Message-Id: <20251018-dpu-add-dspp-gc-driver-v1-1-ed0369214252@izzo.pro>
Date: Sat, 18 Oct 2025 15:18:29 +0200
From: Federico Amedeo Izzo via B4 Relay <devnull+federico.izzo.pro@...nel.org>
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, 
 phone-devel@...r.kernel.org, ~postmarketos/upstreaming@...ts.sr.ht, 
 nicola@...na.info, Federico Amedeo Izzo <federico@...o.pro>, 
 David Heidelberg <david@...t.cz>
Subject: [PATCH] drm/msm/dpu: Add DSPP GC driver to provide GAMMA_LUT DRM
 property

From: Federico Amedeo Izzo <federico@...o.pro>

This patch adds support for DSPP GC block in DPU driver for Qualcomm SoCs.
The driver exposes the GAMMA_LUT DRM property, which is needed to enable
night light and basic screen color calibration.

I used LineageOS downstream kernel as a reference and found the LUT
format by trial-and-error on OnePlus 6.

Tested on oneplus-enchilada (sdm845-mainline 6.16-dev) and xiaomi-tissot
(msm8953-mainline 6.12/main).

Signed-off-by: Federico Amedeo Izzo <federico@...o.pro>
Tested-by: David Heidelberg <david@...t.cz>  # Pixel 3 (next-20251018)
---
DRM GAMMA_LUT support was missing on sdm845 and other Qualcomm SoCs using
DPU for CRTC. This is needed in userspace to enable features like Night
Light or basic color calibration.

I wrote this driver to enable Night Light on OnePlus 6, and after the
driver was working I found out it applies to the 29 different Qualcomm SoCs
that use the DPU display engine, including X1E for laptops.

I used the LineageOS downstream kernel as reference and found the correct 
LUT format by trial-and-error on OnePlus 6.

This was my first Linux driver and it's been a great learning
experience.

The patch was reviewed by postmarketOS contributors here: 
https://gitlab.com/sdm845-mainline/linux/-/merge_requests/137
During review the patch was tested successfully on hamoa (X1E).
---
 drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c       | 90 ++++++++++++++++++++++----
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c |  4 ++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h |  4 ++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c     |  3 +
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.c    | 56 ++++++++++++++++
 drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.h    | 26 ++++++++
 6 files changed, 169 insertions(+), 14 deletions(-)

diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
index 4b970a59deaf..f2c97c4ef0af 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_crtc.c
@@ -812,12 +812,44 @@ static void _dpu_crtc_get_pcc_coeff(struct drm_crtc_state *state,
 	cfg->b.b = CONVERT_S3_15(ctm->matrix[8]);
 }
 
+static void _dpu_crtc_get_gc_lut(struct drm_crtc_state *state,
+		struct dpu_hw_gc_lut *gc_lut)
+{
+	struct drm_color_lut *lut;
+	int i;
+	u32 val_even, val_odd;
+
+	memset(gc_lut, 0, sizeof(struct dpu_hw_gc_lut));
+
+	lut = (struct drm_color_lut *)state->gamma_lut->data;
+
+	if (!lut)
+		return;
+
+	/* Pack 1024 10-bit entries in 512 32-bit registers */
+	for (i = 0; i < PGC_TBL_LEN; i++) {
+		val_even = drm_color_lut_extract(lut[i * 2].green, 10);
+		val_odd = drm_color_lut_extract(lut[i * 2 + 1].green, 10);
+		gc_lut->c0[i] = val_even | (val_odd << 16);
+		val_even = drm_color_lut_extract(lut[i * 2].blue, 10);
+		val_odd = drm_color_lut_extract(lut[i * 2 + 1].blue, 10);
+		gc_lut->c1[i] = val_even | (val_odd << 16);
+		val_even = drm_color_lut_extract(lut[i * 2].red, 10);
+		val_odd = drm_color_lut_extract(lut[i * 2 + 1].red, 10);
+		gc_lut->c2[i] = val_even | (val_odd << 16);
+	}
+
+	/* Disable 8-bit rounding mode */
+	gc_lut->flags = 0;
+}
+
 static void _dpu_crtc_setup_cp_blocks(struct drm_crtc *crtc)
 {
 	struct drm_crtc_state *state = crtc->state;
 	struct dpu_crtc_state *cstate = to_dpu_crtc_state(crtc->state);
 	struct dpu_crtc_mixer *mixer = cstate->mixers;
 	struct dpu_hw_pcc_cfg cfg;
+	struct dpu_hw_gc_lut *gc_lut;
 	struct dpu_hw_ctl *ctl;
 	struct dpu_hw_dspp *dspp;
 	int i;
@@ -830,19 +862,40 @@ static void _dpu_crtc_setup_cp_blocks(struct drm_crtc *crtc)
 		ctl = mixer[i].lm_ctl;
 		dspp = mixer[i].hw_dspp;
 
-		if (!dspp || !dspp->ops.setup_pcc)
+		if (!dspp)
 			continue;
 
-		if (!state->ctm) {
-			dspp->ops.setup_pcc(dspp, NULL);
-		} else {
-			_dpu_crtc_get_pcc_coeff(state, &cfg);
-			dspp->ops.setup_pcc(dspp, &cfg);
+		if (dspp->ops.setup_pcc) {
+			if (!state->ctm) {
+				dspp->ops.setup_pcc(dspp, NULL);
+			} else {
+				_dpu_crtc_get_pcc_coeff(state, &cfg);
+				dspp->ops.setup_pcc(dspp, &cfg);
+			}
+
+			/* stage config flush mask */
+			ctl->ops.update_pending_flush_dspp(ctl,
+				mixer[i].hw_dspp->idx, DPU_DSPP_PCC);
 		}
 
-		/* stage config flush mask */
-		ctl->ops.update_pending_flush_dspp(ctl,
-			mixer[i].hw_dspp->idx, DPU_DSPP_PCC);
+		if (dspp->ops.setup_gc) {
+			if (!state->gamma_lut) {
+				dspp->ops.setup_gc(dspp, NULL);
+			} else {
+				gc_lut = kzalloc(sizeof(*gc_lut), GFP_KERNEL);
+				if (!gc_lut) {
+					DRM_ERROR("failed to allocate gc_lut\n");
+					continue;
+				}
+				_dpu_crtc_get_gc_lut(state, gc_lut);
+				dspp->ops.setup_gc(dspp, gc_lut);
+				kfree(gc_lut);
+			}
+
+			/* stage config flush mask */
+			ctl->ops.update_pending_flush_dspp(ctl,
+				mixer[i].hw_dspp->idx, DPU_DSPP_GC);
+		}
 	}
 }
 
@@ -1340,7 +1393,7 @@ static struct msm_display_topology dpu_crtc_get_topology(
 	 *
 	 * If DSC is enabled, use 2 LMs for 2:2:1 topology
 	 *
-	 * Add dspps to the reservation requirements if ctm is requested
+	 * Add dspps to the reservation requirements if ctm or gamma_lut are requested
 	 *
 	 * Only hardcode num_lm to 2 for cases where num_intf == 2 and CWB is not
 	 * enabled. This is because in cases where CWB is enabled, num_intf will
@@ -1359,7 +1412,7 @@ static struct msm_display_topology dpu_crtc_get_topology(
 	else
 		topology.num_lm = 1;
 
-	if (crtc_state->ctm)
+	if (crtc_state->ctm || crtc_state->gamma_lut)
 		topology.num_dspp = topology.num_lm;
 
 	return topology;
@@ -1471,7 +1524,8 @@ static int dpu_crtc_atomic_check(struct drm_crtc *crtc,
 	bool needs_dirtyfb = dpu_crtc_needs_dirtyfb(crtc_state);
 
 	/* don't reallocate resources if only ACTIVE has beeen changed */
-	if (crtc_state->mode_changed || crtc_state->connectors_changed) {
+	if (crtc_state->mode_changed || crtc_state->connectors_changed ||
+		crtc_state->color_mgmt_changed) {
 		rc = dpu_crtc_assign_resources(crtc, crtc_state);
 		if (rc < 0)
 			return rc;
@@ -1831,8 +1885,16 @@ struct drm_crtc *dpu_crtc_init(struct drm_device *dev, struct drm_plane *plane,
 
 	drm_crtc_helper_add(crtc, &dpu_crtc_helper_funcs);
 
-	if (dpu_kms->catalog->dspp_count)
-		drm_crtc_enable_color_mgmt(crtc, 0, true, 0);
+	if (dpu_kms->catalog->dspp_count) {
+		const struct dpu_dspp_cfg *dspp = &dpu_kms->catalog->dspp[0];
+
+		if (dspp->sblk->gc.base) {
+			drm_mode_crtc_set_gamma_size(crtc, DPU_GAMMA_LUT_SIZE);
+			drm_crtc_enable_color_mgmt(crtc, 0, true, DPU_GAMMA_LUT_SIZE);
+		} else {
+			drm_crtc_enable_color_mgmt(crtc, 0, true, 0);
+		}
+	}
 
 	/* save user friendly CRTC name for later */
 	snprintf(dpu_crtc->name, DPU_CRTC_NAME_SIZE, "crtc%u", crtc->base.id);
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
index 6641455c4ec6..8a4b9fc3ac84 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.c
@@ -382,11 +382,15 @@ static const struct dpu_lm_sub_blks qcm2290_lm_sblk = {
 static const struct dpu_dspp_sub_blks msm8998_dspp_sblk = {
 	.pcc = {.name = "pcc", .base = 0x1700,
 		.len = 0x90, .version = 0x10007},
+	.gc = {.name = "gc", .base = 0x17c0,
+		.len = 0x90, .version = 0x10007},
 };
 
 static const struct dpu_dspp_sub_blks sdm845_dspp_sblk = {
 	.pcc = {.name = "pcc", .base = 0x1700,
 		.len = 0x90, .version = 0x40000},
+	.gc = {.name = "gc", .base = 0x17c0,
+		.len = 0x90, .version = 0x40000},
 };
 
 static const struct dpu_dspp_sub_blks sm8750_dspp_sblk = {
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
index f0768f54e9b3..3ea67c1cf5c0 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_catalog.h
@@ -77,9 +77,11 @@ enum {
 /**
  * DSPP sub-blocks
  * @DPU_DSPP_PCC             Panel color correction block
+ * @DPU_DSPP_GC              Gamma correction block
  */
 enum {
 	DPU_DSPP_PCC = 0x1,
+	DPU_DSPP_GC,
 	DPU_DSPP_MAX
 };
 
@@ -314,9 +316,11 @@ struct dpu_lm_sub_blks {
 /**
  * struct dpu_dspp_sub_blks: Information of DSPP block
  * @pcc: pixel color correction block
+ * @gc: gamma correction block
  */
 struct dpu_dspp_sub_blks {
 	struct dpu_pp_blk pcc;
+	struct dpu_pp_blk gc;
 };
 
 struct dpu_pingpong_sub_blks {
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c
index ac834db2e4c1..36a497f1d6c1 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_ctl.c
@@ -399,6 +399,9 @@ static void dpu_hw_ctl_update_pending_flush_dspp_sub_blocks(
 	case DPU_DSPP_PCC:
 		ctx->pending_dspp_flush_mask[dspp - DSPP_0] |= BIT(4);
 		break;
+	case DPU_DSPP_GC:
+		ctx->pending_dspp_flush_mask[dspp - DSPP_0] |= BIT(5);
+		break;
 	default:
 		return;
 	}
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.c
index 54b20faa0b69..7bf572379890 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.c
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.c
@@ -24,6 +24,18 @@
 #define PCC_BLUE_G_OFF 0x24
 #define PCC_BLUE_B_OFF 0x30
 
+/* DSPP_GC */
+#define GC_EN BIT(0)
+#define GC_DIS 0
+#define GC_8B_ROUND_EN BIT(1)
+#define GC_LUT_SWAP_OFF 0x1c
+#define GC_C0_OFF 0x4
+#define GC_C1_OFF 0xC
+#define GC_C2_OFF 0x14
+#define GC_C0_INDEX_OFF 0x8
+#define GC_C1_INDEX_OFF 0x10
+#define GC_C2_INDEX_OFF 0x18
+
 static void dpu_setup_dspp_pcc(struct dpu_hw_dspp *ctx,
 		struct dpu_hw_pcc_cfg *cfg)
 {
@@ -63,6 +75,48 @@ static void dpu_setup_dspp_pcc(struct dpu_hw_dspp *ctx,
 	DPU_REG_WRITE(&ctx->hw, base, PCC_EN);
 }
 
+static void dpu_setup_dspp_gc(struct dpu_hw_dspp *ctx,
+		struct dpu_hw_gc_lut *gc_lut)
+{
+	int i = 0;
+	u32 base, reg;
+
+	if (!ctx) {
+		DRM_ERROR("invalid ctx %pK\n", ctx);
+		return;
+	}
+
+	base = ctx->cap->sblk->gc.base;
+
+	if (!base) {
+		DRM_ERROR("invalid ctx %pK gc base 0x%x\n", ctx, base);
+		return;
+	}
+
+	if (!gc_lut) {
+		DRM_DEBUG_DRIVER("disable gc feature\n");
+		DPU_REG_WRITE(&ctx->hw, base, GC_DIS);
+		return;
+	}
+
+	reg = 0;
+	DPU_REG_WRITE(&ctx->hw, base + GC_C0_INDEX_OFF, reg);
+	DPU_REG_WRITE(&ctx->hw, base + GC_C1_INDEX_OFF, reg);
+	DPU_REG_WRITE(&ctx->hw, base + GC_C2_INDEX_OFF, reg);
+
+	for (i = 0; i < PGC_TBL_LEN; i++) {
+		DPU_REG_WRITE(&ctx->hw, base + GC_C0_OFF, gc_lut->c0[i]);
+		DPU_REG_WRITE(&ctx->hw, base + GC_C1_OFF, gc_lut->c1[i]);
+		DPU_REG_WRITE(&ctx->hw, base + GC_C2_OFF, gc_lut->c2[i]);
+	}
+
+	reg = BIT(0);
+	DPU_REG_WRITE(&ctx->hw, base + GC_LUT_SWAP_OFF, reg);
+
+	reg = GC_EN | ((gc_lut->flags & PGC_8B_ROUND) ? GC_8B_ROUND_EN : 0);
+	DPU_REG_WRITE(&ctx->hw, base, reg);
+}
+
 /**
  * dpu_hw_dspp_init() - Initializes the DSPP hw driver object.
  * should be called once before accessing every DSPP.
@@ -92,6 +146,8 @@ struct dpu_hw_dspp *dpu_hw_dspp_init(struct drm_device *dev,
 	c->cap = cfg;
 	if (c->cap->sblk->pcc.base)
 		c->ops.setup_pcc = dpu_setup_dspp_pcc;
+	if (c->cap->sblk->gc.base)
+		c->ops.setup_gc = dpu_setup_dspp_gc;
 
 	return c;
 }
diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.h b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.h
index 45c26cd49fa3..d608f84e9434 100644
--- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.h
+++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_dspp.h
@@ -33,6 +33,25 @@ struct dpu_hw_pcc_cfg {
 	struct dpu_hw_pcc_coeff b;
 };
 
+#define DPU_GAMMA_LUT_SIZE 1024
+#define PGC_TBL_LEN 512
+#define PGC_8B_ROUND (1 << 0)
+
+/**
+ * struct dpu_hw_gc_lut - gc lut feature structure
+ * @flags: flags for the feature values can be:
+ *         - PGC_8B_ROUND
+ * @c0: color0 component lut
+ * @c1: color1 component lut
+ * @c2: color2 component lut
+ */
+struct dpu_hw_gc_lut {
+	__u64 flags;
+	__u32 c0[PGC_TBL_LEN];
+	__u32 c1[PGC_TBL_LEN];
+	__u32 c2[PGC_TBL_LEN];
+};
+
 /**
  * struct dpu_hw_dspp_ops - interface to the dspp hardware driver functions
  * Caller must call the init function to get the dspp context for each dspp
@@ -46,6 +65,13 @@ struct dpu_hw_dspp_ops {
 	 */
 	void (*setup_pcc)(struct dpu_hw_dspp *ctx, struct dpu_hw_pcc_cfg *cfg);
 
+	/**
+	 * setup_gc - setup dspp gc
+	 * @ctx: Pointer to dspp context
+	 * @gc_lut: Pointer to lut content
+	 */
+	void (*setup_gc)(struct dpu_hw_dspp *ctx, struct dpu_hw_gc_lut *gc_lut);
+
 };
 
 /**

---
base-commit: 2433b84761658ef123ae683508bc461b07c5b0f0
change-id: 20251017-dpu-add-dspp-gc-driver-c5d1c08be770

Best regards,
-- 
Federico Amedeo Izzo <federico@...o.pro>

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