linux-kernel - [PATCH 2/2] drm/msm/dpu: try reserving the DSPP-less LM first

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Message-Id: <20260115-dpu-fix-dspp-v1-2-b73152c147b3@oss.qualcomm.com>
Date: Thu, 15 Jan 2026 22:05:39 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Rob Clark <robin.clark@....qualcomm.com>,
        Dmitry Baryshkov <lumag@...nel.org>,
        Abhinav Kumar <abhinav.kumar@...ux.dev>,
        Jessica Zhang <jesszhan0024@...il.com>, Sean Paul <sean@...rly.run>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/2] drm/msm/dpu: try reserving the DSPP-less LM first

On most of the platforms only some mixers have connected DSPP blocks.
If DSPP is not required for the CRTC, try looking for the LM with no
DSSP block, leaving DSPP-enabled LMs to CRTCs which actually require
those.

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c | 52 +++++++++++++++++++++++++---------
 1 file changed, 38 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
index 7e77d88f8959..451a4fcf3e65 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_rm.c
@@ -350,28 +350,26 @@ static bool _dpu_rm_check_lm_and_get_connected_blks(struct dpu_rm *rm,
 	return true;
 }
 
-static int _dpu_rm_reserve_lms(struct dpu_rm *rm,
-			       struct dpu_global_state *global_state,
-			       uint32_t crtc_id,
-			       struct msm_display_topology *topology)
+static bool dpu_rm_find_lms(struct dpu_rm *rm,
+			    struct dpu_global_state *global_state,
+			    uint32_t crtc_id, bool skip_dspp,
+			    struct msm_display_topology *topology,
+			    int *lm_idx, int *pp_idx, int *dspp_idx)
 
 {
-	int lm_idx[MAX_BLOCKS];
-	int pp_idx[MAX_BLOCKS];
-	int dspp_idx[MAX_BLOCKS] = {0};
 	int i, lm_count = 0;
 
-	if (!topology->num_lm) {
-		DPU_ERROR("zero LMs in topology\n");
-		return -EINVAL;
-	}
-
 	/* Find a primary mixer */
 	for (i = 0; i < ARRAY_SIZE(rm->mixer_blks) &&
 			lm_count < topology->num_lm; i++) {
 		if (!rm->mixer_blks[i])
 			continue;
 
+		if (skip_dspp && to_dpu_hw_mixer(rm->mixer_blks[i])->cap->dspp) {
+			DPU_DEBUG("Skipping LM_%d, skipping LMs with DSPPs\n", i);
+			continue;
+		}
+
 		/*
 		 * Reset lm_count to an even index. This will drop the previous
 		 * primary mixer if failed to find its peer.
@@ -410,12 +408,38 @@ static int _dpu_rm_reserve_lms(struct dpu_rm *rm,
 		}
 	}
 
-	if (lm_count != topology->num_lm) {
+	return lm_count == topology->num_lm;
+}
+
+static int _dpu_rm_reserve_lms(struct dpu_rm *rm,
+			       struct dpu_global_state *global_state,
+			       uint32_t crtc_id,
+			       struct msm_display_topology *topology)
+
+{
+	int lm_idx[MAX_BLOCKS];
+	int pp_idx[MAX_BLOCKS];
+	int dspp_idx[MAX_BLOCKS] = {0};
+	int i;
+	bool found;
+
+	if (!topology->num_lm) {
+		DPU_ERROR("zero LMs in topology\n");
+		return -EINVAL;
+	}
+
+	/* Try using non-DSPP LM blocks first */
+	found = dpu_rm_find_lms(rm, global_state, crtc_id, !topology->num_dspp,
+				topology, lm_idx, pp_idx, dspp_idx);
+	if (!found && !topology->num_dspp)
+		found = dpu_rm_find_lms(rm, global_state, crtc_id, false,
+					topology, lm_idx, pp_idx, dspp_idx);
+	if (!found) {
 		DPU_DEBUG("unable to find appropriate mixers\n");
 		return -ENAVAIL;
 	}
 
-	for (i = 0; i < lm_count; i++) {
+	for (i = 0; i < topology->num_lm; i++) {
 		global_state->mixer_to_crtc_id[lm_idx[i]] = crtc_id;
 		global_state->pingpong_to_crtc_id[pp_idx[i]] = crtc_id;
 		global_state->dspp_to_crtc_id[dspp_idx[i]] =

-- 
2.47.3