drm/i915/alpm: Compute LOBF late after guardband is already determined

Currently intel_alpm_lobf_compute_config() tries to account for
guardband +SCL requirements during encoder->compute_config() phase,
even before guardband is computed.
Also, LOBF depends on crtc_state->has_psr which can be modified in
encoder->compute_config_late().

Account for lobf requirements while optimizing the guardband and add
checks for final guardband in encoder->compute_config_late() phase after
the guardband and the final state of crtc_state->has_psr are already
computed.

Use crtc_state->vrr.guardband and crtc_state->set_context_latency for
the computation and add more documentation for the dependency of first
sdp position, guardband, set context latency and wake lines.

v2: Add helper to use min guardband required for lobf.
v3: Remove unrelated inadvertent changes. (Michał)
v4: Add a #FIXME note for computing wakelines based on feature. (Jouni)

Bspec:71041
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Michał Grzelak <michal.grzelak@intel.com>
Reviewed-by: Jouni Högander <jouni.hogander@intel.com>
Link: https://patch.msgid.link/20260204050250.762718-2-ankit.k.nautiyal@intel.com

4 files changed, 63 insertions, 14 deletions

diff --git a/drivers/gpu/drm/i915/display/intel_alpm.c b/drivers/gpu/drm/i915/display/intel_alpm.c
index 7ce8c674bb03..055184a3c7d5 100644
--- a/drivers/gpu/drm/i915/display/intel_alpm.c
+++ b/drivers/gpu/drm/i915/display/intel_alpm.c
@@ -15,6 +15,7 @@
 #include "intel_dp_aux.h"
 #include "intel_psr.h"
 #include "intel_psr_regs.h"
+#include "intel_vrr.h"
 
 #define SILENCE_PERIOD_MIN_TIME	80
 #define SILENCE_PERIOD_MAX_TIME	180
@@ -248,14 +249,65 @@ bool intel_alpm_compute_params(struct intel_dp *intel_dp,
 	return true;
 }
 
+int intel_alpm_lobf_min_guardband(struct intel_crtc_state *crtc_state)
+{
+	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
+	int first_sdp_position = adjusted_mode->crtc_vtotal -
+				 adjusted_mode->crtc_vsync_start;
+	int waketime_in_lines;
+
+	/*
+	 * #FIXME: Need to check if io_wake_lines or aux_less_wake_lines
+	 * is applicable. Currently this information is not readily
+	 * available in crtc_state, so max will suffice for now.
+	 */
+	waketime_in_lines = max(crtc_state->alpm_state.io_wake_lines,
+				crtc_state->alpm_state.aux_less_wake_lines);
+
+	if (!crtc_state->has_lobf)
+		return 0;
+
+	return first_sdp_position + waketime_in_lines + crtc_state->set_context_latency;
+}
+
+void intel_alpm_lobf_compute_config_late(struct intel_dp *intel_dp,
+					 struct intel_crtc_state *crtc_state)
+{
+	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
+	int waketime_in_lines, first_sdp_position;
+
+	if (!crtc_state->has_lobf)
+		return;
+
+	/*
+	 * LOBF can only be enabled if the time from the start of the SCL+Guardband
+	 * window to the position of the first SDP is greater than the time it takes
+	 * to wake the main link.
+	 *
+	 * Position of first sdp : vsync_start
+	 * start of scl + guardband : vtotal - (scl + guardband)
+	 * time in lines to wake main link : waketime_in_lines
+	 *
+	 * Position of first sdp - start of (scl + guardband) > time in lines to wake main link
+	 * vsync_start - (vtotal - (scl + guardband)) > waketime_in_lines
+	 * vsync_start - vtotal + scl + guardband > waketime_in_lines
+	 * scl + guardband > waketime_in_lines + (vtotal - vsync_start)
+	 */
+	first_sdp_position = adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vsync_start;
+	if (intel_alpm_aux_less_wake_supported(intel_dp))
+		waketime_in_lines = crtc_state->alpm_state.io_wake_lines;
+	else
+		waketime_in_lines = crtc_state->alpm_state.aux_less_wake_lines;
+
+	crtc_state->has_lobf = (crtc_state->set_context_latency + crtc_state->vrr.guardband) >
+			       (first_sdp_position + waketime_in_lines);
+}
+
 void intel_alpm_lobf_compute_config(struct intel_dp *intel_dp,
 				    struct intel_crtc_state *crtc_state,
 				    struct drm_connector_state *conn_state)
 {
 	struct intel_display *display = to_intel_display(intel_dp);
-	struct drm_display_mode *adjusted_mode = &crtc_state->hw.adjusted_mode;
-	int waketime_in_lines, first_sdp_position;
-	int context_latency, guardband;
 
 	if (intel_dp->alpm.lobf_disable_debug) {
 		drm_dbg_kms(display->drm, "LOBF is disabled by debug flag\n");
@@ -288,17 +340,7 @@ void intel_alpm_lobf_compute_config(struct intel_dp *intel_dp,
 	if (!intel_alpm_compute_params(intel_dp, crtc_state))
 		return;
 
-	context_latency = adjusted_mode->crtc_vblank_start - adjusted_mode->crtc_vdisplay;
-	guardband = adjusted_mode->crtc_vtotal -
-		    adjusted_mode->crtc_vdisplay - context_latency;
-	first_sdp_position = adjusted_mode->crtc_vtotal - adjusted_mode->crtc_vsync_start;
-	if (intel_alpm_aux_less_wake_supported(intel_dp))
-		waketime_in_lines = crtc_state->alpm_state.io_wake_lines;
-	else
-		waketime_in_lines = crtc_state->alpm_state.aux_less_wake_lines;
-
-	crtc_state->has_lobf = (context_latency + guardband) >
-		(first_sdp_position + waketime_in_lines);
+	crtc_state->has_lobf = true;
 }
 
 static void lnl_alpm_configure(struct intel_dp *intel_dp,
diff --git a/drivers/gpu/drm/i915/display/intel_alpm.h b/drivers/gpu/drm/i915/display/intel_alpm.h
index c6a4ec5b9561..b698979d1f13 100644
--- a/drivers/gpu/drm/i915/display/intel_alpm.h
+++ b/drivers/gpu/drm/i915/display/intel_alpm.h
@@ -38,4 +38,7 @@ bool intel_alpm_is_alpm_aux_less(struct intel_dp *intel_dp,
 				 const struct intel_crtc_state *crtc_state);
 void intel_alpm_disable(struct intel_dp *intel_dp);
 bool intel_alpm_get_error(struct intel_dp *intel_dp);
+void intel_alpm_lobf_compute_config_late(struct intel_dp *intel_dp,
+					 struct intel_crtc_state *crtc_state);
+int intel_alpm_lobf_min_guardband(struct intel_crtc_state *crtc_state);
 #endif
diff --git a/drivers/gpu/drm/i915/display/intel_dp.c b/drivers/gpu/drm/i915/display/intel_dp.c
index e2fd01d1a1e4..2b8f43e21174 100644
--- a/drivers/gpu/drm/i915/display/intel_dp.c
+++ b/drivers/gpu/drm/i915/display/intel_dp.c
@@ -7163,6 +7163,8 @@ int intel_dp_compute_config_late(struct intel_encoder *encoder,
 	if (ret)
 		return ret;
 
+	intel_alpm_lobf_compute_config_late(intel_dp, crtc_state);
+
 	return 0;
 }
 
diff --git a/drivers/gpu/drm/i915/display/intel_vrr.c b/drivers/gpu/drm/i915/display/intel_vrr.c
index 9d814cc2d608..00ca76dbdd6c 100644
--- a/drivers/gpu/drm/i915/display/intel_vrr.c
+++ b/drivers/gpu/drm/i915/display/intel_vrr.c
@@ -6,6 +6,7 @@
 
 #include <drm/drm_print.h>
 
+#include "intel_alpm.h"
 #include "intel_crtc.h"
 #include "intel_de.h"
 #include "intel_display_regs.h"
@@ -520,6 +521,7 @@ int intel_vrr_compute_optimized_guardband(struct intel_crtc_state *crtc_state)
 	if (intel_crtc_has_dp_encoder(crtc_state)) {
 		guardband = max(guardband, intel_psr_min_guardband(crtc_state));
 		guardband = max(guardband, intel_dp_sdp_min_guardband(crtc_state, true));
+		guardband = max(guardband, intel_alpm_lobf_min_guardband(crtc_state));
 	}
 
 	return guardband;