drm/vc4: hvs: Fix frame count register readout

In order to get the field currently being output, the driver has been
using the display FIFO frame count in the HVS, reading a 6-bit field at
the offset 12 in the DISPSTATx register.

While that field is indeed at that location for the FIFO 1 and 2, the
one for the FIFO0 is actually in the DISPSTAT1 register, at the offset
18.

Fixes: e538092c ("drm/vc4: Enable precise vblank timestamping for interlaced modes.")
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://lore.kernel.org/r/20220331143744.777652-3-maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_crtc.c

@@ -123,7 +123,7 @@ static bool vc4_crtc_get_scanout_position(struct drm_crtc *crtc,
 		*vpos /= 2;
 
 		/* Use hpos to correct for field offset in interlaced mode. */
-		if (VC4_GET_FIELD(val, SCALER_DISPSTATX_FRAME_COUNT) % 2)
+		if (vc4_hvs_get_fifo_frame_count(dev, vc4_crtc_state->assigned_channel) % 2)
 			*hpos += mode->crtc_htotal / 2;
 	}
 

drivers/gpu/drm/vc4/vc4_drv.h

@@ -935,6 +935,7 @@ void vc4_irq_reset(struct drm_device *dev);
 extern struct platform_driver vc4_hvs_driver;
 void vc4_hvs_stop_channel(struct drm_device *dev, unsigned int output);
 int vc4_hvs_get_fifo_from_output(struct drm_device *dev, unsigned int output);
+u8 vc4_hvs_get_fifo_frame_count(struct drm_device *dev, unsigned int fifo);
 int vc4_hvs_atomic_check(struct drm_crtc *crtc, struct drm_atomic_state *state);
 void vc4_hvs_atomic_begin(struct drm_crtc *crtc, struct drm_atomic_state *state);
 void vc4_hvs_atomic_enable(struct drm_crtc *crtc, struct drm_atomic_state *state);

drivers/gpu/drm/vc4/vc4_hvs.c

@@ -197,6 +197,29 @@ static void vc4_hvs_update_gamma_lut(struct drm_crtc *crtc)
 	vc4_hvs_lut_load(crtc);
 }
 
+u8 vc4_hvs_get_fifo_frame_count(struct drm_device *dev, unsigned int fifo)
+{
+	struct vc4_dev *vc4 = to_vc4_dev(dev);
+	u8 field = 0;
+
+	switch (fifo) {
+	case 0:
+		field = VC4_GET_FIELD(HVS_READ(SCALER_DISPSTAT1),
+				      SCALER_DISPSTAT1_FRCNT0);
+		break;
+	case 1:
+		field = VC4_GET_FIELD(HVS_READ(SCALER_DISPSTAT1),
+				      SCALER_DISPSTAT1_FRCNT1);
+		break;
+	case 2:
+		field = VC4_GET_FIELD(HVS_READ(SCALER_DISPSTAT2),
+				      SCALER_DISPSTAT2_FRCNT2);
+		break;
+	}
+
+	return field;
+}
+
 int vc4_hvs_get_fifo_from_output(struct drm_device *dev, unsigned int output)
 {
 	struct vc4_dev *vc4 = to_vc4_dev(dev);

drivers/gpu/drm/vc4/vc4_regs.h

@@ -379,8 +379,6 @@
 # define SCALER_DISPSTATX_MODE_EOF		3
 # define SCALER_DISPSTATX_FULL			BIT(29)
 # define SCALER_DISPSTATX_EMPTY			BIT(28)
-# define SCALER_DISPSTATX_FRAME_COUNT_MASK	VC4_MASK(17, 12)
-# define SCALER_DISPSTATX_FRAME_COUNT_SHIFT	12
 # define SCALER_DISPSTATX_LINE_MASK		VC4_MASK(11, 0)
 # define SCALER_DISPSTATX_LINE_SHIFT		0
 
@@ -403,9 +401,15 @@
 						 (x) * (SCALER_DISPBKGND1 - \
 							SCALER_DISPBKGND0))
 #define SCALER_DISPSTAT1                        0x00000058
+# define SCALER_DISPSTAT1_FRCNT0_MASK		VC4_MASK(23, 18)
+# define SCALER_DISPSTAT1_FRCNT0_SHIFT		18
+# define SCALER_DISPSTAT1_FRCNT1_MASK		VC4_MASK(17, 12)
+# define SCALER_DISPSTAT1_FRCNT1_SHIFT		12
+
 #define SCALER_DISPSTATX(x)			(SCALER_DISPSTAT0 +        \
 						 (x) * (SCALER_DISPSTAT1 - \
 							SCALER_DISPSTAT0))
+
 #define SCALER_DISPBASE1                        0x0000005c
 #define SCALER_DISPBASEX(x)			(SCALER_DISPBASE0 +        \
 						 (x) * (SCALER_DISPBASE1 - \
@@ -415,7 +419,11 @@
 						 (x) * (SCALER_DISPCTRL1 - \
 							SCALER_DISPCTRL0))
 #define SCALER_DISPBKGND2                       0x00000064
+
 #define SCALER_DISPSTAT2                        0x00000068
+# define SCALER_DISPSTAT2_FRCNT2_MASK		VC4_MASK(17, 12)
+# define SCALER_DISPSTAT2_FRCNT2_SHIFT		12
+
 #define SCALER_DISPBASE2                        0x0000006c
 #define SCALER_DISPALPHA2                       0x00000070
 #define SCALER_GAMADDR                          0x00000078