linux-kernel - Re: [PATCH v2] drm/bridge: parade-ps8640: Link device to ensure suspend/resume order

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Date:   Wed, 5 Jan 2022 18:33:58 +0100
From:   Robert Foss <robert.foss@...aro.org>
To:     AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...labora.com>
Cc:     a.hajda@...sung.com, narmstrong@...libre.com,
        laurent.pinchart@...asonboard.com, jonas@...boo.se,
        jernej.skrabec@...il.com, airlied@...ux.ie, daniel@...ll.ch,
        dri-devel@...ts.freedesktop.org, kernel@...labora.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] drm/bridge: parade-ps8640: Link device to ensure
 suspend/resume order

On Wed, 5 Jan 2022 at 10:08, AngeloGioacchino Del Regno
<angelogioacchino.delregno@...labora.com> wrote:
>
> Entering suspend while the display attached to this bridge is still on
> makes the resume sequence to resume the bridge first, display last:
> when this happens, we get a timeout while resuming the bridge, as its
> MCU will get stuck due to the display being unpowered.
>
> On the other hand, on mt8173-elm, closing the lid makes the display to
> get powered off first, bridge last, so at resume time the sequence is
> swapped (compared to the first example) and everything just works
> as expected.
>
> Add a stateless device link to the DRM device that this bridge belongs
> to, ensuring a correct resume sequence and solving the unability to
> correctly resume bridge operation in the first mentioned example.
>
> Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>
> ---
>  drivers/gpu/drm/bridge/parade-ps8640.c | 27 ++++++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index 818704bf5e86..450bc9bdf295 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -102,6 +102,7 @@ struct ps8640 {
>         struct regulator_bulk_data supplies[2];
>         struct gpio_desc *gpio_reset;
>         struct gpio_desc *gpio_powerdown;
> +       struct device_link *link;
>         bool pre_enabled;
>  };
>
> @@ -456,14 +457,36 @@ static int ps8640_bridge_attach(struct drm_bridge *bridge,
>                 return ret;
>         }
>
> +       ps_bridge->link = device_link_add(bridge->dev->dev, dev, DL_FLAG_STATELESS);
> +       if (!ps_bridge->link) {
> +               dev_err(dev, "failed to create device link");
> +               ret = -EINVAL;
> +               goto err_devlink;
> +       }
> +
>         /* Attach the panel-bridge to the dsi bridge */
> -       return drm_bridge_attach(bridge->encoder, ps_bridge->panel_bridge,
> +       ret = drm_bridge_attach(bridge->encoder, ps_bridge->panel_bridge,
>                                  &ps_bridge->bridge, flags);

Bad alignment according to checkpatch --strict

> +       if (ret)
> +               goto err_bridge_attach;
> +
> +       return 0;
> +
> +err_bridge_attach:
> +       device_link_del(ps_bridge->link);
> +err_devlink:
> +       drm_dp_aux_unregister(&ps_bridge->aux);
> +
> +       return ret;
>  }
>
>  static void ps8640_bridge_detach(struct drm_bridge *bridge)
>  {
> -       drm_dp_aux_unregister(&bridge_to_ps8640(bridge)->aux);
> +       struct ps8640 *ps_bridge = bridge_to_ps8640(bridge);
> +
> +       drm_dp_aux_unregister(&ps_bridge->aux);
> +       if (ps_bridge->link)
> +               device_link_del(ps_bridge->link);
>  }
>
>  static struct edid *ps8640_bridge_get_edid(struct drm_bridge *bridge,
> --
> 2.33.1
>

Fixed alignment issue, applied to drm-misc-next and added r-b tag.

Reviewed-by: Robert Foss <robert.foss@...aro.org>