linux-kernel - RE: [PATCH v8 1/4] drm/msm/dp: Add eDP support via aux

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Message-ID: <MW4PR02MB718603608E45FB53A8D942C7E1F49@MW4PR02MB7186.namprd02.prod.outlook.com>
Date:   Thu, 21 Apr 2022 16:00:41 +0000
From:   "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
To:     Doug Anderson <dianders@...omium.org>,
        "Sankeerth Billakanti (QUIC)" <quic_sbillaka@...cinc.com>
CC:     dri-devel <dri-devel@...ts.freedesktop.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        freedreno <freedreno@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, Rob Clark <robdclark@...il.com>,
        Sean Paul <seanpaul@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        quic_kalyant <quic_kalyant@...cinc.com>,
        "Abhinav Kumar (QUIC)" <quic_abhinavk@...cinc.com>,
        "Kuogee Hsieh (QUIC)" <quic_khsieh@...cinc.com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        "dmitry.baryshkov@...aro.org" <dmitry.baryshkov@...aro.org>,
        quic_vproddut <quic_vproddut@...cinc.com>,
        "Aravind Venkateswaran (QUIC)" <quic_aravindh@...cinc.com>,
        Steev Klimaszewski <steev@...i.org>
Subject: RE: [PATCH v8 1/4] drm/msm/dp: Add eDP support via aux_bus

Hi Doug,

>On Thu, Apr 21, 2022 at 7:37 AM Sankeerth Billakanti
><quic_sbillaka@...cinc.com> wrote:
>>
>> @@ -1530,6 +1532,61 @@ void msm_dp_debugfs_init(struct msm_dp
>*dp_display, struct drm_minor *minor)
>>         }
>>  }
>>
>> +static int dp_display_get_next_bridge(struct msm_dp *dp) {
>> +       int rc;
>> +       struct dp_display_private *dp_priv;
>> +       struct device_node *aux_bus;
>> +       struct device *dev;
>> +
>> +       dp_priv = container_of(dp, struct dp_display_private, dp_display);
>> +       dev = &dp_priv->pdev->dev;
>> +       aux_bus = of_get_child_by_name(dev->of_node, "aux-bus");
>> +
>> +       if (aux_bus && dp->is_edp) {
>> +               dp_display_host_init(dp_priv);
>> +               dp_catalog_ctrl_hpd_config(dp_priv->catalog);
>> +               dp_display_host_phy_init(dp_priv);
>> +               enable_irq(dp_priv->irq);
>> +
>> +               rc = devm_of_dp_aux_populate_ep_devices(dp_priv->aux);
>
>I think a comment was requested above that line saying something like:
>
>/*
> * The code below assumes that the panel will finish probing
> * by the time devm_of_dp_aux_populate_ep_devices() returns.
> * This isn't a great assumption since it will fail if the
> * panel driver is probed asynchronously but is the best we
> * can do without a bigger driver reorganization.
> */
>
>

Will add the comment

>> +               of_node_put(aux_bus);
>> +               if (rc)
>> +                       goto edp_error;
>> +       } else if (dp->is_edp) {
>> +               DRM_ERROR("eDP aux_bus not found\n");
>> +               rc = -ENODEV;
>> +               goto error;
>
>This goto doesn't add much. Just leave the above like it was in v7.
>return -ENODEV w/ no goto.
>
>

Okay

>> +       }
>> +
>> +       /*
>> +        * External bridges are mandatory for eDP interfaces: one has to
>> +        * provide at least an eDP panel (which gets wrapped into panel-
>bridge).
>> +        *
>> +        * For DisplayPort interfaces external bridges are optional, so
>> +        * silently ignore an error if one is not present (-ENODEV).
>> +        */
>> +       rc = dp_parser_find_next_bridge(dp_priv->parser);
>> +       if (rc && dp->is_edp) {
>> +               DRM_ERROR("eDP: cannot find the next bridge, rc = %d\n", rc);
>> +               goto edp_error;
>> +       } else if (rc && rc != -ENODEV) {
>> +               DRM_ERROR("DP: cannot find the next bridge, rc = %d\n", rc);
>> +               goto error;
>> +       }
>
>The above wouldn't be my favorite way of doing this. Instead, I would have
>written:
>
>  if (rc) {
>    DRM_ERROR("Cannot find the next bridge, rc = %d\n", rc);
>    goto err;
>  }
>  ...
>
>err:
>  if (dp->is_edp) {
>    disable_irq(...);
>    dp_display_host_phy_exit(...);
>    dp_display_host_deinit(...);
>  }
>  return rc;
>

If rc is ENODEV for DP, then we need to return 0. Shall I add like below ?

err:
  if (dp->is_edp) {
    disable_irq(...);
    dp_display_host_phy_exit(...);
    dp_display_host_deinit(...);
  } else
        If (rc == -ENODEV)
            rc = 0;
  return rc;

>> +
>> +       dp->next_bridge = dp_priv->parser->next_bridge;
>> +
>> +       return 0;
>> +
>> +edp_error:
>> +       disable_irq(dp_priv->irq);
>> +       dp_display_host_phy_exit(dp_priv);
>> +       dp_display_host_deinit(dp_priv);
>> +error:
>> +       return rc;
>> +}
>> +
>>  int msm_dp_modeset_init(struct msm_dp *dp_display, struct drm_device
>*dev,
>>                         struct drm_encoder *encoder)  {
>
>With the above fixes, I'd be happy enough for my Reviewed-by tag with the
>expectation that continued work will happen to continue cleaning this up.
>
>
>-Doug