On Mon, May 18, 2026 at 02:24:26PM +0300, Imre Deak wrote:
> Detect DPRX capability changes without a long HPD or RX_CAP_CHANGED
> signal and queue a corresponding link params reset.
>
> Besides detecting the above unexpected capability changes, this also
> avoids races between queuing and handling a deferred link params reset.
>
> Signed-off-by: Imre Deak <[email protected]>
> ---
> drivers/gpu/drm/i915/display/intel_dp.c | 50 +++++++++++++++++++++----
> 1 file changed, 43 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c
> b/drivers/gpu/drm/i915/display/intel_dp.c
> index 6c4dadfc35806..dd968c2d9fa64 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -362,19 +362,25 @@ int intel_dp_max_source_lane_count(struct
> intel_digital_port *dig_port)
> return max_lanes;
> }
>
> -/* Theoretical max between source and sink */
> -static void intel_dp_set_max_common_lane_count(struct intel_dp *intel_dp)
> +/*
> + * Theoretical max between source and sink.
> + * Return %true if the max common lane count changed.
> + */
> +static bool intel_dp_set_max_common_lane_count(struct intel_dp *intel_dp)
> {
> struct intel_digital_port *dig_port = dp_to_dig_port(intel_dp);
> int source_max = intel_dp_max_source_lane_count(dig_port);
> int sink_max = intel_dp->max_sink_lane_count;
> int lane_max = intel_tc_port_max_lane_count(dig_port);
> int lttpr_max =
> drm_dp_lttpr_max_lane_count(intel_dp->lttpr_common_caps);
> + int old_max_common_lane_count = intel_dp->max_common_lane_count;
>
> if (lttpr_max)
> sink_max = min(sink_max, lttpr_max);
>
> intel_dp->max_common_lane_count = min3(source_max, sink_max, lane_max);
> +
> + return intel_dp->max_common_lane_count != old_max_common_lane_count;
> }
>
> int intel_dp_max_common_lane_count(struct intel_dp *intel_dp)
> @@ -792,13 +798,20 @@ int intel_dp_link_config_index(struct intel_dp
> *intel_dp, int link_rate, int lan
> return -1;
> }
>
> -static void intel_dp_set_common_rates(struct intel_dp *intel_dp)
> +/* Return %true if the common rates changed. */
> +static bool intel_dp_set_common_rates(struct intel_dp *intel_dp)
> {
> struct intel_display *display = to_intel_display(intel_dp);
> + int num_old_common_rates = intel_dp->num_common_rates;
> + int old_common_rates[DP_MAX_SUPPORTED_RATES];
>
> drm_WARN_ON(display->drm,
> !intel_dp->num_source_rates || !intel_dp->num_sink_rates);
>
> + static_assert(sizeof(old_common_rates) ==
> sizeof(intel_dp->common_rates));
Could also assert the element size/type match. Maybe (as a followup
later) introduce a proper type for this rates[]+num construct and then
we could just copy the darn thing with a normal assignment and not have
to worry about this kind of stuff at all...
> + memcpy(old_common_rates, intel_dp->common_rates,
> + num_old_common_rates * sizeof(old_common_rates[0]));
> +
> intel_dp->num_common_rates = intersect_rates(intel_dp->source_rates,
> intel_dp->num_source_rates,
> intel_dp->sink_rates,
> @@ -810,13 +823,26 @@ static void intel_dp_set_common_rates(struct intel_dp
> *intel_dp)
> intel_dp->common_rates[0] = 162000;
> intel_dp->num_common_rates = 1;
> }
> +
> + return num_old_common_rates != intel_dp->num_common_rates ||
> + memcmp(old_common_rates, intel_dp->common_rates,
> + num_old_common_rates * sizeof(old_common_rates[0]));
> }
>
> -static void intel_dp_set_common_link_params(struct intel_dp *intel_dp)
> +/* Return %true if any common link param changed. */
> +static bool intel_dp_set_common_link_params(struct intel_dp *intel_dp)
> {
> - intel_dp_set_common_rates(intel_dp);
> - intel_dp_set_max_common_lane_count(intel_dp);
> + bool params_changed = false;
> +
> + if (intel_dp_set_common_rates(intel_dp))
> + params_changed = true;
> +
> + if (intel_dp_set_max_common_lane_count(intel_dp))
> + params_changed = true;
> +
> intel_dp_link_config_init(intel_dp);
> +
> + return params_changed;
> }
>
> bool intel_dp_link_params_valid(struct intel_dp *intel_dp, int link_rate,
> @@ -4911,9 +4937,19 @@ intel_dp_has_sink_count(struct intel_dp *intel_dp)
>
> void intel_dp_update_sink_caps(struct intel_dp *intel_dp)
> {
> + struct intel_display *display = to_intel_display(intel_dp);
> +
> intel_dp_set_sink_rates(intel_dp);
> intel_dp_set_max_sink_lane_count(intel_dp);
> - intel_dp_set_common_link_params(intel_dp);
> + /*
> + * Handle unexpected sink cap changes, or a race between setting
> + * the deferred link params flag in the HPD IRQ handler and
> + * clearing the flag during connector detect.
> + */
> + if (intel_dp_set_common_link_params(intel_dp) &&
> + intel_dp_reset_link_params_defer(intel_dp))
> + drm_dbg_kms(display->drm,
> + "DPRX capabilities changed before long HPD or
> RX_CAP_CHANGED signal\n");
> }
>
> static bool
> --
> 2.49.1
--
Ville Syrjälä
Intel
