[RFC v4 23/25] drm: Add DRM device registered notifier

[Daniel Vetter]

On Sat, Apr 14, 2018 at 01:53:16PM +0200, Noralf Trønnes wrote:
> Add a notifier that fires when a new DRM device is registered.
> This can be used by the bootsplash client to connect to all devices.
> 
> Signed-off-by: Noralf Trønnes <noralf at tronnes.org>

So I freaked out temporarily about your usage of notifiers here. But I
think this one of the few cases where using notifiers is actually
perfectly fine. Still not sure we really want that, instead of just
hard-coding calls to the various register functions directly (and using a
dummy no-op replacement if that part isn't enabled in Kconfig).
-Daniel

> ---
>  drivers/gpu/drm/drm_drv.c | 32 ++++++++++++++++++++++++++++++++
>  include/drm/drm_drv.h     |  4 ++++
>  2 files changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c
> index 6f21bafb29be..e42ce320ad07 100644
> --- a/drivers/gpu/drm/drm_drv.c
> +++ b/drivers/gpu/drm/drm_drv.c
> @@ -31,6 +31,7 @@
>  #include <linux/module.h>
>  #include <linux/moduleparam.h>
>  #include <linux/mount.h>
> +#include <linux/notifier.h>
>  #include <linux/slab.h>
>  #include <linux/srcu.h>
>  
> @@ -79,6 +80,8 @@ static struct dentry *drm_debugfs_root;
>  
>  DEFINE_STATIC_SRCU(drm_unplug_srcu);
>  
> +static BLOCKING_NOTIFIER_HEAD(drm_dev_notifier);
> +
>  /*
>   * DRM Minors
>   * A DRM device can provide several char-dev interfaces on the DRM-Major. Each
> @@ -837,6 +840,8 @@ int drm_dev_register(struct drm_device *dev, unsigned long flags)
>  		 dev->dev ? dev_name(dev->dev) : "virtual device",
>  		 dev->primary->index);
>  
> +	blocking_notifier_call_chain(&drm_dev_notifier, 0, dev);
> +
>  	goto out_unlock;
>  
>  err_minors:
> @@ -894,6 +899,33 @@ void drm_dev_unregister(struct drm_device *dev)
>  }
>  EXPORT_SYMBOL(drm_dev_unregister);
>  
> +/**
> + * drm_dev_register_notifier - Register a notifier for new DRM devices
> + * @nb: Notifier block
> + *
> + * Register a notifier that fires when a new &drm_device is registered.
> + *
> + * Note:
> + * Users of this function has to be linked into drm.ko. This is done to make
> + * life simple avoiding tricky race situations.
> + */
> +void drm_dev_register_notifier(struct notifier_block *nb)
> +{
> +	/* Currently this can't fail, but catch it in case this changes */
> +	WARN_ON(blocking_notifier_chain_register(&drm_dev_notifier, nb));
> +}
> +
> +/**
> + * drm_dev_unregister_notifier - Unregister DRM device notifier
> + * @nb: Notifier block
> + *
> + * This is a no-op if the notifier isn't registered.
> + */
> +void drm_dev_unregister_notifier(struct notifier_block *nb)
> +{
> +	blocking_notifier_chain_unregister(&drm_dev_notifier, nb);
> +}
> +
>  /**
>   * drm_dev_set_unique - Set the unique name of a DRM device
>   * @dev: device of which to set the unique name
> diff --git a/include/drm/drm_drv.h b/include/drm/drm_drv.h
> index 13356e6fd40c..5e6c6ed0d59d 100644
> --- a/include/drm/drm_drv.h
> +++ b/include/drm/drm_drv.h
> @@ -40,6 +40,7 @@ struct drm_minor;
>  struct dma_buf_attachment;
>  struct drm_display_mode;
>  struct drm_mode_create_dumb;
> +struct notifier_block;
>  struct drm_printer;
>  
>  /* driver capabilities and requirements mask */
> @@ -641,6 +642,9 @@ struct drm_device *drm_dev_alloc(struct drm_driver *driver,
>  int drm_dev_register(struct drm_device *dev, unsigned long flags);
>  void drm_dev_unregister(struct drm_device *dev);
>  
> +void drm_dev_register_notifier(struct notifier_block *nb);
> +void drm_dev_unregister_notifier(struct notifier_block *nb);
> +
>  void drm_dev_get(struct drm_device *dev);
>  void drm_dev_put(struct drm_device *dev);
>  void drm_dev_unref(struct drm_device *dev);
> -- 
> 2.15.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch