[v3,033/105] drm/vc4: crtc: Assign output to channel automatically
diff mbox series

Message ID 5186409a2b5d290b78f6b518a2eb8e407bf1e83e.1590594512.git-series.maxime@cerno.tech
State New
Headers show
Series
  • drm/vc4: Support BCM2711 Display Pipeline
Related show

Commit Message

Maxime Ripard May 27, 2020, 3:48 p.m. UTC
The HVS found in the BCM2711 has 6 outputs and 3 FIFOs, with each output
being connected to a pixelvalve, and some muxing between the FIFOs and
outputs.

Any output cannot feed from any FIFO though, and they all have a bunch of
constraints.

In order to support this, let's store the possible FIFOs each output can be
assigned to in the vc4_crtc_data, and use that information at atomic_check
time to iterate over all the CRTCs enabled and assign them FIFOs.

The channel assigned is then set in the vc4_crtc_state so that the rest of
the driver can use it.

Signed-off-by: Maxime Ripard <maxime@cerno.tech>
---
 drivers/gpu/drm/vc4/vc4_crtc.c |  37 +++++----
 drivers/gpu/drm/vc4/vc4_drv.h  |   7 +-
 drivers/gpu/drm/vc4/vc4_kms.c  | 142 ++++++++++++++++++++++++++++++++--
 drivers/gpu/drm/vc4/vc4_regs.h |  10 ++-
 4 files changed, 172 insertions(+), 24 deletions(-)

Comments

Maxime Ripard June 16, 2020, 3:04 p.m. UTC | #1
Hi Eric,

On Wed, May 27, 2020 at 10:23:23AM -0700, Eric Anholt wrote:
> On Wed, May 27, 2020 at 8:50 AM Maxime Ripard <maxime@cerno.tech> wrote:
> >  static int
> >  vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
> >  {
> > -       int ret;
> > +       unsigned long unassigned_channels = GENMASK(NUM_CHANNELS - 1, 0);
> > +       struct drm_crtc_state *crtc_state;
> > +       struct drm_crtc *crtc;
> > +       int i, ret;
> > +
> > +       for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
> > +               struct vc4_crtc_state *vc4_crtc_state =
> > +                       to_vc4_crtc_state(crtc_state);
> > +               struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
> > +               bool is_assigned = false;
> > +               unsigned int channel;
> > +
> > +               if (!crtc_state->active)
> > +                       continue;
> > +
> > +               /*
> > +                * The problem we have to solve here is that we have
> > +                * up to 7 encoders, connected to up to 6 CRTCs.
> > +                *
> > +                * Those CRTCs, depending on the instance, can be
> > +                * routed to 1, 2 or 3 HVS FIFOs, and we need to set
> > +                * the change the muxing between FIFOs and outputs in
> > +                * the HVS accordingly.
> > +                *
> > +                * It would be pretty hard to come up with an
> > +                * algorithm that would generically solve
> > +                * this. However, the current routing trees we support
> > +                * allow us to simplify a bit the problem.
> > +                *
> > +                * Indeed, with the current supported layouts, if we
> > +                * try to assign in the ascending crtc index order the
> > +                * FIFOs, we can't fall into the situation where an
> > +                * earlier CRTC that had multiple routes is assigned
> > +                * one that was the only option for a later CRTC.
> > +                *
> > +                * If the layout changes and doesn't give us that in
> > +                * the future, we will need to have something smarter,
> > +                * but it works so far.
> > +                */
> > +               for_each_set_bit(channel, &unassigned_channels,
> > +                                sizeof(unassigned_channels)) {
> > +
> > +                       if (!(BIT(channel) & vc4_crtc->data->hvs_available_channels))
> > +                               continue;
> > +
> > +                       vc4_crtc_state->assigned_channel = channel;
> > +                       unassigned_channels &= ~BIT(channel);
> > +                       is_assigned = true;
> > +                       break;
> > +               }
> > +
> > +               if (!is_assigned)
> > +                       return -EINVAL;
> 
> I think this logic is just
> 
> int matching_channels = unassigned_channels &
> vc4_crtc->data->hvs_available_channels;
> if (matching_channels) {
>   vc4_crtc_state->assigned_channel = ffs(matching_channels) - 1;
>   unassigned_channels &= ~BIT(channel);
> } else {
>   return -EINVAL;
> }

Thanks for that suggestion (and the others), it indeed works as expected.

> If you're changing the assignment of a channel, I think you're going
> to need to set state->mode_changed or something to trigger a full
> modeset, so we don't try to just rewrite the channel of an existing
> CRTC while scanning out.

Since we won't have any CRTC configuration done outside of atomic_enable
/ atomic_disable, can we really have a case where we would reallocate a
new channel to a CRTC without that CRTC being disabled / enabled?

Maxime

Patch
diff mbox series

diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
index 580b37ad514d..a6c3f2f907bd 100644
--- a/drivers/gpu/drm/vc4/vc4_crtc.c
+++ b/drivers/gpu/drm/vc4/vc4_crtc.c
@@ -88,6 +88,7 @@  static bool vc4_crtc_get_scanout_position(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+	struct vc4_crtc_state *vc4_crtc_state = to_vc4_crtc_state(crtc->state);
 	unsigned int cob_size;
 	u32 val;
 	int fifo_lines;
@@ -104,7 +105,7 @@  static bool vc4_crtc_get_scanout_position(struct drm_crtc *crtc,
 	 * Read vertical scanline which is currently composed for our
 	 * pixelvalve by the HVS, and also the scaler status.
 	 */
-	val = HVS_READ(SCALER_DISPSTATX(vc4_crtc->channel));
+	val = HVS_READ(SCALER_DISPSTATX(vc4_crtc_state->assigned_channel));
 
 	/* Get optional system timestamp after query. */
 	if (etime)
@@ -124,7 +125,7 @@  static bool vc4_crtc_get_scanout_position(struct drm_crtc *crtc,
 			*hpos += mode->crtc_htotal / 2;
 	}
 
-	cob_size = vc4_crtc_get_cob_allocation(vc4, vc4_crtc->channel);
+	cob_size = vc4_crtc_get_cob_allocation(vc4, vc4_crtc_state->assigned_channel);
 	/* This is the offset we need for translating hvs -> pv scanout pos. */
 	fifo_lines = cob_size / mode->crtc_hdisplay;
 
@@ -211,6 +212,7 @@  vc4_crtc_lut_load(struct drm_crtc *crtc)
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+	struct vc4_crtc_state *vc4_crtc_state = to_vc4_crtc_state(crtc->state);
 	u32 i;
 
 	/* The LUT memory is laid out with each HVS channel in order,
@@ -219,7 +221,7 @@  vc4_crtc_lut_load(struct drm_crtc *crtc)
 	 */
 	HVS_WRITE(SCALER_GAMADDR,
 		  SCALER_GAMADDR_AUTOINC |
-		  (vc4_crtc->channel * 3 * crtc->gamma_size));
+		  (vc4_crtc_state->assigned_channel * 3 * crtc->gamma_size));
 
 	for (i = 0; i < crtc->gamma_size; i++)
 		HVS_WRITE(SCALER_GAMDATA, vc4_crtc->lut_r[i]);
@@ -392,7 +394,7 @@  static void vc4_crtc_mode_set_nofb(struct drm_crtc *crtc)
 		drm_print_regset32(&p, &vc4_crtc->regset);
 	}
 
-	if (vc4_crtc->channel == 2) {
+	if (vc4_crtc->data->hvs_output == 2) {
 		u32 dispctrl;
 		u32 dsp3_mux;
 
@@ -419,7 +421,7 @@  static void vc4_crtc_mode_set_nofb(struct drm_crtc *crtc)
 	if (!vc4_state->feed_txp)
 		vc4_crtc_config_pv(crtc);
 
-	HVS_WRITE(SCALER_DISPBKGNDX(vc4_crtc->channel),
+	HVS_WRITE(SCALER_DISPBKGNDX(vc4_state->assigned_channel),
 		  SCALER_DISPBKGND_AUTOHS |
 		  SCALER_DISPBKGND_GAMMA |
 		  (interlace ? SCALER_DISPBKGND_INTERLACE : 0));
@@ -451,7 +453,8 @@  static void vc4_crtc_atomic_disable(struct drm_crtc *crtc,
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
-	u32 chan = vc4_crtc->channel;
+	struct vc4_crtc_state *vc4_crtc_state = to_vc4_crtc_state(old_state);
+	u32 chan = vc4_crtc_state->assigned_channel;
 	int ret;
 	require_hvs_enabled(dev);
 
@@ -530,12 +533,12 @@  static void vc4_crtc_update_dlist(struct drm_crtc *crtc)
 			crtc->state->event = NULL;
 		}
 
-		HVS_WRITE(SCALER_DISPLISTX(vc4_crtc->channel),
+		HVS_WRITE(SCALER_DISPLISTX(vc4_state->assigned_channel),
 			  vc4_state->mm.start);
 
 		spin_unlock_irqrestore(&dev->event_lock, flags);
 	} else {
-		HVS_WRITE(SCALER_DISPLISTX(vc4_crtc->channel),
+		HVS_WRITE(SCALER_DISPLISTX(vc4_state->assigned_channel),
 			  vc4_state->mm.start);
 	}
 }
@@ -584,7 +587,7 @@  static void vc4_crtc_atomic_enable(struct drm_crtc *crtc,
 			    (vc4_state->feed_txp ?
 					SCALER5_DISPCTRLX_ONESHOT : 0);
 
-	HVS_WRITE(SCALER_DISPCTRLX(vc4_crtc->channel), dispctrl);
+	HVS_WRITE(SCALER_DISPCTRLX(vc4_state->assigned_channel), dispctrl);
 
 	/* When feeding the transposer block the pixelvalve is unneeded and
 	 * should not be enabled.
@@ -700,7 +703,6 @@  static void vc4_crtc_atomic_flush(struct drm_crtc *crtc,
 {
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
-	struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
 	struct vc4_crtc_state *vc4_state = to_vc4_crtc_state(crtc->state);
 	struct drm_plane *plane;
 	struct vc4_plane_state *vc4_plane_state;
@@ -742,8 +744,8 @@  static void vc4_crtc_atomic_flush(struct drm_crtc *crtc,
 		/* This sets a black background color fill, as is the case
 		 * with other DRM drivers.
 		 */
-		HVS_WRITE(SCALER_DISPBKGNDX(vc4_crtc->channel),
-			  HVS_READ(SCALER_DISPBKGNDX(vc4_crtc->channel)) |
+		HVS_WRITE(SCALER_DISPBKGNDX(vc4_state->assigned_channel),
+			  HVS_READ(SCALER_DISPBKGNDX(vc4_state->assigned_channel)) |
 			  SCALER_DISPBKGND_FILL);
 
 	/* Only update DISPLIST if the CRTC was already running and is not
@@ -757,7 +759,7 @@  static void vc4_crtc_atomic_flush(struct drm_crtc *crtc,
 		vc4_crtc_update_dlist(crtc);
 
 	if (crtc->state->color_mgmt_changed) {
-		u32 dispbkgndx = HVS_READ(SCALER_DISPBKGNDX(vc4_crtc->channel));
+		u32 dispbkgndx = HVS_READ(SCALER_DISPBKGNDX(vc4_state->assigned_channel));
 
 		if (crtc->state->gamma_lut) {
 			vc4_crtc_update_gamma_lut(crtc);
@@ -769,7 +771,7 @@  static void vc4_crtc_atomic_flush(struct drm_crtc *crtc,
 			 */
 			dispbkgndx &= ~SCALER_DISPBKGND_GAMMA;
 		}
-		HVS_WRITE(SCALER_DISPBKGNDX(vc4_crtc->channel), dispbkgndx);
+		HVS_WRITE(SCALER_DISPBKGNDX(vc4_state->assigned_channel), dispbkgndx);
 	}
 
 	if (debug_dump_regs) {
@@ -800,7 +802,7 @@  static void vc4_crtc_handle_page_flip(struct vc4_crtc *vc4_crtc)
 	struct drm_device *dev = crtc->dev;
 	struct vc4_dev *vc4 = to_vc4_dev(dev);
 	struct vc4_crtc_state *vc4_state = to_vc4_crtc_state(crtc->state);
-	u32 chan = vc4_crtc->channel;
+	u32 chan = vc4_state->assigned_channel;
 	unsigned long flags;
 
 	spin_lock_irqsave(&dev->event_lock, flags);
@@ -999,6 +1001,7 @@  static struct drm_crtc_state *vc4_crtc_duplicate_state(struct drm_crtc *crtc)
 	old_vc4_state = to_vc4_crtc_state(crtc->state);
 	vc4_state->feed_txp = old_vc4_state->feed_txp;
 	vc4_state->margins = old_vc4_state->margins;
+	vc4_state->assigned_channel = old_vc4_state->assigned_channel;
 
 	__drm_atomic_helper_crtc_duplicate_state(crtc, &vc4_state->base);
 	return &vc4_state->base;
@@ -1060,6 +1063,7 @@  static const struct drm_crtc_helper_funcs vc4_crtc_helper_funcs = {
 };
 
 static const struct vc4_crtc_data bcm2835_pv0_data = {
+	.hvs_available_channels = BIT(0),
 	.hvs_output = 0,
 	.debugfs_name = "crtc0_regs",
 	.pixels_per_clock = 1,
@@ -1070,6 +1074,7 @@  static const struct vc4_crtc_data bcm2835_pv0_data = {
 };
 
 static const struct vc4_crtc_data bcm2835_pv1_data = {
+	.hvs_available_channels = BIT(2),
 	.hvs_output = 2,
 	.debugfs_name = "crtc1_regs",
 	.pixels_per_clock = 1,
@@ -1080,6 +1085,7 @@  static const struct vc4_crtc_data bcm2835_pv1_data = {
 };
 
 static const struct vc4_crtc_data bcm2835_pv2_data = {
+	.hvs_available_channels = BIT(1),
 	.hvs_output = 1,
 	.debugfs_name = "crtc2_regs",
 	.pixels_per_clock = 1,
@@ -1171,7 +1177,6 @@  static int vc4_crtc_bind(struct device *dev, struct device *master, void *data)
 	drm_crtc_init_with_planes(drm, crtc, primary_plane, NULL,
 				  &vc4_crtc_funcs, NULL);
 	drm_crtc_helper_add(crtc, &vc4_crtc_helper_funcs);
-	vc4_crtc->channel = vc4_crtc->data->hvs_output;
 	drm_mode_crtc_set_gamma_size(crtc, ARRAY_SIZE(vc4_crtc->lut_r));
 	drm_crtc_enable_color_mgmt(crtc, 0, false, crtc->gamma_size);
 
diff --git a/drivers/gpu/drm/vc4/vc4_drv.h b/drivers/gpu/drm/vc4/vc4_drv.h
index 9d120aae4af9..73156a53822f 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.h
+++ b/drivers/gpu/drm/vc4/vc4_drv.h
@@ -450,6 +450,9 @@  to_vc4_encoder(struct drm_encoder *encoder)
 }
 
 struct vc4_crtc_data {
+	/* Which channels of the HVS can the output source from */
+	unsigned int hvs_available_channels;
+
 	/* Which output of the HVS this pixelvalve sources from. */
 	int hvs_output;
 
@@ -469,9 +472,6 @@  struct vc4_crtc {
 	/* Timestamp at start of vblank irq - unaffected by lock delays. */
 	ktime_t t_vblank;
 
-	/* Which HVS channel we're using for our CRTC. */
-	int channel;
-
 	u8 lut_r[256];
 	u8 lut_g[256];
 	u8 lut_b[256];
@@ -493,6 +493,7 @@  struct vc4_crtc_state {
 	struct drm_mm_node mm;
 	bool feed_txp;
 	bool txp_armed;
+	unsigned int assigned_channel;
 
 	struct {
 		unsigned int left;
diff --git a/drivers/gpu/drm/vc4/vc4_kms.c b/drivers/gpu/drm/vc4/vc4_kms.c
index 29b75b60d858..db00625c61dd 100644
--- a/drivers/gpu/drm/vc4/vc4_kms.c
+++ b/drivers/gpu/drm/vc4/vc4_kms.c
@@ -11,6 +11,8 @@ 
  * crtc, HDMI encoder).
  */
 
+#include <linux/bitfield.h>
+#include <linux/bitops.h>
 #include <linux/clk.h>
 
 #include <drm/drm_atomic.h>
@@ -146,6 +148,72 @@  vc4_ctm_commit(struct vc4_dev *vc4, struct drm_atomic_state *state)
 		  VC4_SET_FIELD(ctm_state->fifo, SCALER_OLEDOFFS_DISPFIFO));
 }
 
+static void vc4_hvs_pv_muxing_commit(struct vc4_dev *vc4,
+				     struct drm_atomic_state *state)
+{
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+	unsigned char dsp2_mux = 0;
+	unsigned char dsp3_mux = 3;
+	unsigned char dsp4_mux = 3;
+	unsigned char dsp5_mux = 3;
+	unsigned int i;
+	u32 reg;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		struct vc4_crtc_state *vc4_state = to_vc4_crtc_state(crtc_state);
+		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+
+		if (!crtc_state->active)
+			continue;
+
+		switch (vc4_crtc->data->hvs_output) {
+		case 2:
+			dsp2_mux = (vc4_state->assigned_channel == 2) ? 0 : 1;
+			break;
+
+		case 3:
+			dsp3_mux = vc4_state->assigned_channel;
+			break;
+
+		case 4:
+			dsp4_mux = vc4_state->assigned_channel;
+			break;
+
+		case 5:
+			dsp5_mux = vc4_state->assigned_channel;
+			break;
+
+		default:
+			break;
+		}
+	}
+
+	reg = HVS_READ(SCALER_DISPECTRL);
+	if (FIELD_GET(SCALER_DISPECTRL_DSP2_MUX_MASK, reg) != dsp2_mux)
+		HVS_WRITE(SCALER_DISPECTRL,
+			  (reg & ~SCALER_DISPECTRL_DSP2_MUX_MASK) |
+			  VC4_SET_FIELD(dsp2_mux, SCALER_DISPECTRL_DSP2_MUX));
+
+	reg = HVS_READ(SCALER_DISPCTRL);
+	if (FIELD_GET(SCALER_DISPCTRL_DSP3_MUX_MASK, reg) != dsp3_mux)
+		HVS_WRITE(SCALER_DISPCTRL,
+			  (reg & ~SCALER_DISPCTRL_DSP3_MUX_MASK) |
+			  VC4_SET_FIELD(dsp3_mux, SCALER_DISPCTRL_DSP3_MUX));
+
+	reg = HVS_READ(SCALER_DISPEOLN);
+	if (FIELD_GET(SCALER_DISPEOLN_DSP4_MUX_MASK, reg) != dsp4_mux)
+		HVS_WRITE(SCALER_DISPEOLN,
+			  (reg & ~SCALER_DISPEOLN_DSP4_MUX_MASK) |
+			  VC4_SET_FIELD(dsp4_mux, SCALER_DISPEOLN_DSP4_MUX));
+
+	reg = HVS_READ(SCALER_DISPDITHER);
+	if (FIELD_GET(SCALER_DISPDITHER_DSP5_MUX_MASK, reg) != dsp5_mux)
+		HVS_WRITE(SCALER_DISPDITHER,
+			  (reg & ~SCALER_DISPDITHER_DSP5_MUX_MASK) |
+			  VC4_SET_FIELD(dsp5_mux, SCALER_DISPDITHER_DSP5_MUX));
+}
+
 static void
 vc4_atomic_complete_commit(struct drm_atomic_state *state)
 {
@@ -156,11 +224,15 @@  vc4_atomic_complete_commit(struct drm_atomic_state *state)
 	int i;
 
 	for (i = 0; i < dev->mode_config.num_crtc; i++) {
-		if (!state->crtcs[i].ptr || !state->crtcs[i].commit)
+		struct __drm_crtcs_state *_state = &state->crtcs[i];
+		struct vc4_crtc_state *vc4_crtc_state;
+
+		if (!_state->ptr || !_state->commit)
 			continue;
 
-		vc4_crtc = to_vc4_crtc(state->crtcs[i].ptr);
-		vc4_hvs_mask_underrun(dev, vc4_crtc->channel);
+		vc4_crtc = to_vc4_crtc(_state->ptr);
+		vc4_crtc_state = to_vc4_crtc_state(_state->state);
+		vc4_hvs_mask_underrun(dev, vc4_crtc_state->assigned_channel);
 	}
 
 	clk_set_rate(hvs->core_clk, 500000000);
@@ -172,6 +244,7 @@  vc4_atomic_complete_commit(struct drm_atomic_state *state)
 	drm_atomic_helper_commit_modeset_disables(dev, state);
 
 	vc4_ctm_commit(vc4, state);
+	vc4_hvs_pv_muxing_commit(vc4, state);
 
 	drm_atomic_helper_commit_planes(dev, state, 0);
 
@@ -381,8 +454,11 @@  vc4_ctm_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 
 		/* CTM is being enabled or the matrix changed. */
 		if (new_crtc_state->ctm) {
+			struct vc4_crtc_state *vc4_crtc_state =
+				to_vc4_crtc_state(new_crtc_state);
+
 			/* fifo is 1-based since 0 disables CTM. */
-			int fifo = to_vc4_crtc(crtc)->channel + 1;
+			int fifo = vc4_crtc_state->assigned_channel + 1;
 
 			/* Check userland isn't trying to turn on CTM for more
 			 * than one CRTC at a time.
@@ -495,10 +571,66 @@  static const struct drm_private_state_funcs vc4_load_tracker_state_funcs = {
 	.atomic_destroy_state = vc4_load_tracker_destroy_state,
 };
 
+#define NUM_OUTPUTS  6
+#define NUM_CHANNELS 3
+
 static int
 vc4_atomic_check(struct drm_device *dev, struct drm_atomic_state *state)
 {
-	int ret;
+	unsigned long unassigned_channels = GENMASK(NUM_CHANNELS - 1, 0);
+	struct drm_crtc_state *crtc_state;
+	struct drm_crtc *crtc;
+	int i, ret;
+
+	for_each_new_crtc_in_state(state, crtc, crtc_state, i) {
+		struct vc4_crtc_state *vc4_crtc_state =
+			to_vc4_crtc_state(crtc_state);
+		struct vc4_crtc *vc4_crtc = to_vc4_crtc(crtc);
+		bool is_assigned = false;
+		unsigned int channel;
+
+		if (!crtc_state->active)
+			continue;
+
+		/*
+		 * The problem we have to solve here is that we have
+		 * up to 7 encoders, connected to up to 6 CRTCs.
+		 *
+		 * Those CRTCs, depending on the instance, can be
+		 * routed to 1, 2 or 3 HVS FIFOs, and we need to set
+		 * the change the muxing between FIFOs and outputs in
+		 * the HVS accordingly.
+		 *
+		 * It would be pretty hard to come up with an
+		 * algorithm that would generically solve
+		 * this. However, the current routing trees we support
+		 * allow us to simplify a bit the problem.
+		 *
+		 * Indeed, with the current supported layouts, if we
+		 * try to assign in the ascending crtc index order the
+		 * FIFOs, we can't fall into the situation where an
+		 * earlier CRTC that had multiple routes is assigned
+		 * one that was the only option for a later CRTC.
+		 *
+		 * If the layout changes and doesn't give us that in
+		 * the future, we will need to have something smarter,
+		 * but it works so far.
+		 */
+		for_each_set_bit(channel, &unassigned_channels,
+				 sizeof(unassigned_channels)) {
+
+			if (!(BIT(channel) & vc4_crtc->data->hvs_available_channels))
+				continue;
+
+			vc4_crtc_state->assigned_channel = channel;
+			unassigned_channels &= ~BIT(channel);
+			is_assigned = true;
+			break;
+		}
+
+		if (!is_assigned)
+			return -EINVAL;
+	}
 
 	ret = vc4_ctm_atomic_check(dev, state);
 	if (ret < 0)
diff --git a/drivers/gpu/drm/vc4/vc4_regs.h b/drivers/gpu/drm/vc4/vc4_regs.h
index 8a51baf681fe..b96ebbb1354b 100644
--- a/drivers/gpu/drm/vc4/vc4_regs.h
+++ b/drivers/gpu/drm/vc4/vc4_regs.h
@@ -287,9 +287,19 @@ 
 
 #define SCALER_DISPID                           0x00000008
 #define SCALER_DISPECTRL                        0x0000000c
+# define SCALER_DISPECTRL_DSP2_MUX_SHIFT	31
+# define SCALER_DISPECTRL_DSP2_MUX_MASK		VC4_MASK(31, 31)
+
 #define SCALER_DISPPROF                         0x00000010
+
 #define SCALER_DISPDITHER                       0x00000014
+# define SCALER_DISPDITHER_DSP5_MUX_SHIFT	30
+# define SCALER_DISPDITHER_DSP5_MUX_MASK	VC4_MASK(31, 30)
+
 #define SCALER_DISPEOLN                         0x00000018
+# define SCALER_DISPEOLN_DSP4_MUX_SHIFT		30
+# define SCALER_DISPEOLN_DSP4_MUX_MASK		VC4_MASK(31, 30)
+
 #define SCALER_DISPLIST0                        0x00000020
 #define SCALER_DISPLIST1                        0x00000024
 #define SCALER_DISPLIST2                        0x00000028