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References: <20190109133644.27459-1-narmstrong@baylibre.com>
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From:   Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Date:   Wed, 9 Jan 2019 23:18:40 +0100
Message-ID: <CAFBinCAGGDx_9g3Y16fczUPGaBC0Ep=ULkY__n3WdrQRnDSsyA@mail.gmail.com>
Subject: Re: [PATCH] drm/meson: Fix atomic mode switching regression
To:     Neil Armstrong <narmstrong@baylibre.com>
Cc:     daniel@ffwll.ch, linux-amlogic@lists.infradead.org,
        linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org
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Hi Neil,

On Wed, Jan 9, 2019 at 2:36 PM Neil Armstrong <narmstrong@baylibre.com> wrote:
>
> Since commit 2bcd3ecab773 when switching mode from X11 (ubuntu mate for
> example) the display gets blurry, looking like an invalid framebuffer width.
>
> This commit fixed atomic crtc modesetting but didn't update the display
> parameters when changing mode, but only when starting a mode setting after
> a crtc disable.
>
> This commit setups the crctc parameter in _begin() and _enable() to
> take in account the current ctrc parameters.
>
> Reported-by: Tony McKahan <tonymckahan@gmail.com>
> Fixes: 2bcd3ecab773 ("drm/meson: Fixes for drm_crtc_vblank_on/off support")
> Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
> ---
>  drivers/gpu/drm/meson/meson_crtc.c | 16 +++++++++++++---
>  1 file changed, 13 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/gpu/drm/meson/meson_crtc.c b/drivers/gpu/drm/meson/meson_crtc.c
> index 75d97f1b2e8f..5bb432021caf 100644
> --- a/drivers/gpu/drm/meson/meson_crtc.c
> +++ b/drivers/gpu/drm/meson/meson_crtc.c
> @@ -82,14 +82,12 @@ static const struct drm_crtc_funcs meson_crtc_funcs = {
>
>  };
>
> -static void meson_crtc_enable(struct drm_crtc *crtc)
> +static void meson_crtc_setup(struct drm_crtc *crtc)
>  {
>         struct meson_crtc *meson_crtc = to_meson_crtc(crtc);
>         struct drm_crtc_state *crtc_state = crtc->state;
>         struct meson_drm *priv = meson_crtc->priv;
>
> -       DRM_DEBUG_DRIVER("\n");
> -
>         if (!crtc_state) {
>                 DRM_ERROR("Invalid crtc_state\n");
>                 return;
> @@ -98,6 +96,16 @@ static void meson_crtc_enable(struct drm_crtc *crtc)
>         /* Enable VPP Postblend */
nit-pick: this "enable" comment is now in meson_crtc_setup().
I would drop it because my interpretation of the following lines is
now "setting VPP_POSTBLEND_H_SIZE enables the VPP postblend"

>         writel(crtc_state->mode.hdisplay,
>                priv->io_base + _REG(VPP_POSTBLEND_H_SIZE));
> +}
> +
> +static void meson_crtc_enable(struct drm_crtc *crtc)
> +{
> +       struct meson_crtc *meson_crtc = to_meson_crtc(crtc);
> +       struct meson_drm *priv = meson_crtc->priv;
> +
> +       DRM_DEBUG_DRIVER("\n");
> +
> +       meson_crtc_setup(crtc);
>
>         /* VD1 Preblend vertical start/end */
>         writel(FIELD_PREP(GENMASK(11, 0), 2303),
> @@ -121,6 +129,8 @@ static void meson_crtc_atomic_enable(struct drm_crtc *crtc,
>
>         if (!meson_crtc->enabled)
>                 meson_crtc_enable(crtc);
> +       else
> +               meson_crtc_setup(crtc);
it's probably only personal preference, but have you thought about
re-ordering this:
  meson_crtc_setup(crtc);

  if (!meson_crtc->enabled)
    meson_crtc_enable(crtc);

with that you could get rid of the meson_crtc_setup() call in
meson_crtc_enable(), leaving only one code-path (instead of two) which
calls meson_crtc_setup()


Regards
Martin