linux-kernel - Re: [PATCH v4 31/78] drm/vc4: crtc: Clear the PixelValve FIFO during configuration

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Message-ID: <CAPY8ntDK76+3PR8kbi8gzb8n4zryDhZvhwKyGsdPb_J3Uf-ASQ@mail.gmail.com>
Date:   Tue, 28 Jul 2020 12:41:56 +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 31/78] drm/vc4: crtc: Clear the PixelValve FIFO during configuration

Hi Maxime

On Wed, 8 Jul 2020 at 18:43, Maxime Ripard <maxime@...no.tech> wrote:
>
> Even though it's not really clear why we need to flush the PV FIFO during
> the configuration even though we started by flushing it, experience shows
> that without it we get a stale pixel stuck in the FIFO between the HVS and
> the PV.
>
> Signed-off-by: Maxime Ripard <maxime@...no.tech>

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

> ---
>  drivers/gpu/drm/vc4/vc4_crtc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_crtc.c b/drivers/gpu/drm/vc4/vc4_crtc.c
> index 13fe0e370fb3..25a77cd46b28 100644
> --- a/drivers/gpu/drm/vc4/vc4_crtc.c
> +++ b/drivers/gpu/drm/vc4/vc4_crtc.c
> @@ -358,7 +358,7 @@ static void vc4_crtc_config_pv(struct drm_crtc *crtc)
>         if (is_dsi)
>                 CRTC_WRITE(PV_HACT_ACT, mode->hdisplay * pixel_rep);
>
> -       CRTC_WRITE(PV_CONTROL,
> +       CRTC_WRITE(PV_CONTROL, PV_CONTROL_FIFO_CLR |
>                    vc4_crtc_get_fifo_full_level_bits(vc4_crtc, format) |
>                    VC4_SET_FIELD(format, PV_CONTROL_FORMAT) |
>                    VC4_SET_FIELD(pixel_rep - 1, PV_CONTROL_PIXEL_REP) |
> --
> git-series 0.9.1