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From:   Chun-Kuang Hu <chunkuang.hu@kernel.org>
Date:   Thu, 27 Jan 2022 23:21:27 +0800
Message-ID: <CAAOTY__yO6Cq8qt8RSh9AX68mJEv+wWvuhY0_p-PTJ=eJD_7aA@mail.gmail.com>
Subject: Re: [PATCH v3] drm/mediatek: mtk_dsi: Avoid EPROBE_DEFER loop with
 external bridge
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@collabora.com>
Cc:     DRI Development <dri-devel@lists.freedesktop.org>,
        Chun-Kuang Hu <chunkuang.hu@kernel.org>,
        David Airlie <airlied@linux.ie>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        andrzej.hajda@intel.com,
        "moderated list:ARM/Mediatek SoC support" 
        <linux-mediatek@lists.infradead.org>,
        Jagan Teki <jagan@amarulasolutions.com>,
        Matthias Brugger <matthias.bgg@gmail.com>,
        Collabora Kernel ML <kernel@collabora.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>
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Hi, Angelo:

AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com> =E6=96=
=BC
2022=E5=B9=B41=E6=9C=8827=E6=97=A5 =E9=80=B1=E5=9B=9B =E4=B8=8B=E5=8D=8810:=
36=E5=AF=AB=E9=81=93=EF=BC=9A
>
> DRM bridge drivers are now attaching their DSI device at probe time,
> which requires us to register our DSI host in order to let the bridge
> to probe: this recently started producing an endless -EPROBE_DEFER
> loop on some machines that are using external bridges, like the
> parade-ps8640, found on the ACER Chromebook R13.
>
> Now that the DSI hosts/devices probe sequence is documented, we can
> do adjustments to the mtk_dsi driver as to both fix now and make sure
> to avoid this situation in the future: for this, following what is
> documented in drm_bridge.c, move the mtk_dsi component_add() to the
> mtk_dsi_ops.attach callback and delete it in the detach callback;
> keeping in mind that we are registering a drm_bridge for our DSI,
> which is only used/attached if the DSI Host is bound, it wouldn't
> make sense to keep adding our bridge at probe time (as it would
> be useless to have it if mtk_dsi_ops.attach() fails!), so also move
> that one to the dsi host attach function (and remove it in detach).
>
> Fixes: 209264a85707 ("drm/bridge: Document the probe issue with MIPI-DSI =
bridges")

The fixed tag should indicate the patch which cause the bug, but why a
patch just adding document would cause bug?
So no any patch cause bug? This patch just want to prevent a possible bug?

Regards,
Chun-Kuang.

> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@coll=
abora.com>
> Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
> Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
>
> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 167 +++++++++++++++--------------
>  1 file changed, 84 insertions(+), 83 deletions(-)
>
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediate=
k/mtk_dsi.c
> index 5d90d2eb0019..bced4c7d668e 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -786,18 +786,101 @@ void mtk_dsi_ddp_stop(struct device *dev)
>         mtk_dsi_poweroff(dsi);
>  }
>
> +static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *=
dsi)
> +{
> +       int ret;
> +
> +       ret =3D drm_simple_encoder_init(drm, &dsi->encoder,
> +                                     DRM_MODE_ENCODER_DSI);
> +       if (ret) {
> +               DRM_ERROR("Failed to encoder init to drm\n");
> +               return ret;
> +       }
> +
> +       dsi->encoder.possible_crtcs =3D mtk_drm_find_possible_crtc_by_com=
p(drm, dsi->host.dev);
> +
> +       ret =3D drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
> +                               DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> +       if (ret)
> +               goto err_cleanup_encoder;
> +
> +       dsi->connector =3D drm_bridge_connector_init(drm, &dsi->encoder);
> +       if (IS_ERR(dsi->connector)) {
> +               DRM_ERROR("Unable to create bridge connector\n");
> +               ret =3D PTR_ERR(dsi->connector);
> +               goto err_cleanup_encoder;
> +       }
> +       drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
> +
> +       return 0;
> +
> +err_cleanup_encoder:
> +       drm_encoder_cleanup(&dsi->encoder);
> +       return ret;
> +}
> +
> +static int mtk_dsi_bind(struct device *dev, struct device *master, void =
*data)
> +{
> +       int ret;
> +       struct drm_device *drm =3D data;
> +       struct mtk_dsi *dsi =3D dev_get_drvdata(dev);
> +
> +       ret =3D mtk_dsi_encoder_init(drm, dsi);
> +       if (ret)
> +               return ret;
> +
> +       return device_reset_optional(dev);
> +}
> +
> +static void mtk_dsi_unbind(struct device *dev, struct device *master,
> +                          void *data)
> +{
> +       struct mtk_dsi *dsi =3D dev_get_drvdata(dev);
> +
> +       drm_encoder_cleanup(&dsi->encoder);
> +}
> +
> +static const struct component_ops mtk_dsi_component_ops =3D {
> +       .bind =3D mtk_dsi_bind,
> +       .unbind =3D mtk_dsi_unbind,
> +};
> +
>  static int mtk_dsi_host_attach(struct mipi_dsi_host *host,
>                                struct mipi_dsi_device *device)
>  {
>         struct mtk_dsi *dsi =3D host_to_dsi(host);
> +       struct device *dev =3D host->dev;
> +       int ret;
>
>         dsi->lanes =3D device->lanes;
>         dsi->format =3D device->format;
>         dsi->mode_flags =3D device->mode_flags;
> +       dsi->next_bridge =3D devm_drm_of_get_bridge(dev, dev->of_node, 0,=
 0);
> +       if (IS_ERR(dsi->next_bridge))
> +               return PTR_ERR(dsi->next_bridge);
> +
> +       drm_bridge_add(&dsi->bridge);
> +
> +       ret =3D component_add(host->dev, &mtk_dsi_component_ops);
> +       if (ret) {
> +               DRM_ERROR("failed to add dsi_host component: %d\n", ret);
> +               drm_bridge_remove(&dsi->bridge);
> +               return ret;
> +       }
>
>         return 0;
>  }
>
> +static int mtk_dsi_host_detach(struct mipi_dsi_host *host,
> +                              struct mipi_dsi_device *device)
> +{
> +       struct mtk_dsi *dsi =3D host_to_dsi(host);
> +
> +       component_del(host->dev, &mtk_dsi_component_ops);
> +       drm_bridge_remove(&dsi->bridge);
> +       return 0;
> +}
> +
>  static void mtk_dsi_wait_for_idle(struct mtk_dsi *dsi)
>  {
>         int ret;
> @@ -938,73 +1021,14 @@ static ssize_t mtk_dsi_host_transfer(struct mipi_d=
si_host *host,
>
>  static const struct mipi_dsi_host_ops mtk_dsi_ops =3D {
>         .attach =3D mtk_dsi_host_attach,
> +       .detach =3D mtk_dsi_host_detach,
>         .transfer =3D mtk_dsi_host_transfer,
>  };
>
> -static int mtk_dsi_encoder_init(struct drm_device *drm, struct mtk_dsi *=
dsi)
> -{
> -       int ret;
> -
> -       ret =3D drm_simple_encoder_init(drm, &dsi->encoder,
> -                                     DRM_MODE_ENCODER_DSI);
> -       if (ret) {
> -               DRM_ERROR("Failed to encoder init to drm\n");
> -               return ret;
> -       }
> -
> -       dsi->encoder.possible_crtcs =3D mtk_drm_find_possible_crtc_by_com=
p(drm, dsi->host.dev);
> -
> -       ret =3D drm_bridge_attach(&dsi->encoder, &dsi->bridge, NULL,
> -                               DRM_BRIDGE_ATTACH_NO_CONNECTOR);
> -       if (ret)
> -               goto err_cleanup_encoder;
> -
> -       dsi->connector =3D drm_bridge_connector_init(drm, &dsi->encoder);
> -       if (IS_ERR(dsi->connector)) {
> -               DRM_ERROR("Unable to create bridge connector\n");
> -               ret =3D PTR_ERR(dsi->connector);
> -               goto err_cleanup_encoder;
> -       }
> -       drm_connector_attach_encoder(dsi->connector, &dsi->encoder);
> -
> -       return 0;
> -
> -err_cleanup_encoder:
> -       drm_encoder_cleanup(&dsi->encoder);
> -       return ret;
> -}
> -
> -static int mtk_dsi_bind(struct device *dev, struct device *master, void =
*data)
> -{
> -       int ret;
> -       struct drm_device *drm =3D data;
> -       struct mtk_dsi *dsi =3D dev_get_drvdata(dev);
> -
> -       ret =3D mtk_dsi_encoder_init(drm, dsi);
> -       if (ret)
> -               return ret;
> -
> -       return device_reset_optional(dev);
> -}
> -
> -static void mtk_dsi_unbind(struct device *dev, struct device *master,
> -                          void *data)
> -{
> -       struct mtk_dsi *dsi =3D dev_get_drvdata(dev);
> -
> -       drm_encoder_cleanup(&dsi->encoder);
> -}
> -
> -static const struct component_ops mtk_dsi_component_ops =3D {
> -       .bind =3D mtk_dsi_bind,
> -       .unbind =3D mtk_dsi_unbind,
> -};
> -
>  static int mtk_dsi_probe(struct platform_device *pdev)
>  {
>         struct mtk_dsi *dsi;
>         struct device *dev =3D &pdev->dev;
> -       struct drm_panel *panel;
>         struct resource *regs;
>         int irq_num;
>         int ret;
> @@ -1021,19 +1045,6 @@ static int mtk_dsi_probe(struct platform_device *p=
dev)
>                 return ret;
>         }
>
> -       ret =3D drm_of_find_panel_or_bridge(dev->of_node, 0, 0,
> -                                         &panel, &dsi->next_bridge);
> -       if (ret)
> -               goto err_unregister_host;
> -
> -       if (panel) {
> -               dsi->next_bridge =3D devm_drm_panel_bridge_add(dev, panel=
);
> -               if (IS_ERR(dsi->next_bridge)) {
> -                       ret =3D PTR_ERR(dsi->next_bridge);
> -                       goto err_unregister_host;
> -               }
> -       }
> -
>         dsi->driver_data =3D of_device_get_match_data(dev);
>
>         dsi->engine_clk =3D devm_clk_get(dev, "engine");
> @@ -1098,14 +1109,6 @@ static int mtk_dsi_probe(struct platform_device *p=
dev)
>         dsi->bridge.of_node =3D dev->of_node;
>         dsi->bridge.type =3D DRM_MODE_CONNECTOR_DSI;
>
> -       drm_bridge_add(&dsi->bridge);
> -
> -       ret =3D component_add(&pdev->dev, &mtk_dsi_component_ops);
> -       if (ret) {
> -               dev_err(&pdev->dev, "failed to add component: %d\n", ret)=
;
> -               goto err_unregister_host;
> -       }
> -
>         return 0;
>
>  err_unregister_host:
> @@ -1118,8 +1121,6 @@ static int mtk_dsi_remove(struct platform_device *p=
dev)
>         struct mtk_dsi *dsi =3D platform_get_drvdata(pdev);
>
>         mtk_output_dsi_disable(dsi);
> -       drm_bridge_remove(&dsi->bridge);
> -       component_del(&pdev->dev, &mtk_dsi_component_ops);
>         mipi_dsi_host_unregister(&dsi->host);
>
>         return 0;
> --
> 2.33.1
>