linux-kernel - Re: [PATCH v4 73/78] drm/vc4: hdmi: Switch to blank pixels when disabled

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Date:   Tue, 28 Jul 2020 16:09:54 +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 73/78] drm/vc4: hdmi: Switch to blank pixels when disabled

Hi Maxime

On Wed, 8 Jul 2020 at 18:44, Maxime Ripard <maxime@...no.tech> wrote:
>
> In order to avoid pixels getting stuck in an unflushable FIFO, we need when
> we disable the HDMI controller to switch away from getting our pixels from
> the pixelvalve and instead use blank pixels, and switch back to the
> pixelvalve when we enable the HDMI controller.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

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

> ---
>  drivers/gpu/drm/vc4/vc4_hdmi.c |  9 +++++++++
>  drivers/gpu/drm/vc4/vc4_regs.h |  3 +++
>  2 files changed, 12 insertions(+)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index f56a718a3643..37463b016b47 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -325,6 +325,12 @@ static void vc4_hdmi_encoder_post_crtc_disable(struct drm_encoder *encoder)
>         struct vc4_hdmi *vc4_hdmi = encoder_to_vc4_hdmi(encoder);
>
>         HDMI_WRITE(HDMI_RAM_PACKET_CONFIG, 0);
> +
> +       HDMI_WRITE(HDMI_VID_CTL, HDMI_READ(HDMI_VID_CTL) |
> +                  VC4_HD_VID_CTL_CLRRGB | VC4_HD_VID_CTL_CLRSYNC);
> +
> +       HDMI_WRITE(HDMI_VID_CTL,
> +                  HDMI_READ(HDMI_VID_CTL) | VC4_HD_VID_CTL_BLANKPIX);
>  }
>
>  static void vc4_hdmi_encoder_post_crtc_powerdown(struct drm_encoder *encoder)
> @@ -563,6 +569,9 @@ static void vc4_hdmi_encoder_post_crtc_enable(struct drm_encoder *encoder)
>                    (vsync_pos ? 0 : VC4_HD_VID_CTL_VSYNC_LOW) |
>                    (hsync_pos ? 0 : VC4_HD_VID_CTL_HSYNC_LOW));
>
> +       HDMI_WRITE(HDMI_VID_CTL,
> +                  HDMI_READ(HDMI_VID_CTL) & ~VC4_HD_VID_CTL_BLANKPIX);
> +
>         if (vc4_encoder->hdmi_monitor) {
>                 HDMI_WRITE(HDMI_SCHEDULER_CONTROL,
>                            HDMI_READ(HDMI_SCHEDULER_CONTROL) |
> diff --git a/drivers/gpu/drm/vc4/vc4_regs.h b/drivers/gpu/drm/vc4/vc4_regs.h
> index d1e8961edaa0..30af52b406f1 100644
> --- a/drivers/gpu/drm/vc4/vc4_regs.h
> +++ b/drivers/gpu/drm/vc4/vc4_regs.h
> @@ -723,6 +723,9 @@
>  # define VC4_HD_VID_CTL_FRAME_COUNTER_RESET    BIT(29)
>  # define VC4_HD_VID_CTL_VSYNC_LOW              BIT(28)
>  # define VC4_HD_VID_CTL_HSYNC_LOW              BIT(27)
> +# define VC4_HD_VID_CTL_CLRSYNC                        BIT(24)
> +# define VC4_HD_VID_CTL_CLRRGB                 BIT(23)
> +# define VC4_HD_VID_CTL_BLANKPIX               BIT(18)
>
>  # define VC4_HD_CSC_CTL_ORDER_MASK             VC4_MASK(7, 5)
>  # define VC4_HD_CSC_CTL_ORDER_SHIFT            5
> --
> git-series 0.9.1