linux-kernel - Re: [PATCH v4 70/78] drm/vc4: hdmi: Always recenter the HDMI FIFO

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Date:   Tue, 28 Jul 2020 16:03:04 +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 70/78] drm/vc4: hdmi: Always recenter the HDMI FIFO

Hi Maxime

On Wed, 8 Jul 2020 at 18:44, Maxime Ripard <maxime@...no.tech> wrote:
>
> In order to avoid a pixel getting stuck in an unflushable FIFO, we need to
> recenter the FIFO every time we're doing a modeset and not only if we're
> connected to an HDMI monitor.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

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

> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c | 46 +++++++++++++++++++----------------
>  1 file changed, 26 insertions(+), 20 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index 4058985940e6..00592c1ada73 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -425,6 +425,30 @@ static void vc4_hdmi_set_timings(struct vc4_hdmi *vc4_hdmi,
>                    (hsync_pos ? 0 : VC4_HD_VID_CTL_HSYNC_LOW));
>  }
>
> +static void vc4_hdmi_recenter_fifo(struct vc4_hdmi *vc4_hdmi)
> +{
> +       u32 drift;
> +       int ret;
> +
> +       drift = HDMI_READ(HDMI_FIFO_CTL);
> +       drift &= VC4_HDMI_FIFO_VALID_WRITE_MASK;
> +
> +       HDMI_WRITE(HDMI_FIFO_CTL,
> +                  drift & ~VC4_HDMI_FIFO_CTL_RECENTER);
> +       HDMI_WRITE(HDMI_FIFO_CTL,
> +                  drift | VC4_HDMI_FIFO_CTL_RECENTER);
> +       usleep_range(1000, 1100);
> +       HDMI_WRITE(HDMI_FIFO_CTL,
> +                  drift & ~VC4_HDMI_FIFO_CTL_RECENTER);
> +       HDMI_WRITE(HDMI_FIFO_CTL,
> +                  drift | VC4_HDMI_FIFO_CTL_RECENTER);
> +
> +       ret = wait_for(HDMI_READ(HDMI_FIFO_CTL) &
> +                      VC4_HDMI_FIFO_CTL_RECENTER_DONE, 1);
> +       WARN_ONCE(ret, "Timeout waiting for "
> +                 "VC4_HDMI_FIFO_CTL_RECENTER_DONE");
> +}
> +
>  static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>  {
>         struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
> @@ -543,8 +567,6 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>         }
>
>         if (vc4_encoder->hdmi_monitor) {
> -               u32 drift;
> -
>                 WARN_ON(!(HDMI_READ(HDMI_SCHEDULER_CONTROL) &
>                           VC4_HDMI_SCHEDULER_CONTROL_HDMI_ACTIVE));
>                 HDMI_WRITE(HDMI_SCHEDULER_CONTROL,
> @@ -555,25 +577,9 @@ static void vc4_hdmi_encoder_enable(struct drm_encoder *encoder)
>                            VC4_HDMI_RAM_PACKET_ENABLE);
>
>                 vc4_hdmi_set_infoframes(encoder);
> -
> -               drift = HDMI_READ(HDMI_FIFO_CTL);
> -               drift &= VC4_HDMI_FIFO_VALID_WRITE_MASK;
> -
> -               HDMI_WRITE(HDMI_FIFO_CTL,
> -                          drift & ~VC4_HDMI_FIFO_CTL_RECENTER);
> -               HDMI_WRITE(HDMI_FIFO_CTL,
> -                          drift | VC4_HDMI_FIFO_CTL_RECENTER);
> -               usleep_range(1000, 1100);
> -               HDMI_WRITE(HDMI_FIFO_CTL,
> -                          drift & ~VC4_HDMI_FIFO_CTL_RECENTER);
> -               HDMI_WRITE(HDMI_FIFO_CTL,
> -                          drift | VC4_HDMI_FIFO_CTL_RECENTER);
> -
> -               ret = wait_for(HDMI_READ(HDMI_FIFO_CTL) &
> -                              VC4_HDMI_FIFO_CTL_RECENTER_DONE, 1);
> -               WARN_ONCE(ret, "Timeout waiting for "
> -                         "VC4_HDMI_FIFO_CTL_RECENTER_DONE");
>         }
> +
> +       vc4_hdmi_recenter_fifo(vc4_hdmi);
>  }
>
>  static enum drm_mode_status
> --
> git-series 0.9.1