[PATCH 0/2] drm: rcar-du: Avoid flicker when enabling a VSP plane

[PATCH 0/2] drm: rcar-du: Avoid flicker when enabling a VSP plane

[Laurent Pinchart]

Hello,

This patch series avoids flicker in some scenarios related to dual
output configuration.

The issue was originally reported by Michael Rodin in [1]. The problem
is described in details there, and copied here to facilitate discussion:

--------
Restarting a display unit group can cause a visible flicker on the display.
Particularly when a LVDS display is connected to a Salvator board and an
HDMI display is (re)connected, then there will be 2 visible flickers on the
LVDS display:

 1. during atomic_flush (The need_restart flag is set in this case by
    rcar_du_vsp_enable.):
  rcar_du_crtc_atomic_flush
    rcar_du_crtc_update_planes
      ...
      ...
      /* Restart the group if plane sources have changed. */
      if (rcrtc->group->need_restart)
              rcar_du_group_restart(rcrtc->group);
 2. during atomic_enable:
  rcar_du_crtc_atomic_enable
    rcar_du_crtc_start
      rcar_du_group_start_stop(rcrtc->group, true);

To avoid flickers in all use cases, do not restart DU groups on the Gen3
SoCs at all, since it is not required any more.
--------

The proposed patch unfortunately introduced a regression. This series
fixes the issue in the first scenario described above. The second
scenario still leads to flicker, and I don't think that can be fixed as
the hardware requires the whole group of outputs to be stopped for some
register changes to take effect.

[1] https://lore.kernel.org/dri-devel/1637680811-90510-1-git-send-email-mrodin@de.adit-jv.com

Laurent Pinchart (2):
  drm: rcar-du: Don't select VSP1 sink on Gen3
  drm: rcar-du: Don't restart group when enabling plane on Gen3

 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 12 ++++++++++--
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c   |  9 ---------
 2 files changed, 10 insertions(+), 11 deletions(-)

-- 
Regards,

Laurent Pinchart

[PATCH 0/2] drm: rcar-du: Avoid flicker when enabling a VSP plane

[Laurent Pinchart]

Hello,

This patch series avoids flicker in some scenarios related to dual
output configuration.

The issue was originally reported by Michael Rodin in [1]. The problem
is described in details there, and copied here to facilitate discussion:

--------
Restarting a display unit group can cause a visible flicker on the display.
Particularly when a LVDS display is connected to a Salvator board and an
HDMI display is (re)connected, then there will be 2 visible flickers on the
LVDS display:

 1. during atomic_flush (The need_restart flag is set in this case by
    rcar_du_vsp_enable.):
  rcar_du_crtc_atomic_flush
    rcar_du_crtc_update_planes
      ...
      ...
      /* Restart the group if plane sources have changed. */
      if (rcrtc->group->need_restart)
              rcar_du_group_restart(rcrtc->group);
 2. during atomic_enable:
  rcar_du_crtc_atomic_enable
    rcar_du_crtc_start
      rcar_du_group_start_stop(rcrtc->group, true);

To avoid flickers in all use cases, do not restart DU groups on the Gen3
SoCs at all, since it is not required any more.
--------

The proposed patch unfortunately introduced a regression. This series
fixes the issue in the first scenario described above. The second
scenario still leads to flicker, and I don't think that can be fixed as
the hardware requires the whole group of outputs to be stopped for some
register changes to take effect.

[1] https://lore.kernel.org/dri-devel/1637680811-90510-1-git-send-email-mrodin@de.adit-jv.com

Laurent Pinchart (2):
  drm: rcar-du: Don't select VSP1 sink on Gen3
  drm: rcar-du: Don't restart group when enabling plane on Gen3

 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 12 ++++++++++--
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c   |  9 ---------
 2 files changed, 10 insertions(+), 11 deletions(-)

-- 
Regards,

Laurent Pinchart

[PATCH 1/2] drm: rcar-du: Don't select VSP1 sink on Gen3

[Laurent Pinchart]

The VSP1 sink selection through register DEFR8 is only available on Gen2
hardware. Skip it on Gen3.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 862197be1e01..9b058d6cb032 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -549,8 +549,10 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
 		rcar_du_plane_setup_format(rgrp, (state->hwindex + 1) % 8,
 					   state);
 
-	if (rcdu->info->gen < 3)
-		rcar_du_plane_setup_scanout(rgrp, state);
+	if (rcdu->info->gen >= 3)
+		return;
+
+	rcar_du_plane_setup_scanout(rgrp, state);
 
 	if (state->source == RCAR_DU_PLANE_VSPD1) {
 		unsigned int vspd1_sink = rgrp->index ? 2 : 0;
-- 
Regards,

Laurent Pinchart

[PATCH 1/2] drm: rcar-du: Don't select VSP1 sink on Gen3

[Laurent Pinchart]

The VSP1 sink selection through register DEFR8 is only available on Gen2
hardware. Skip it on Gen3.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 862197be1e01..9b058d6cb032 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -549,8 +549,10 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
 		rcar_du_plane_setup_format(rgrp, (state->hwindex + 1) % 8,
 					   state);
 
-	if (rcdu->info->gen < 3)
-		rcar_du_plane_setup_scanout(rgrp, state);
+	if (rcdu->info->gen >= 3)
+		return;
+
+	rcar_du_plane_setup_scanout(rgrp, state);
 
 	if (state->source == RCAR_DU_PLANE_VSPD1) {
 		unsigned int vspd1_sink = rgrp->index ? 2 : 0;
-- 
Regards,

Laurent Pinchart

[PATCH 2/2] drm: rcar-du: Don't restart group when enabling plane on Gen3

[Laurent Pinchart]

On Gen3 hardware enabling a VSP plane doesn't change any register that
requires DRES to take effect. Avoid a group restart in that case.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++++
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 9 ---------
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 9b058d6cb032..22aeeb1cc1fb 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -560,6 +560,12 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
 		if (rcdu->vspd1_sink != vspd1_sink) {
 			rcdu->vspd1_sink = vspd1_sink;
 			rcar_du_set_dpad0_vsp1_routing(rcdu);
+
+			/*
+			 * Changes to the VSP1 sink take effect on DRES and thus
+			 * need a restart of the group.
+			 */
+			rgrp->need_restart = true;
 		}
 	}
 }
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index b7fc5b069cbc..32530d698e75 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -84,15 +84,6 @@ void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
 
 	__rcar_du_plane_setup(crtc->group, &state);
 
-	/*
-	 * Ensure that the plane source configuration takes effect by requesting
-	 * a restart of the group. See rcar_du_plane_atomic_update() for a more
-	 * detailed explanation.
-	 *
-	 * TODO: Check whether this is still needed on Gen3.
-	 */
-	crtc->group->need_restart = true;
-
 	vsp1_du_setup_lif(crtc->vsp->vsp, crtc->vsp_pipe, &cfg);
 }
 
-- 
Regards,

Laurent Pinchart

[PATCH 2/2] drm: rcar-du: Don't restart group when enabling plane on Gen3

[Laurent Pinchart]

On Gen3 hardware enabling a VSP plane doesn't change any register that
requires DRES to take effect. Avoid a group restart in that case.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
---
 drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++++
 drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 9 ---------
 2 files changed, 6 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
index 9b058d6cb032..22aeeb1cc1fb 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
@@ -560,6 +560,12 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
 		if (rcdu->vspd1_sink != vspd1_sink) {
 			rcdu->vspd1_sink = vspd1_sink;
 			rcar_du_set_dpad0_vsp1_routing(rcdu);
+
+			/*
+			 * Changes to the VSP1 sink take effect on DRES and thus
+			 * need a restart of the group.
+			 */
+			rgrp->need_restart = true;
 		}
 	}
 }
diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
index b7fc5b069cbc..32530d698e75 100644
--- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
+++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
@@ -84,15 +84,6 @@ void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
 
 	__rcar_du_plane_setup(crtc->group, &state);
 
-	/*
-	 * Ensure that the plane source configuration takes effect by requesting
-	 * a restart of the group. See rcar_du_plane_atomic_update() for a more
-	 * detailed explanation.
-	 *
-	 * TODO: Check whether this is still needed on Gen3.
-	 */
-	crtc->group->need_restart = true;
-
 	vsp1_du_setup_lif(crtc->vsp->vsp, crtc->vsp_pipe, &cfg);
 }
 
-- 
Regards,

Laurent Pinchart

Re: [PATCH 1/2] drm: rcar-du: Don't select VSP1 sink on Gen3

[Kieran Bingham]

Quoting Laurent Pinchart (2022-02-21 17:13:39)
> The VSP1 sink selection through register DEFR8 is only available on Gen2
> hardware. Skip it on Gen3.

aha, interesting, and I see how this leads into the second patch.

Looks fine on it's own too though:

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> index 862197be1e01..9b058d6cb032 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -549,8 +549,10 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
>                 rcar_du_plane_setup_format(rgrp, (state->hwindex + 1) % 8,
>                                            state);
>  
> -       if (rcdu->info->gen < 3)
> -               rcar_du_plane_setup_scanout(rgrp, state);
> +       if (rcdu->info->gen >= 3)
> +               return;
> +
> +       rcar_du_plane_setup_scanout(rgrp, state);
>  
>         if (state->source == RCAR_DU_PLANE_VSPD1) {
>                 unsigned int vspd1_sink = rgrp->index ? 2 : 0;
> -- 
> Regards,
> 
> Laurent Pinchart
>

Re: [PATCH 1/2] drm: rcar-du: Don't select VSP1 sink on Gen3

[Kieran Bingham]

Quoting Laurent Pinchart (2022-02-21 17:13:39)
> The VSP1 sink selection through register DEFR8 is only available on Gen2
> hardware. Skip it on Gen3.

aha, interesting, and I see how this leads into the second patch.

Looks fine on it's own too though:

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> index 862197be1e01..9b058d6cb032 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -549,8 +549,10 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
>                 rcar_du_plane_setup_format(rgrp, (state->hwindex + 1) % 8,
>                                            state);
>  
> -       if (rcdu->info->gen < 3)
> -               rcar_du_plane_setup_scanout(rgrp, state);
> +       if (rcdu->info->gen >= 3)
> +               return;
> +
> +       rcar_du_plane_setup_scanout(rgrp, state);
>  
>         if (state->source == RCAR_DU_PLANE_VSPD1) {
>                 unsigned int vspd1_sink = rgrp->index ? 2 : 0;
> -- 
> Regards,
> 
> Laurent Pinchart
>

Re: [PATCH 2/2] drm: rcar-du: Don't restart group when enabling plane on Gen3

[Kieran Bingham]

Quoting Laurent Pinchart (2022-02-21 17:13:40)
> On Gen3 hardware enabling a VSP plane doesn't change any register that
> requires DRES to take effect. Avoid a group restart in that case.

This also makes it clear that the need_restart is due to the change
occuring in the VSP1 sink, so I think this is cleaner all round.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++++
>  drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 9 ---------
>  2 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> index 9b058d6cb032..22aeeb1cc1fb 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -560,6 +560,12 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
>                 if (rcdu->vspd1_sink != vspd1_sink) {
>                         rcdu->vspd1_sink = vspd1_sink;
>                         rcar_du_set_dpad0_vsp1_routing(rcdu);
> +
> +                       /*
> +                        * Changes to the VSP1 sink take effect on DRES and thus
> +                        * need a restart of the group.
> +                        */
> +                       rgrp->need_restart = true;
>                 }
>         }
>  }
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> index b7fc5b069cbc..32530d698e75 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> @@ -84,15 +84,6 @@ void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
>  
>         __rcar_du_plane_setup(crtc->group, &state);
>  
> -       /*
> -        * Ensure that the plane source configuration takes effect by requesting
> -        * a restart of the group. See rcar_du_plane_atomic_update() for a more
> -        * detailed explanation.
> -        *
> -        * TODO: Check whether this is still needed on Gen3.
> -        */
> -       crtc->group->need_restart = true;
> -
>         vsp1_du_setup_lif(crtc->vsp->vsp, crtc->vsp_pipe, &cfg);
>  }
>  
> -- 
> Regards,
> 
> Laurent Pinchart
>

Re: [PATCH 2/2] drm: rcar-du: Don't restart group when enabling plane on Gen3

[Kieran Bingham]

Quoting Laurent Pinchart (2022-02-21 17:13:40)
> On Gen3 hardware enabling a VSP plane doesn't change any register that
> requires DRES to take effect. Avoid a group restart in that case.

This also makes it clear that the need_restart is due to the change
occuring in the VSP1 sink, so I think this is cleaner all round.

Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>

> 
> Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
> ---
>  drivers/gpu/drm/rcar-du/rcar_du_plane.c | 6 ++++++
>  drivers/gpu/drm/rcar-du/rcar_du_vsp.c   | 9 ---------
>  2 files changed, 6 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_plane.c b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> index 9b058d6cb032..22aeeb1cc1fb 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_plane.c
> @@ -560,6 +560,12 @@ void __rcar_du_plane_setup(struct rcar_du_group *rgrp,
>                 if (rcdu->vspd1_sink != vspd1_sink) {
>                         rcdu->vspd1_sink = vspd1_sink;
>                         rcar_du_set_dpad0_vsp1_routing(rcdu);
> +
> +                       /*
> +                        * Changes to the VSP1 sink take effect on DRES and thus
> +                        * need a restart of the group.
> +                        */
> +                       rgrp->need_restart = true;
>                 }
>         }
>  }
> diff --git a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> index b7fc5b069cbc..32530d698e75 100644
> --- a/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> +++ b/drivers/gpu/drm/rcar-du/rcar_du_vsp.c
> @@ -84,15 +84,6 @@ void rcar_du_vsp_enable(struct rcar_du_crtc *crtc)
>  
>         __rcar_du_plane_setup(crtc->group, &state);
>  
> -       /*
> -        * Ensure that the plane source configuration takes effect by requesting
> -        * a restart of the group. See rcar_du_plane_atomic_update() for a more
> -        * detailed explanation.
> -        *
> -        * TODO: Check whether this is still needed on Gen3.
> -        */
> -       crtc->group->need_restart = true;
> -
>         vsp1_du_setup_lif(crtc->vsp->vsp, crtc->vsp_pipe, &cfg);
>  }
>  
> -- 
> Regards,
> 
> Laurent Pinchart
>