum connector bit-depth in bits per colors. Possible values:
+ *
+ * - -1 = auto (ASIC specific default)
+ * -  8 = 8 bpc
+ * -  10 = 10 bpc
+ * -  12 = 12 bpc
+ * -  14 = 14 bpc
+ * -  16 = 16 bpc
+ */
+MODULE_PARM_DESC(max_bpc, "Set maximum connector bpc (-1 = auto (default), 8 = 8 bpc, 10 = 10 bpc, 12 = 12 bpc, 14 = 14 bpc, 16 = 16 bpc)");
+module_param_named(max_bpc, amdgpu_max_connector_bpc, int, 0444);
+
 /* These devices are not supported by amdgpu.
  * They are supported by the mach64, r128, radeon drivers
  */
diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 4b4e9241619f..4d928984c2cd 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -8393,7 +8393,16 @@ void amdgpu_dm_connector_init_helper(struct amdgpu_display_manager *dm,
 	if (!aconnector->mst_root)
 		drm_connector_attach_max_bpc_property(&aconnector->base, 8, 16);
 
-	aconnector->base.state->max_bpc = 16;
+	if (amdgpu_max_connector_bpc != 8 &&
+	    amdgpu_max_connector_bpc != 10 &&
+	    amdgpu_max_connector_bpc != 12 &&
+	    amdgpu_max_connector_bpc != 14 &&
+	    amdgpu_max_connector_bpc != 16) {
+		drm_err(&adev->ddev, "max_bpc connector override of %d is incorrect. Needs to be 8, 10, 12, 14, or 16\n", amdgpu_max_connector_bpc);
+		amdgpu_max_connector_bpc = -1;
+	}
+
+	aconnector->base.state->max_bpc = amdgpu_max_connector_bpc == -1 ? 16 : amdgpu_max_connector_bpc;
 	aconnector->base.state->max_requested_bpc = aconnector->base.state->max_bpc;
 
 	if (connector_type == DRM_MODE_CONNECTOR_HDMIA) {
-- 
2.49.0