Re: [PATCH 14/19] drm/i915/display: Add helper for AS SDP transmission time selection

Ville Syrjälä
2026-03-30T18:47:17Z

On Mon, Mar 30, 2026 at 09:36:51AM +0530, Ankit Nautiyal wrote:
> AS SDP may be transmitted at T1 or T2 depending on Panel Replay and
> Adaptive Sync SDP configuration as per DP 2.1. Current we are using
> T1 only, but future PR/AS SDP modes/features may require T2 or dynamic
> selection.
>
> Introduce a helper to return the appropriate AS SDP transmission time so
> that a single value is consistently used for programming PR_ALPM.
> For now this returns T1.
>
> v2: Avoid adding new member to crtc_state; use a helper. (Ville)
> v3: Clarify why AS SDP transmission time is fixed to T1. (Ville)
>
> Bspec: 68920
> Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
> ---
> drivers/gpu/drm/i915/display/intel_alpm.c | 20 +++++++++++++++++++-
> drivers/gpu/drm/i915/display/intel_dp.c | 11 +++++++++++
> drivers/gpu/drm/i915/display/intel_dp.h | 2 ++
> 3 files changed, 32 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
> index a7350ce8e716..76de24a03f61 100644
> --- a/drivers/gpu/drm/i915/display/intel_alpm.c
> +++ b/drivers/gpu/drm/i915/display/intel_alpm.c
> @@ -11,6 +11,7 @@
> #include "intel_crtc.h"
> #include "intel_de.h"
> #include "intel_display_types.h"
> +#include "intel_display_utils.h"
> #include "intel_dp.h"
> #include "intel_dp_aux.h"
> #include "intel_psr.h"
> @@ -359,6 +360,23 @@ void intel_alpm_lobf_compute_config(struct intel_dp *intel_dp,
> crtc_state->has_lobf = true;
> }
>
> +static u32 get_pr_alpm_as_sdp_transmission_time(const struct intel_crtc_state *crtc_state)
> +{
> + int as_sdp_setup_time = intel_dp_as_sdp_transmission_time();
> +
> + switch (as_sdp_setup_time) {
> + case DP_PR_AS_SDP_SETUP_TIME_T1:
> + return PR_ALPM_CTL_ADAPTIVE_SYNC_SDP_POSITION_T1;
> + case DP_PR_AS_SDP_SETUP_TIME_DYNAMIC:
> + return PR_ALPM_CTL_ADAPTIVE_SYNC_SDP_POSITION_T1_OR_T2;
> + case DP_PR_AS_SDP_SETUP_TIME_T2:
> + return PR_ALPM_CTL_ADAPTIVE_SYNC_SDP_POSITION_T2;
> + default:
> + MISSING_CASE(as_sdp_setup_time);
> + return PR_ALPM_CTL_ADAPTIVE_SYNC_SDP_POSITION_T1;
> + }
> +}
> +
> static void lnl_alpm_configure(struct intel_dp *intel_dp,
> const struct intel_crtc_state *crtc_state)
> {
> @@ -382,7 +400,7 @@ static void lnl_alpm_configure(struct intel_dp *intel_dp,
> ALPM_CTL_AUX_LESS_WAKE_TIME(crtc_state->alpm_state.aux_less_wake_lines);
>
> if (intel_dp->as_sdp_supported) {
> - u32 pr_alpm_ctl = PR_ALPM_CTL_ADAPTIVE_SYNC_SDP_POSITION_T1;
> + u32 pr_alpm_ctl = get_pr_alpm_as_sdp_transmission_time(crtc_state);
>
> if (crtc_state->link_off_after_as_sdp_when_pr_active)
> pr_alpm_ctl |= PR_ALPM_CTL_ALLOW_LINK_OFF_BETWEEN_AS_SDP_AND_SU;
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
> index b2007ffe18bc..108e97b26748 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.c
> +++ b/drivers/gpu/drm/i915/display/intel_dp.c
> @@ -7465,3 +7465,14 @@ bool intel_dp_joiner_candidate_valid(struct intel_connector *connector,
>
> return true;
> }
> +
> +int intel_dp_as_sdp_transmission_time(void)

This is a DPCD register value, so u8 would seem like the more
appropriate return type.

With that
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

> +{
> + /*
> + * DP allows AS SDP position to move during PR active in some cases, but
> + * software-controlled refresh rate changes with DC6v / ALPM require the
> + * AS SDP to remain at T1. Use T1 unconditionally for now.
> + */
> +
> + return DP_PR_AS_SDP_SETUP_TIME_T1;
> +}
> diff --git a/drivers/gpu/drm/i915/display/intel_dp.h b/drivers/gpu/drm/i915/display/intel_dp.h
> index 2849b9ecdc71..2e4609d9d05c 100644
> --- a/drivers/gpu/drm/i915/display/intel_dp.h
> +++ b/drivers/gpu/drm/i915/display/intel_dp.h
> @@ -238,4 +238,6 @@ bool intel_dp_joiner_candidate_valid(struct intel_connector *connector,
> for ((__num_joined_pipes) = 1; (__num_joined_pipes) <= (I915_MAX_PIPES); (__num_joined_pipes)++) \
> for_each_if(intel_dp_joiner_candidate_valid(__connector, (__mode)->hdisplay, __num_joined_pipes))
>
> +int intel_dp_as_sdp_transmission_time(void);
> +
> #endif /* __INTEL_DP_H__ */
> --
> 2.45.2

--
Ville Syrjälä
Intel