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drm/amd/display: Add an HPD filter for HDMI

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[Why]
Some monitors perform rapid “autoscan” HPD re‑assertions right after a
disconnect or powersaving mode enablement. These appear as a quick
disconnect→reconnect with an identical EDID. Since Linux has no HDMI
hotplug detection (HPD) filter, these quick reconnects are seen as hotplug
events, which can unintentionally wake a system with DPMS off.

An example: https://gitlab.freedesktop.org/drm/amd/-/issues/2876

Such 'fake reconnects' are considered when the interval between a
disconnect and a connect is within 1500ms (experimentally chosen using
several monitors), and the two connections have the same EDID.

[How]
Implement a time-based debounce mechanism:

1. On HDMI disconnect detection, instead of immediately processing the
HPD event, save the current sink and schedule delayed work (default 1500ms)

2. If another HDMI disconnect HPD event arrives during the debounce period,
it reschedules the pending work, ensuring only the final state is processed.

3. When the debounce timer expires, re-detect the display and compare the
new sink with the cached one using EDID comparison.

4. If sinks match (same EDID), this was a spontaneous HPD toggle:
   - Update connector state internally
   - Skip hotplug event to prevent desktop rearrangement

   If sinks differ, this was a real display change:
   - Process normally with the hotplug event

The debounce delay is configurable via module parameter
'hdmi_hpd_debounce_delay_ms'.

Closes: https://gitlab.freedesktop.org/drm/amd/-/issues/2876
Reviewed-by: Sun peng (Leo) Li <sunpeng.li@amd.com>
Signed-off-by: Ivan Lipski <ivan.lipski@amd.com>
Tested-by: Dan Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
This commit is contained in:
Ivan Lipski
2025-10-30 11:25:33 -04:00
committed by Alex Deucher
parent ad1c59ad7c
commit c918e75e1e
2 changed files with 144 additions and 0 deletions
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6
drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.h
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@@ -59,6 +59,7 @@
#define AMDGPU_HDR_MULT_DEFAULT (0x100000000LL)
#define AMDGPU_DM_HDMI_HPD_DEBOUNCE_MS 1500
/*
#include "include/amdgpu_dal_power_if.h"
#include "amdgpu_dm_irq.h"
@@ -819,6 +820,11 @@ struct amdgpu_dm_connector {
bool pack_sdp_v1_3;
enum adaptive_sync_type as_type;
struct amdgpu_hdmi_vsdb_info vsdb_info;
/* HDMI HPD debounce support */
unsigned int hdmi_hpd_debounce_delay_ms;
struct delayed_work hdmi_hpd_debounce_work;
struct dc_sink *hdmi_prev_sink;
};
static inline void amdgpu_dm_set_mst_status(uint8_t *status,