[PATCH v2 34/34] drm/bridge: panel: convert to devm_drm_bridge_alloc() API

[Maxime Ripard]

On Mon, Apr 28, 2025 at 05:25:16PM +0200, Luca Ceresoli wrote:
> Hi Maxime,
> 
> On Mon, 28 Apr 2025 13:39:23 +0200
> Maxime Ripard <mripard at kernel.org> wrote:
> 
> > On Thu, Apr 24, 2025 at 10:05:49PM +0200, Luca Ceresoli wrote:
> > > This is the new API for allocating DRM bridges.
> > > 
> > > The devm lifetime management of this driver is peculiar. The underlying
> > > device for the panel_bridge is the panel, and the devm lifetime is tied the
> > > panel device (panel->dev). However the panel_bridge allocation is not
> > > performed by the panel driver, but rather by a separate entity (typically
> > > the previous bridge in the encoder chain).
> > > 
> > > Thus when that separate entoty is destroyed, the panel_bridge is not
> > > removed automatically by devm, so it is rather done explicitly by calling
> > > drm_panel_bridge_remove(). This is the function that does devm_kfree() the
> > > panel_bridge in current code, so update it as well to put the bridge
> > > reference instead.
> > > 
> > > Signed-off-by: Luca Ceresoli <luca.ceresoli at bootlin.com>  
> > 
> > This looks fine, but we need a TODO entry to clean this up later on, and
> > a comment on devm_drm_put_bridge that this is inherently unsafe and
> > must not be used.
> 
> Ah, I see, OK.
> 
> Quick draft:
> 
>  /**
>   * devm_drm_put_bridge - Release a bridge reference obtained via devm
>   * @dev: device that got the bridge via devm
>   * @bridge: pointer to a struct drm_bridge obtained via devm
>   *
>   * Same as drm_bridge_put() for bridge pointers obtained via devm functions
>   * such as devm_drm_bridge_alloc().
> + *
> + * This function is a temporary workaround and MUST NOT be used. Manual
> + * handling of bridge lifetime is inherently unsafe.
>   */

That part looks good to me

> and:
> 
> -	devm_kfree(panel_bridge->panel->dev, bridge);
> +       /* TODO remove this after reworking panel_bridge lifetime */
> +	devm_drm_put_bridge(panel_bridge->panel->dev, bridge);
>  }
> 
> Does it look good enough?

That too, but I was talking about an entry in
https://www.kernel.org/doc/html/latest/gpu/todo.html

Maxime
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 273 bytes
Desc: not available
URL: <https://lists.freedesktop.org/archives/dri-devel/attachments/20250505/5791284c/attachment.sig>