Re: [PATCH] drm/i915/dp: Fix link retrain loop on pre-gen8 platforms with DP adapters

[Jani Nikula <jani.nikula@linux.intel.com>]

On Thu, 30 Apr 2026, bitey <s.mavlenkov@mail.ru> wrote:
> On Ivy Bridge (and other pre-gen8 platforms), active DP-to-HDMI protocol
> converters such as the Chrontel CH73111 trigger an infinite link retrain
> loop on kernels 6.x+. The monitor connected through the adapter goes
> black and recovers approximately once per second, eventually causing
> system instability.
>
> Three changes introduced in the i915 DP stack combine to cause this:
>
> 1. intel_dp_stop_link_train() now automatically schedules a post-training
>    link check via intel_encoder_link_check_queue_work(). The Chrontel
>    adapter reports non-standard DPCD link status, which causes the check
>    to fail and trigger a retrain, looping indefinitely.
>
> 2. intel_dp_needs_link_retrain() unconditionally returns true when
>    seq_train_failures > 0, bypassing the actual DPCD link status read.
>    A single marginal training attempt permanently marks the link as
>    needing retrain.
>
> 3. intel_dp_short_pulse() forces LINK_STATUS_CHANGED on every short HPD
>    for all platforms, causing unnecessary link checks that initiate the
>    retrain cycle on adapters that generate frequent short HPDs.
>
> Fix all three by gating the new behavior behind DISPLAY_VER(display) >= 8,
> restoring the 5.15-era behavior for Ivy Bridge/Sandy Bridge and earlier.
> These platforms use the older g4x DP path and do not benefit from the
> aggressive post-training link monitoring.
>
> Tested on Intel HD 2500 (Ivy Bridge, device ID 0152) with a Chrontel
> CH73111 DP-to-HDMI adapter driving a 1920x1080 display over 2 lanes
> at HBR (270 MHz).

Please file a bug over at [1] with the full dmesg reproducing the
issues, and reply with the link to the bug.

Thanks,
Jani.


[1] https://drm.pages.freedesktop.org/intel-docs/how-to-file-i915-bugs.html


>
> Signed-off-by: bitey <s.mavlenkov@mail.ru>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c              | 8 +++++++-
>  drivers/gpu/drm/i915/display/intel_dp_link_training.c | 3 ++-
>  2 files changed, 9 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index ORIGINAL..FIXED 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5676,6 +5676,7 @@ static int
>  intel_dp_read_link_status(struct intel_dp *intel_dp,
>  			  u8 link_status[DP_LINK_STATUS_SIZE])
>  {
> +	struct intel_display *display = to_intel_display(intel_dp);
>  	int err;
>  
>  	memset(link_status, 0, DP_LINK_STATUS_SIZE);
> @@ -5712,7 +5713,8 @@ static bool intel_dp_needs_link_retrain(struct intel_dp *intel_dp)
>  	if (intel_dp->link.retrain_disabled)
>  		return false;
>  
> -	if (intel_dp->link.seq_train_failures)
> +	if (DISPLAY_VER(display) >= 8 &&
> +	    intel_dp->link.seq_train_failures)
>  		return true;
>  
>  	/* Retrain if link not ok */
> @@ -5965,6 +5967,7 @@ static bool
>  intel_dp_short_pulse(struct intel_dp *intel_dp)
>  {
> +	struct intel_display *display = to_intel_display(intel_dp);
>  	bool reprobe_needed = false;
>  	u8 esi[4] = {};
>  
> @@ -5988,7 +5991,8 @@ intel_dp_short_pulse(struct intel_dp *intel_dp)
>  	 * TODO: let the link status check depend on LINK_STATUS_CHANGED
>  	 * or intel_dp->link.force_retrain for DPCD_REV >= 1.2
>  	 */
> -	esi[3] |= LINK_STATUS_CHANGED;
> +	if (DISPLAY_VER(display) >= 8)
> +		esi[3] |= LINK_STATUS_CHANGED;
>  	if (intel_dp_handle_link_service_irq(intel_dp, esi[3]))
>  		reprobe_needed = true;
>  
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_link_training.c b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> index ORIGINAL..FIXED 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_link_training.c
> @@ -1154,7 +1154,8 @@ void intel_dp_stop_link_train(struct intel_dp *intel_dp,
>  
>  	intel_hpd_unblock(encoder);
>  
> -	if (!display->hotplug.ignore_long_hpd &&
> +	if (DISPLAY_VER(display) >= 8 &&
> +	    !display->hotplug.ignore_long_hpd &&
>  	    intel_dp->link.seq_train_failures < MAX_SEQ_TRAIN_FAILURES) {
>  		int delay_ms = intel_dp->link.seq_train_failures ? 0 : 2000;

-- 
Jani Nikula, Intel