drm/stm: ltdc: add support for CRC hashing feature

This patch adds the CRC hashing feature supported by some recent hardware
versions of the LTDC. This is useful for test suite such as IGT-GPU-tools
[1] where a CRTC output frame can be compared to a test reference frame
thanks to their respective CRC hash.

[1] https://cgit.freedesktop.org/drm/igt-gpu-toolsSigned-off-by: Raphael Gallais-Pou <raphael.gallais-pou@foss.st.com>
Acked-by: Yannick Fertre <yannick.fertre@foss.st.com>
Signed-off-by: Philippe Cornu <philippe.cornu@foss.st.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220211104620.421177-1-raphael.gallais-pou@foss.st.com

drivers/gpu/drm/stm/ltdc.c

@@ -77,6 +77,7 @@
 #define LTDC_CPSR	0x0044		/* Current Position Status */
 #define LTDC_CDSR	0x0048		/* Current Display Status */
 #define LTDC_EDCR	0x0060		/* External Display Control */
+#define LTDC_CCRCR	0x007C		/* Computed CRC value */
 #define LTDC_FUT	0x0090		/* Fifo underrun Threshold */
 
 /* Layer register offsets */
@@ -121,6 +122,7 @@
 
 #define GCR_LTDCEN	BIT(0)		/* LTDC ENable */
 #define GCR_DEN		BIT(16)		/* Dither ENable */
+#define GCR_CRCEN	BIT(19)		/* CRC ENable */
 #define GCR_PCPOL	BIT(28)		/* Pixel Clock POLarity-Inverted */
 #define GCR_DEPOL	BIT(29)		/* Data Enable POLarity-High */
 #define GCR_VSPOL	BIT(30)		/* Vertical Synchro POLarity-High */
@@ -227,6 +229,13 @@
 
 #define NB_PF		8		/* Max nb of HW pixel format */
 
+/*
+ * Skip the first value and the second in case CRC was enabled during
+ * the thread irq. This is to be sure CRC value is relevant for the
+ * frame.
+ */
+#define CRC_SKIP_FRAMES 2
+
 enum ltdc_pix_fmt {
 	PF_NONE,
 	/* RGB formats */
@@ -665,6 +674,26 @@ static inline void ltdc_set_ycbcr_coeffs(struct drm_plane *plane)
 		     ltdc_ycbcr2rgb_coeffs[enc][ran][1]);
 }
 
+static inline void ltdc_irq_crc_handle(struct ltdc_device *ldev,
+				       struct drm_crtc *crtc)
+{
+	u32 crc;
+	int ret;
+
+	if (ldev->crc_skip_count < CRC_SKIP_FRAMES) {
+		ldev->crc_skip_count++;
+		return;
+	}
+
+	/* Get the CRC of the frame */
+	ret = regmap_read(ldev->regmap, LTDC_CCRCR, &crc);
+	if (ret)
+		return;
+
+	/* Report to DRM the CRC (hw dependent feature) */
+	drm_crtc_add_crc_entry(crtc, true, drm_crtc_accurate_vblank_count(crtc), &crc);
+}
+
 static irqreturn_t ltdc_irq_thread(int irq, void *arg)
 {
 	struct drm_device *ddev = arg;
@@ -672,9 +701,14 @@ static irqreturn_t ltdc_irq_thread(int irq, void *arg)
 	struct drm_crtc *crtc = drm_crtc_from_index(ddev, 0);
 
 	/* Line IRQ : trigger the vblank event */
-	if (ldev->irq_status & ISR_LIF)
+	if (ldev->irq_status & ISR_LIF) {
 		drm_crtc_handle_vblank(crtc);
 
+		/* Early return if CRC is not active */
+		if (ldev->crc_active)
+			ltdc_irq_crc_handle(ldev, crtc);
+	}
+
 	/* Save FIFO Underrun & Transfer Error status */
 	mutex_lock(&ldev->err_lock);
 	if (ldev->irq_status & ISR_FUIF)
@@ -1080,6 +1114,48 @@ static void ltdc_crtc_disable_vblank(struct drm_crtc *crtc)
 	regmap_clear_bits(ldev->regmap, LTDC_IER, IER_LIE);
 }
 
+static int ltdc_crtc_set_crc_source(struct drm_crtc *crtc, const char *source)
+{
+	struct ltdc_device *ldev = crtc_to_ltdc(crtc);
+	int ret;
+
+	DRM_DEBUG_DRIVER("\n");
+
+	if (!crtc)
+		return -ENODEV;
+
+	if (source && strcmp(source, "auto") == 0) {
+		ldev->crc_active = true;
+		ret = regmap_set_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
+	} else if (!source) {
+		ldev->crc_active = false;
+		ret = regmap_clear_bits(ldev->regmap, LTDC_GCR, GCR_CRCEN);
+	} else {
+		ret = -EINVAL;
+	}
+
+	ldev->crc_skip_count = 0;
+	return ret;
+}
+
+static int ltdc_crtc_verify_crc_source(struct drm_crtc *crtc,
+				       const char *source, size_t *values_cnt)
+{
+	DRM_DEBUG_DRIVER("\n");
+
+	if (!crtc)
+		return -ENODEV;
+
+	if (source && strcmp(source, "auto") != 0) {
+		DRM_DEBUG_DRIVER("Unknown CRC source %s for %s\n",
+				 source, crtc->name);
+		return -EINVAL;
+	}
+
+	*values_cnt = 1;
+	return 0;
+}
+
 static const struct drm_crtc_funcs ltdc_crtc_funcs = {
 	.destroy = drm_crtc_cleanup,
 	.set_config = drm_atomic_helper_set_config,
@@ -1092,6 +1168,20 @@ static const struct drm_crtc_funcs ltdc_crtc_funcs = {
 	.get_vblank_timestamp = drm_crtc_vblank_helper_get_vblank_timestamp,
 };
 
+static const struct drm_crtc_funcs ltdc_crtc_with_crc_support_funcs = {
+	.destroy = drm_crtc_cleanup,
+	.set_config = drm_atomic_helper_set_config,
+	.page_flip = drm_atomic_helper_page_flip,
+	.reset = drm_atomic_helper_crtc_reset,
+	.atomic_duplicate_state = drm_atomic_helper_crtc_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_crtc_destroy_state,
+	.enable_vblank = ltdc_crtc_enable_vblank,
+	.disable_vblank = ltdc_crtc_disable_vblank,
+	.get_vblank_timestamp = drm_crtc_vblank_helper_get_vblank_timestamp,
+	.set_crc_source = ltdc_crtc_set_crc_source,
+	.verify_crc_source = ltdc_crtc_verify_crc_source,
+};
+
 /*
  * DRM_PLANE
  */
@@ -1479,6 +1569,11 @@ static int ltdc_crtc_init(struct drm_device *ddev, struct drm_crtc *crtc)
 
 	drm_plane_create_zpos_immutable_property(primary, 0);
 
+	/* Init CRTC according to its hardware features */
+	if (ldev->caps.crc)
+		ret = drm_crtc_init_with_planes(ddev, crtc, primary, NULL,
+						&ltdc_crtc_with_crc_support_funcs, NULL);
+	else
 		ret = drm_crtc_init_with_planes(ddev, crtc, primary, NULL,
 						&ltdc_crtc_funcs, NULL);
 	if (ret) {
@@ -1630,6 +1725,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		ldev->caps.ycbcr_input = false;
 		ldev->caps.ycbcr_output = false;
 		ldev->caps.plane_reg_shadow = false;
+		ldev->caps.crc = false;
 		break;
 	case HWVER_20101:
 		ldev->caps.layer_ofs = LAY_OFS_0;
@@ -1644,6 +1740,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		ldev->caps.ycbcr_input = false;
 		ldev->caps.ycbcr_output = false;
 		ldev->caps.plane_reg_shadow = false;
+		ldev->caps.crc = false;
 		break;
 	case HWVER_40100:
 		ldev->caps.layer_ofs = LAY_OFS_1;
@@ -1658,6 +1755,7 @@ static int ltdc_get_caps(struct drm_device *ddev)
 		ldev->caps.ycbcr_input = true;
 		ldev->caps.ycbcr_output = true;
 		ldev->caps.plane_reg_shadow = true;
+		ldev->caps.crc = true;
 		break;
 	default:
 		return -ENODEV;

drivers/gpu/drm/stm/ltdc.h

@@ -27,6 +27,7 @@ struct ltdc_caps {
 	bool ycbcr_input;	/* ycbcr input converter supported */
 	bool ycbcr_output;	/* ycbcr output converter supported */
 	bool plane_reg_shadow;	/* plane shadow registers ability */
+	bool crc;		/* cyclic redundancy check supported */
 };
 
 #define LTDC_MAX_LAYER	4
@@ -46,6 +47,8 @@ struct ltdc_device {
 	u32 irq_status;
 	struct fps_info plane_fpsi[LTDC_MAX_LAYER];
 	struct drm_atomic_state *suspend_state;
+	int crc_skip_count;
+	bool crc_active;
 };
 
 int ltdc_load(struct drm_device *ddev);