linux-kernel - Re: [PATCH v4 12/78] drm/vc4: crtc: Enable and disable the PV in atomic

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Date:   Tue, 28 Jul 2020 10:57:36 +0100
From:   Dave Stevenson <dave.stevenson@...pberrypi.com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Eric Anholt <eric@...olt.net>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        linux-rpi-kernel@...ts.infradead.org,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org,
        LKML <linux-kernel@...r.kernel.org>,
        Tim Gover <tim.gover@...pberrypi.com>,
        Phil Elwell <phil@...pberrypi.com>
Subject: Re: [PATCH v4 12/78] drm/vc4: crtc: Enable and disable the PV in
 atomic_enable / disable

Hi Maxime

On Wed, 8 Jul 2020 at 18:42, Maxime Ripard <maxime@...no.tech> wrote:
>
> The VIDEN bit in the pixelvalve currently being used to enable or disable
> the pixelvalve seems to not be enough in some situations, which whill end
> up with the pixelvalve stalling.
>
> In such a case, even re-enabling VIDEN doesn't bring it back and we need to
> clear the FIFO. This can only be done if the pixelvalve is disabled though.
>
> In order to overcome this, we can configure the pixelvalve during
> mode_set_no_fb, but only enable it in atomic_enable and flush the FIFO
> there, and in atomic_disable disable the pixelvalve again.

Very minor nitpick: the configure is in vc4_crtc_config_pv, but that
is called from mode_set_no_fb. The comment is correct from a DRM
overview perspective, but not from the actual code. Describing the DRM
call is probably the better approach, but it looks odd when compared
to the code.

> Signed-off-by: Maxime Ripard <maxime@...no.tech>

Reviewed-by: Dave Stevenson <dave.stevenson@...pberrypi.com>

> ---
>  drivers/gpu/drm/vc4/vc4_crtc.c | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
> index cdeaa0cd981f..fe2e5675aed4 100644
> --- a/drivers/gpu/drm/vc4/vc4_crtc.c
> +++ b/drivers/gpu/drm/vc4/vc4_crtc.c
> @@ -332,9 +332,7 @@ static void vc4_crtc_config_pv(struct drm_crtc *crtc)
>                    PV_CONTROL_TRIGGER_UNDERFLOW |
>                    PV_CONTROL_WAIT_HSTART |
>                    VC4_SET_FIELD(vc4_encoder->clock_select,
> -                                PV_CONTROL_CLK_SELECT) |
> -                  PV_CONTROL_FIFO_CLR |
> -                  PV_CONTROL_EN);
> +                                PV_CONTROL_CLK_SELECT));
>  }
>
>  static void vc4_crtc_mode_set_nofb(struct drm_crtc *crtc)
> @@ -386,6 +384,8 @@ static void vc4_crtc_atomic_disable(struct drm_crtc *crtc,
>         ret = wait_for(!(CRTC_READ(PV_V_CONTROL) & PV_VCONTROL_VIDEN), 1);
>         WARN_ONCE(ret, "Timeout waiting for !PV_VCONTROL_VIDEN\n");
>
> +       CRTC_WRITE(PV_CONTROL, CRTC_READ(PV_CONTROL) & ~PV_CONTROL_EN);
> +
>         vc4_hvs_atomic_disable(crtc, old_state);
>
>         /*
> @@ -410,6 +410,10 @@ static void vc4_crtc_atomic_enable(struct drm_crtc *crtc,
>
>         require_hvs_enabled(dev);
>
> +       /* Reset the PV fifo. */
> +       CRTC_WRITE(PV_CONTROL, CRTC_READ(PV_CONTROL) |
> +                  PV_CONTROL_FIFO_CLR | PV_CONTROL_EN);
> +
>         /* Enable vblank irq handling before crtc is started otherwise
>          * drm_crtc_get_vblank() fails in vc4_crtc_update_dlist().
>          */
> --
> git-series 0.9.1