linux-kernel - Re: [PATCH v8 1/3] gpu: drm: separate panel orientation property creating and value setting

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Date:   Tue, 15 Feb 2022 21:08:16 +0800
From:   Hsin-Yi Wang <hsinyi@...omium.org>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     dri-devel@...ts.freedesktop.org, David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>, amd-gfx@...ts.freedesktop.org,
        intel-gfx@...ts.freedesktop.org,
        Chun-Kuang Hu <chunkuang.hu@...nel.org>,
        Sean Paul <sean@...rly.run>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org, Rob Herring <robh+dt@...nel.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-mediatek@...ts.infradead.org,
        Simon Ser <contact@...rsion.fr>,
        Harry Wentland <harry.wentland@....com>,
        Alex Deucher <alexander.deucher@....com>,
        Jani Nikula <jani.nikula@...ux.intel.com>
Subject: Re: [PATCH v8 1/3] gpu: drm: separate panel orientation property
 creating and value setting

On Tue, Feb 15, 2022 at 12:03 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Hsin-Yi Wang <hsinyi@...omium.org> writes:
>
> > On Tue, Feb 15, 2022 at 9:17 AM Gabriel Krisman Bertazi
> > <krisman@...labora.com> wrote:
> >>
> >> Hsin-Yi Wang <hsinyi@...omium.org> writes:
> >>
> >> > drm_dev_register() sets connector->registration_state to
> >> > DRM_CONNECTOR_REGISTERED and dev->registered to true. If
> >> > drm_connector_set_panel_orientation() is first called after
> >> > drm_dev_register(), it will fail several checks and results in following
> >> > warning.
> >>
> >> Hi,
> >>
> >> I stumbled upon this when investigating the same WARN_ON on amdgpu.
> >> Thanks for the patch :)
> >>
> >> > diff --git a/drivers/gpu/drm/drm_connector.c b/drivers/gpu/drm/drm_connector.c
> >> > index a50c82bc2b2fec..572ead7ac10690 100644
> >> > --- a/drivers/gpu/drm/drm_connector.c
> >> > +++ b/drivers/gpu/drm/drm_connector.c
> >> > @@ -1252,7 +1252,7 @@ static const struct drm_prop_enum_list dp_colorspaces[] = {
> >> >   *   INPUT_PROP_DIRECT) will still map 1:1 to the actual LCD panel
> >> >   *   coordinates, so if userspace rotates the picture to adjust for
> >> >   *   the orientation it must also apply the same transformation to the
> >> > - *   touchscreen input coordinates. This property is initialized by calling
> >> > + *   touchscreen input coordinates. This property value is set by calling
> >> >   *   drm_connector_set_panel_orientation() or
> >> >   *   drm_connector_set_panel_orientation_with_quirk()
> >> >   *
> >> > @@ -2341,8 +2341,8 @@ EXPORT_SYMBOL(drm_connector_set_vrr_capable_property);
> >> >   * @connector: connector for which to set the panel-orientation property.
> >> >   * @panel_orientation: drm_panel_orientation value to set
> >> >   *
> >> > - * This function sets the connector's panel_orientation and attaches
> >> > - * a "panel orientation" property to the connector.
> >> > + * This function sets the connector's panel_orientation value. If the property
> >> > + * doesn't exist, it will try to create one.
> >> >   *
> >> >   * Calling this function on a connector where the panel_orientation has
> >> >   * already been set is a no-op (e.g. the orientation has been overridden with
> >> > @@ -2373,19 +2373,12 @@ int drm_connector_set_panel_orientation(
> >> >       info->panel_orientation = panel_orientation;
> >> >
> >> >       prop = dev->mode_config.panel_orientation_property;
> >> > -     if (!prop) {
> >> > -             prop = drm_property_create_enum(dev, DRM_MODE_PROP_IMMUTABLE,
> >> > -                             "panel orientation",
> >> > -                             drm_panel_orientation_enum_list,
> >> > -                             ARRAY_SIZE(drm_panel_orientation_enum_list));
> >> > -             if (!prop)
> >> > -                     return -ENOMEM;
> >> > -
> >> > -             dev->mode_config.panel_orientation_property = prop;
> >> > -     }
> >> > +     if (!prop &&
> >> > +         drm_connector_init_panel_orientation_property(connector) < 0)
> >> > +             return -ENOMEM;
> >> >
> >>
> >> In the case where the property has not been created beforehand, you
> >> forgot to reinitialize prop here, after calling
> >> drm_connector_init_panel_orientation_property().  This means
> > hi Gabriel,
> >
> > drm_connector_init_panel_orientation_property() will create prop if
> > it's null. If prop fails to be created there, it will return -ENOMEM.
>
> Yes.  But *after the property is successfully created*, the prop variable is still
> NULL.  And then you call the following, using prop, which is still NULL:
>
> >> > +     drm_object_property_set_value(&connector->base, prop,
> >> > +                                   info->panel_orientation);
>
> This will do property->dev right on the first line of code, and dereference the
> null prop pointer.

Ah, right. Sorry that I totally missed this.
I'll fix it in the next version if the idea of this patch is accepted.
There might be another preferred solution for this.

>
> You must do
>
>   prop = dev->mode_config.panel_orientation_property;
>
> again after drm_connector_init_panel_orientation_property successfully
> returns, or call drm_object_property_set_value using
> dev->mode_config.panel_orientation_property directly:
>
>   drm_object_property_set_value(&connector->base,
>                         dev->mode_config.panel_orientation_property
>                         info->panel_orientation);
>
> --
> Gabriel Krisman Bertazi