[PATCH v2] drm/tidss: Fix synclost issue while disabling layer due to erratum i2097

[PATCH v2] drm/tidss: Fix synclost issue while disabling layer due to erratum i2097

[Yashas D]

A gap beyond a frame duration for disabling the layer in overlay manager
and go bit setting on the corresponding video port may lead to SYNC_LOST.
Fix by moving the layer to the non-visible area and deferring the ENABLE=0
write, immediately before the GO bit, guaranteeing both occur within the
same frame window.

Link: https://www.ti.com/lit/pdf/sprz530 # i2097

Signed-off-by: Yashas D <y-d@ti.com>
---

changelog v1->v2: 
- Flushed the pending layers in dispc_vp_disable to prevent hanging layers in hardware 
  when dispc_vp_go is not called in CRTC teardown and modeset paths.
- Removed the AM62L switch case as its the same as the default case.

Link to v1: https://lore.kernel.org/all/20260630103802.1853564-1-y-d@ti.com/

 drivers/gpu/drm/tidss/tidss_dispc.c | 118 +++++++++++++++++++++++++++-
 drivers/gpu/drm/tidss/tidss_dispc.h |   1 +
 2 files changed, 118 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
index 58d5eb033bdb..02a3cf50e0ce 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.c
+++ b/drivers/gpu/drm/tidss/tidss_dispc.c
@@ -38,6 +38,8 @@
 #include "tidss_dispc_regs.h"
 #include "tidss_scale_coefs.h"
 
+#define OVR_LAYER_MAX_POS(mask)		FIELD_MAX(mask)
+
 static const u16 tidss_k2g_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
 	[DSS_REVISION_OFF] =                    0x00,
 	[DSS_SYSCONFIG_OFF] =                   0x04,
@@ -467,6 +469,8 @@ struct dispc_device {
 
 	struct clk *fclk;
 
+	unsigned long fclk_rate;
+
 	bool is_enabled;
 
 	struct dss_vp_data vp_data[TIDSS_MAX_PORTS];
@@ -477,6 +481,9 @@ struct dispc_device {
 	u32 memory_bandwidth_limit;
 
 	struct dispc_errata errata;
+
+	/* WA for erratum i2097: OVR Layer Disable May Cause Sync Lost. */
+	u32 pending_disable_layers[TIDSS_MAX_PORTS];
 };
 
 static void dispc_write(struct dispc_device *dispc, u16 reg, u32 val)
@@ -1134,6 +1141,12 @@ void dispc_vp_prepare(struct dispc_device *dispc, u32 hw_videoport,
 	bool align, onoff, rf, ieo, ipc, ihs, ivs;
 	u32 hsw, hfp, hbp, vsw, vfp, vbp;
 
+	/*
+	 * WA for erratum i2097: clear any stale layer disable tracking
+	 * state left over from the previous VP enable/disable cycle.
+	 */
+	dispc->pending_disable_layers[hw_videoport] = 0;
+
 	fmt = dispc_vp_find_bus_fmt(dispc, hw_videoport, tstate->bus_format,
 				    tstate->bus_flags);
 
@@ -1210,6 +1223,23 @@ void dispc_vp_enable(struct dispc_device *dispc, u32 hw_videoport)
 
 void dispc_vp_disable(struct dispc_device *dispc, u32 hw_videoport)
 {
+	u32 layer;
+
+	/*
+	 * WA for erratum i2097: flush any pending layer disables directly.
+	 * dispc_vp_go() is not called in the CRTC teardown and modeset paths
+	 * so pending_disable_layers would otherwise never be consumed, leaving
+	 * layers enabled in hardware. Sync lost does not matter here since the
+	 * VP is being disabled.
+	 */
+	for (layer = 0; layer < dispc->feat->num_vids; layer++) {
+		if (dispc->pending_disable_layers[hw_videoport] & BIT(layer))
+			OVR_REG_FLD_MOD(dispc, hw_videoport,
+					DISPC_OVR_ATTRIBUTES(layer),
+					0, DISPC_OVR_ATTRIBUTES_ENABLE_MASK);
+	}
+	dispc->pending_disable_layers[hw_videoport] = 0;
+
 	VP_REG_FLD_MOD(dispc, hw_videoport, DISPC_VP_CONTROL, 0,
 		       DISPC_VP_CONTROL_ENABLE_MASK);
 }
@@ -1233,6 +1263,38 @@ void dispc_vp_go(struct dispc_device *dispc, u32 hw_videoport)
 {
 	WARN_ON(VP_REG_GET(dispc, hw_videoport, DISPC_VP_CONTROL,
 			   DISPC_VP_CONTROL_GOBIT_MASK));
+
+	if (dispc->errata.i2097 &&
+	    dispc->pending_disable_layers[hw_videoport]) {
+		u32 layer;
+		u32 delay_ns;
+
+		/* WA for erratum i2097: set GO bit #1 to latch position
+		 * changes into the DSS pipeline, wait 10 DSS functional clock
+		 * cycles, then write ENABLE=0.
+		 */
+		VP_REG_FLD_MOD(dispc, hw_videoport, DISPC_VP_CONTROL, 1,
+			       DISPC_VP_CONTROL_GOBIT_MASK);
+
+		if (dispc->fclk_rate)
+			delay_ns = DIV_ROUND_UP_ULL((u64)10 * NSEC_PER_SEC,
+						    dispc->fclk_rate);
+		else
+			delay_ns = 500;
+
+		ndelay(delay_ns);
+
+		for (layer = 0; layer < dispc->feat->num_vids; layer++) {
+			if (dispc->pending_disable_layers[hw_videoport] &
+			    BIT(layer))
+				OVR_REG_FLD_MOD(dispc, hw_videoport,
+						DISPC_OVR_ATTRIBUTES(layer),
+						0,
+						DISPC_OVR_ATTRIBUTES_ENABLE_MASK);
+		}
+		dispc->pending_disable_layers[hw_videoport] = 0;
+	}
+
 	VP_REG_FLD_MOD(dispc, hw_videoport, DISPC_VP_CONTROL, 1,
 		       DISPC_VP_CONTROL_GOBIT_MASK);
 }
@@ -1503,6 +1565,53 @@ void dispc_ovr_enable_layer(struct dispc_device *dispc,
 	if (dispc->feat->subrev == DISPC_K2G)
 		return;
 
+	if (dispc->errata.i2097 && !enable) {
+		/*
+		 * WA for erratum i2097:
+		 *
+		 * Do not write ENABLE=0 directly. Instead move the layer to
+		 * the non-visible area so it contributes no pixels.
+		 *
+		 * Position register layout differs per SoC:
+		 *   J721E : DISPC_OVR_ATTRIBUTES2, X[13:0],  Y[29:16] (14-bit)
+		 *   Others: DISPC_OVR_ATTRIBUTES,  X[17:6],  Y[30:19] (12-bit)
+		 */
+		switch (dispc->feat->subrev) {
+		case DISPC_J721E:
+			OVR_REG_FLD_MOD(dispc, hw_videoport,
+					DISPC_OVR_ATTRIBUTES2(layer),
+					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES2_POSX_MASK),
+					DISPC_OVR_ATTRIBUTES2_POSX_MASK);
+			OVR_REG_FLD_MOD(dispc, hw_videoport,
+					DISPC_OVR_ATTRIBUTES2(layer),
+					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES2_POSY_MASK),
+					DISPC_OVR_ATTRIBUTES2_POSY_MASK);
+			break;
+		default:
+			OVR_REG_FLD_MOD(dispc, hw_videoport,
+					DISPC_OVR_ATTRIBUTES(layer),
+					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES_POSX_MASK),
+					DISPC_OVR_ATTRIBUTES_POSX_MASK);
+			OVR_REG_FLD_MOD(dispc, hw_videoport,
+					DISPC_OVR_ATTRIBUTES(layer),
+					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES_POSY_MASK),
+					DISPC_OVR_ATTRIBUTES_POSY_MASK);
+			break;
+		}
+
+		dispc->pending_disable_layers[hw_videoport] |= BIT(layer);
+		return;
+	}
+
+	if (dispc->errata.i2097 && enable) {
+		/*
+		 * Layer being re-enabled: cancel any pending disable so
+		 * dispc_vp_go() does not write ENABLE=0 after we have
+		 * just written ENABLE=1 here.
+		 */
+		dispc->pending_disable_layers[hw_videoport] &= ~BIT(layer);
+	}
+
 	OVR_REG_FLD_MOD(dispc, hw_videoport, DISPC_OVR_ATTRIBUTES(layer),
 			!!enable, DISPC_OVR_ATTRIBUTES_ENABLE_MASK);
 }
@@ -2871,6 +2980,12 @@ static void dispc_init_errata(struct dispc_device *dispc)
 		dispc->errata.i2000 = true;
 		dev_info(dispc->dev, "WA for erratum i2000: YUV formats disabled\n");
 	}
+
+	if (dispc->feat->subrev != DISPC_K2G) {
+		dispc->errata.i2097 = true;
+		dev_info(dispc->dev,
+			 "WA for erratum i2097: OVR layer disable uses non-visible area\n");
+	}
 }
 
 /*
@@ -3059,7 +3174,8 @@ int dispc_init(struct tidss_device *tidss)
 			__func__, PTR_ERR(dispc->fclk));
 		return PTR_ERR(dispc->fclk);
 	}
-	dev_dbg(dev, "DSS fclk %lu Hz\n", clk_get_rate(dispc->fclk));
+	dispc->fclk_rate = clk_get_rate(dispc->fclk);
+	dev_dbg(dev, "DSS fclk %lu Hz\n", dispc->fclk_rate);
 
 	of_property_read_u32(dispc->dev->of_node, "max-memory-bandwidth",
 			     &dispc->memory_bandwidth_limit);
diff --git a/drivers/gpu/drm/tidss/tidss_dispc.h b/drivers/gpu/drm/tidss/tidss_dispc.h
index 739d211d0018..e2ce9fdf1279 100644
--- a/drivers/gpu/drm/tidss/tidss_dispc.h
+++ b/drivers/gpu/drm/tidss/tidss_dispc.h
@@ -57,6 +57,7 @@ struct dispc_vid_info {
 
 struct dispc_errata {
 	bool i2000; /* DSS Does Not Support YUV Pixel Data Formats */
+	bool i2097; /* OVR Layer Disable May Cause Sync Lost */
 };
 
 enum dispc_vp_bus_type {
-- 
2.34.1

Re: [PATCH v2] drm/tidss: Fix synclost issue while disabling layer due to erratum i2097

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] The workaround for erratum i2097 incorrectly moves disabled layers to (-1, -1) on-screen instead of a non-visible off-screen area, causing a visual glitch.
--

commit 80e2da1fc464e6c124d0362e7f424161a94f05ab
Author: Yashas D <y-d@ti.com>

drm/tidss: Fix synclost issue while disabling layer due to erratum i2097

A gap beyond a frame duration for disabling the layer in overlay manager
and go bit setting on the corresponding video port may lead to SYNC_LOST.
Fix by moving the layer to the non-visible area and deferring the ENABLE=0
write, immediately before the GO bit, guaranteeing both occur within the
same frame window.

Link: https://www.ti.com/lit/pdf/sprz530 # i2097

> diff --git a/drivers/gpu/drm/tidss/tidss_dispc.c b/drivers/gpu/drm/tidss/tidss_dispc.c
> index 58d5eb033bdbb..02a3cf50e0ceb 100644
> --- a/drivers/gpu/drm/tidss/tidss_dispc.c
> +++ b/drivers/gpu/drm/tidss/tidss_dispc.c
> @@ -38,6 +38,8 @@
>  #include "tidss_dispc_regs.h"
>  #include "tidss_scale_coefs.h"
>  
> +#define OVR_LAYER_MAX_POS(mask)		FIELD_MAX(mask)
> +
>  static const u16 tidss_k2g_common_regs[DISPC_COMMON_REG_TABLE_LEN] = {
>  	[DSS_REVISION_OFF] =                    0x00,

[ ... ]

> @@ -1503,6 +1565,53 @@ void dispc_ovr_enable_layer(struct dispc_device *dispc,
>  	if (dispc->feat->subrev == DISPC_K2G)
>  		return;
>  
> +	if (dispc->errata.i2097 && !enable) {
> +		/*
> +		 * WA for erratum i2097:
> +		 *
> +		 * Do not write ENABLE=0 directly. Instead move the layer to
> +		 * the non-visible area so it contributes no pixels.
> +		 *
> +		 * Position register layout differs per SoC:
> +		 *   J721E : DISPC_OVR_ATTRIBUTES2, X[13:0],  Y[29:16] (14-bit)
> +		 *   Others: DISPC_OVR_ATTRIBUTES,  X[17:6],  Y[30:19] (12-bit)
> +		 */
> +		switch (dispc->feat->subrev) {
> +		case DISPC_J721E:
> +			OVR_REG_FLD_MOD(dispc, hw_videoport,
> +					DISPC_OVR_ATTRIBUTES2(layer),
> +					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES2_POSX_MASK),
> +					DISPC_OVR_ATTRIBUTES2_POSX_MASK);
> +			OVR_REG_FLD_MOD(dispc, hw_videoport,
> +					DISPC_OVR_ATTRIBUTES2(layer),
> +					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES2_POSY_MASK),
> +					DISPC_OVR_ATTRIBUTES2_POSY_MASK);
> +			break;
> +		default:
> +			OVR_REG_FLD_MOD(dispc, hw_videoport,
> +					DISPC_OVR_ATTRIBUTES(layer),
> +					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES_POSX_MASK),
> +					DISPC_OVR_ATTRIBUTES_POSX_MASK);

[Severity: Medium]
Will this move the disabled layer to position (-1, -1) rather than a
non-visible off-screen area?

If the hardware interprets the POSX and POSY register bitfields as signed
integers (two's complement), setting the coordinates using OVR_LAYER_MAX_POS
which evaluates to FIELD_MAX(mask) (an all-ones bit pattern) will result
in -1.

This could cause a visual glitch where the disabled layer flashes at the
top-left corner of the screen instead of being hidden.

Does OVR_LAYER_MAX_POS in dispc_ovr_enable_layer() need to avoid setting the
sign bit to properly move the layer off-screen during normal KMS operations?

> +			OVR_REG_FLD_MOD(dispc, hw_videoport,
> +					DISPC_OVR_ATTRIBUTES(layer),
> +					OVR_LAYER_MAX_POS(DISPC_OVR_ATTRIBUTES_POSY_MASK),
> +					DISPC_OVR_ATTRIBUTES_POSY_MASK);
> +			break;
> +		}
> +
> +		dispc->pending_disable_layers[hw_videoport] |= BIT(layer);
> +		return;
> +	}

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260701063337.2165966-1-y-d@ti.com?part=1