Re: [PATCH] drm/bridge: introduce bridge detaching mechanism

[Daniel Vetter <daniel@ffwll.ch>]

On Tue, Aug 23, 2016 at 04:10:04PM +0200, Andrea Merello wrote:
> Up to now, once a bridge has been attached to a DRM device, it cannot
> be undone.
> 
> In particular you couldn't rmmod/insmod a DRM driver that uses a bridge,
> because the bridge would remain bound to the first (dead) driver instance.
> 
> This patch fixes this by introducing drm_encoder_detach() and a ->detach
> callback in drm_bridge_funcs for the bridge to be notified about detaches.
> 
> It's DRM/KMS driver responsibility to call drm_encoder_detach().
> 
> Suggested-by: Daniel Vetter <daniel@ffwll.ch>
> Suggested-by: Lucas Stach <l.stach@pengutronix.de>
> Signed-off-by: Andrea Merello <andrea.merello@gmail.com>
> Cc: Archit Taneja <architt@codeaurora.org>
> Cc: David Airlie <airlied@linux.ie>
> Cc: Daniel Vetter <daniel@ffwll.ch>
> Cc: Lucas Stach <l.stach@pengutronix.de>
> 
> diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c
> index 2555430..c4ace90 100644
> --- a/drivers/gpu/drm/drm_bridge.c
> +++ b/drivers/gpu/drm/drm_bridge.c
> @@ -125,6 +125,39 @@ int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge)
>  EXPORT_SYMBOL(drm_bridge_attach);
> 
>  /**
> + * drm_bridge_detach - deassociate given bridge from its DRM device
> + *
> + * @bridge: bridge control structure
> + *
> + * called by a kms driver to unlink one of our encoder/bridge to the given
> + * bridge.
> + *
> + * Note that tearing down links between the bridge and our encoder/bridge
> + * objects needs to be handled by the kms driver itself
> + *
> + * RETURNS:
> + * Zero on success, error code on failure
> + */
> +int drm_bridge_detach(struct drm_bridge *bridge)

Generally detach/cleanup functions have a return type of void - there's no
way (usually) to bail out on errors anyway.

> +{
> +	int ret;
> +
> +	if (!bridge || !bridge->dev)

Hence WARN_ON here probably.

> +		return -EINVAL;
> +
> +	if (bridge->funcs->detach) {
> +		ret = bridge->funcs->detach(bridge);

Same for the callback to the backend.
> +		if (ret)
> +			return ret;
> +	}
> +
> +	bridge->dev = NULL;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_bridge_detach);
> +
> +/**
>   * DOC: bridge callbacks
>   *
>   * The &drm_bridge_funcs ops are populated by the bridge driver. The DRM
> diff --git a/include/drm/drm_crtc.h b/include/drm/drm_crtc.h
> index b618b50..eef4db8 100644
> --- a/include/drm/drm_crtc.h
> +++ b/include/drm/drm_crtc.h
> @@ -1766,6 +1766,7 @@ struct drm_plane {
>   */
>  struct drm_bridge_funcs {
>  	int (*attach)(struct drm_bridge *bridge);
> +	int (*detach)(struct drm_bridge *bridge);

kerneldoc for @detach is missing here. And I think it'd be good to also
make the kerneldoc for @attach a stand-alone comment and flesh it out a
bit.

You might also need to include this into the simple pipe series so that
you can wire up detach support for those helpers too.

Otherwise looks all good I think.

Thanks, Daniel

> 
>  	/**
>  	 * @mode_fixup:
> @@ -3196,6 +3197,7 @@ extern int drm_bridge_add(struct drm_bridge *bridge);
>  extern void drm_bridge_remove(struct drm_bridge *bridge);
>  extern struct drm_bridge *of_drm_find_bridge(struct device_node *np);
>  extern int drm_bridge_attach(struct drm_device *dev, struct drm_bridge *bridge);
> +extern int drm_bridge_detach(struct drm_bridge *bridge);
> 
>  bool drm_bridge_mode_fixup(struct drm_bridge *bridge,
>  			const struct drm_display_mode *mode,
> --
> 2.7.4

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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