[PATCH v4 5/5] drm/i915/dp: Disable the AUX DPCD probe quirk if it's not required

[Kahola, Mika]

> -----Original Message-----
> From: Intel-gfx <intel-gfx-bounces at lists.freedesktop.org> On Behalf Of Imre Deak
> Sent: Monday, 9 June 2025 15.56
> To: intel-gfx at lists.freedesktop.org; intel-xe at lists.freedesktop.org; dri-devel at lists.freedesktop.org
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>; Jani Nikula <jani.nikula at linux.intel.com>
> Subject: [PATCH v4 5/5] drm/i915/dp: Disable the AUX DPCD probe quirk if it's not required
> 
> Reading DPCD registers has side-effects and some of these can cause a problem for instance during link training. Based on this it's
> better to avoid the probing quirk done before each DPCD register read, limiting this to the monitor which requires it. The only
> known problematic monitor is an external SST sink, so keep the quirk disabled always for eDP and MST sinks. Reenable the quirk
> after a hotplug event and after resuming from a power state without hotplug support, until the subsequent EDID based detection.
> 
> v2: Add a helper for determining the need/setting the probing. (Jani)
> 
> Cc: Ville Syrjälä <ville.syrjala at linux.intel.com>
> Cc: Jani Nikula <jani.nikula at linux.intel.com>

Jani has already reviewed most of the patch and now that this check for dpcd probe requirement is in place, the patch looks ok to me.

Reviewed-by: Mika Kahola <mika.kahola at intel.com>

> Signed-off-by: Imre Deak <imre.deak at intel.com>
> ---
>  drivers/gpu/drm/i915/display/intel_dp.c      | 31 ++++++++++++++++++--
>  drivers/gpu/drm/i915/display/intel_dp.h      |  1 +
>  drivers/gpu/drm/i915/display/intel_dp_aux.c  |  2 ++  drivers/gpu/drm/i915/display/intel_hotplug.c |  6 ++++
>  4 files changed, 38 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index 208a953b04a2f..c089036a745fd 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -5791,6 +5791,28 @@ intel_dp_detect_sdp_caps(struct intel_dp *intel_dp)
>  		drm_dp_as_sdp_supported(&intel_dp->aux, intel_dp->dpcd);  }
> 
> +static bool intel_dp_needs_dpcd_probe(struct intel_dp *intel_dp, bool
> +force_on_external) {
> +	struct intel_connector *connector = intel_dp->attached_connector;
> +
> +	if (intel_dp_is_edp(intel_dp))
> +		return false;
> +
> +	if (force_on_external)
> +		return true;
> +
> +	if (intel_dp->is_mst)
> +		return false;
> +
> +	return drm_edid_has_quirk(&connector->base,
> +DRM_EDID_QUIRK_DP_DPCD_PROBE); }
> +
> +void intel_dp_dpcd_set_probe(struct intel_dp *intel_dp, bool
> +force_on_external) {
> +	drm_dp_dpcd_set_probe(&intel_dp->aux,
> +			      intel_dp_needs_dpcd_probe(intel_dp, force_on_external)); }
> +
>  static int
>  intel_dp_detect(struct drm_connector *_connector,
>  		struct drm_modeset_acquire_ctx *ctx,
> @@ -5919,6 +5941,8 @@ intel_dp_detect(struct drm_connector *_connector,
>  	if (status != connector_status_connected && !intel_dp->is_mst)
>  		intel_dp_unset_edid(intel_dp);
> 
> +	intel_dp_dpcd_set_probe(intel_dp, false);
> +
>  	if (!intel_dp_is_edp(intel_dp))
>  		drm_dp_set_subconnector_property(&connector->base,
>  						 status,
> @@ -5949,6 +5973,8 @@ intel_dp_force(struct drm_connector *_connector)
>  		return;
> 
>  	intel_dp_set_edid(intel_dp);
> +
> +	intel_dp_dpcd_set_probe(intel_dp, false);
>  }
> 
>  static int intel_dp_get_modes(struct drm_connector *_connector) @@ -6321,10 +6347,11 @@ intel_dp_hpd_pulse(struct
> intel_digital_port *dig_port, bool long_hpd)
>  	 * complete the DP tunnel BW request for the latter connector/encoder
>  	 * waiting for this encoder's DPRX read, perform a dummy read here.
>  	 */
> -	if (long_hpd)
> +	if (long_hpd) {
> +		intel_dp_dpcd_set_probe(intel_dp, true);
> +
>  		intel_dp_read_dprx_caps(intel_dp, dpcd);
> 
> -	if (long_hpd) {
>  		intel_dp->reset_link_params = true;
>  		intel_dp_invalidate_source_oui(intel_dp);
> 
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index eff3414c05dbf..0657f56811966 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -213,5 +213,6 @@ int intel_dp_compute_min_hblank(struct intel_crtc_state *crtc_state,
>  				const struct drm_connector_state *conn_state);
> 
>  int intel_dp_dsc_bpp_step_x16(const struct intel_connector *connector);
> +void intel_dp_dpcd_set_probe(struct intel_dp *intel_dp, bool
> +force_on_external);
> 
>  #endif /* __INTEL_DP_H__ */
> diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux.c b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> index bf8e8e0cc19c9..7bec964c0496f 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp_aux.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp_aux.c
> @@ -835,6 +835,8 @@ void intel_dp_aux_init(struct intel_dp *intel_dp)
> 
>  	intel_dp->aux.transfer = intel_dp_aux_transfer;
>  	cpu_latency_qos_add_request(&intel_dp->pm_qos, PM_QOS_DEFAULT_VALUE);
> +
> +	intel_dp_dpcd_set_probe(intel_dp, true);
>  }
> 
>  static enum aux_ch default_aux_ch(struct intel_encoder *encoder) diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c
> b/drivers/gpu/drm/i915/display/intel_hotplug.c
> index 74fe398663d63..901fda434af12 100644
> --- a/drivers/gpu/drm/i915/display/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
> @@ -33,6 +33,7 @@
>  #include "intel_display_core.h"
>  #include "intel_display_rpm.h"
>  #include "intel_display_types.h"
> +#include "intel_dp.h"
>  #include "intel_hdcp.h"
>  #include "intel_hotplug.h"
>  #include "intel_hotplug_irq.h"
> @@ -906,9 +907,14 @@ void intel_hpd_poll_enable(struct intel_display *display)
>   */
>  void intel_hpd_poll_disable(struct intel_display *display)  {
> +	struct intel_encoder *encoder;
> +
>  	if (!HAS_DISPLAY(display))
>  		return;
> 
> +	for_each_intel_dp(display->drm, encoder)
> +		intel_dp_dpcd_set_probe(enc_to_intel_dp(encoder), true);
> +
>  	WRITE_ONCE(display->hotplug.poll_enabled, false);
> 
>  	spin_lock_irq(&display->irq.lock);
> --
> 2.44.2