drm/amd/display: Add an hdmi_hpd_debounce_delay_ms module

[Why&How]
Right now, the HDMI HPD filter is enabled by default at 1500ms.

We want to disable it by default, as most modern displays with HDMI do
not require it for DPMS mode.

The HPD can instead be enabled as a driver parameter with a custom delay
value in ms (up to 5000ms).

Fixes: c918e75 ("drm/amd/display: Add an HPD filter for HDMI")
Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/4859
Signed-off-by: Ivan Lipski <[email protected]>
Reviewed-by: Mario Limonciello (AMD) <[email protected]>
Signed-off-by: Alex Deucher <[email protected]>
Cherry-picked-for: https://gitlab.archlinux.org/archlinux/packaging/packages/linux/-/issues/178

Author: Ivan Lipski

drivers/gpu/drm/amd/amdgpu/amdgpu.h

@@ -274,6 +274,8 @@ extern int amdgpu_rebar;
 extern int amdgpu_wbrf;
 extern int amdgpu_user_queue;
 
+extern uint amdgpu_hdmi_hpd_debounce_delay_ms;
+
 #define AMDGPU_VM_MAX_NUM_CTX			4096
 #define AMDGPU_SG_THRESHOLD			(256*1024*1024)
 #define AMDGPU_WAIT_IDLE_TIMEOUT_IN_MS	        3000

drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c

@@ -246,6 +246,7 @@ int amdgpu_damage_clips = -1; /* auto */
 int amdgpu_umsch_mm_fwlog;
 int amdgpu_rebar = -1; /* auto */
 int amdgpu_user_queue = -1;
+uint amdgpu_hdmi_hpd_debounce_delay_ms;
 
 DECLARE_DYNDBG_CLASSMAP(drm_debug_classes, DD_CLASS_TYPE_DISJOINT_BITS, 0,
 			"DRM_UT_CORE",
@@ -1128,6 +1129,16 @@ 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: hdmi_hpd_debounce_delay_ms (uint)
+ * HDMI HPD disconnect debounce delay in milliseconds.
+ *
+ * Used to filter short disconnect->reconnect HPD toggles some HDMI sinks
+ * generate while entering/leaving power save. Set to 0 to disable by default.
+ */
+MODULE_PARM_DESC(hdmi_hpd_debounce_delay_ms, "HDMI HPD disconnect debounce delay in milliseconds (0 to disable (by default), 1500 is common)");
+module_param_named(hdmi_hpd_debounce_delay_ms, amdgpu_hdmi_hpd_debounce_delay_ms, uint, 0644);
+
 /* These devices are not supported by amdgpu.
  * They are supported by the mach64, r128, radeon drivers
  */

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c

@@ -8715,9 +8715,18 @@ void amdgpu_dm_connector_init_helper(struct amdgpu_display_manager *dm,
 	mutex_init(&aconnector->hpd_lock);
 	mutex_init(&aconnector->handle_mst_msg_ready);
 
-	aconnector->hdmi_hpd_debounce_delay_ms = AMDGPU_DM_HDMI_HPD_DEBOUNCE_MS;
-	INIT_DELAYED_WORK(&aconnector->hdmi_hpd_debounce_work, hdmi_hpd_debounce_work);
-	aconnector->hdmi_prev_sink = NULL;
+	/*
+	 * If HDMI HPD debounce delay is set, use the minimum between selected
+	 * value and AMDGPU_DM_MAX_HDMI_HPD_DEBOUNCE_MS
+	 */
+	if (amdgpu_hdmi_hpd_debounce_delay_ms) {
+		aconnector->hdmi_hpd_debounce_delay_ms = min(amdgpu_hdmi_hpd_debounce_delay_ms,
+							     AMDGPU_DM_MAX_HDMI_HPD_DEBOUNCE_MS);
+		INIT_DELAYED_WORK(&aconnector->hdmi_hpd_debounce_work, hdmi_hpd_debounce_work);
+		aconnector->hdmi_prev_sink = NULL;
+	} else {
+		aconnector->hdmi_hpd_debounce_delay_ms = 0;
+	}
 
 	/*
 	 * configure support HPD hot plug connector_>polled default value is 0

drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h

@@ -59,7 +59,10 @@
 
 #define AMDGPU_HDR_MULT_DEFAULT (0x100000000LL)
 
-#define AMDGPU_DM_HDMI_HPD_DEBOUNCE_MS 1500
+/*
+ * Maximum HDMI HPD debounce delay in milliseconds
+ */
+#define AMDGPU_DM_MAX_HDMI_HPD_DEBOUNCE_MS 5000
 /*
 #include "include/amdgpu_dal_power_if.h"
 #include "amdgpu_dm_irq.h"