Re: [RFC v4 21/25] drm/fb-helper: Add drm_fb_helper_fb_open/release()

[Daniel Vetter <daniel@ffwll.ch>]

On Sat, Apr 14, 2018 at 01:53:14PM +0200, Noralf Trønnes wrote:
> These helpers keep track of fbdev users and drm_driver.last_close will
> only restore fbdev when actually in use. Additionally the display is
> turned off when the last user is closing. fbcon is a user in this context.
> 
> If struct fb_ops is defined in a library, fb_open() takes a ref on the
> library (fb_ops.owner) instead of the driver module. Fix that by ensuring
> that the driver module is pinned.
> 
> The functions are not added to the DRM_FB_HELPER_DEFAULT_OPS() macro,
> because some of its users do set fb_open/release themselves.
> 
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> ---
>  drivers/gpu/drm/drm_fb_helper.c | 54 ++++++++++++++++++++++++++++++++++++++++-
>  include/drm/drm_fb_helper.h     | 29 ++++++++++++++++++++++
>  2 files changed, 82 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 98e5bc92c9f2..b1124c08b1ed 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -177,7 +177,7 @@ int drm_fb_helper_restore_fbdev_mode_unlocked(struct drm_fb_helper *fb_helper)
>  	if (!drm_fbdev_emulation || !fb_helper)
>  		return -ENODEV;
>  
> -	if (READ_ONCE(fb_helper->deferred_setup))
> +	if (READ_ONCE(fb_helper->deferred_setup) || !READ_ONCE(fb_helper->open_count))
>  		return 0;
>  
>  	mutex_lock(&fb_helper->lock);
> @@ -368,6 +368,7 @@ void drm_fb_helper_prepare(struct drm_device *dev, struct drm_fb_helper *helper,
>  	INIT_WORK(&helper->dirty_work, drm_fb_helper_dirty_work);
>  	helper->dirty_clip.x1 = helper->dirty_clip.y1 = ~0;
>  	mutex_init(&helper->lock);
> +	helper->open_count = 1;
>  	helper->funcs = funcs;
>  	helper->dev = dev;
>  }
> @@ -620,6 +621,53 @@ int drm_fb_helper_defio_init(struct drm_fb_helper *fb_helper)
>  }
>  EXPORT_SYMBOL(drm_fb_helper_defio_init);
>  
> +/**
> + * drm_fb_helper_fb_open - implementation for &fb_ops.fb_open
> + * @info: fbdev registered by the helper
> + * @user: 1=userspace, 0=fbcon
> + *
> + * Increase fbdev use count.
> + * If &fb_ops is wrapped in a library, pin the driver module.
> + */
> +int drm_fb_helper_fb_open(struct fb_info *info, int user)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +
> +	if (info->fbops->owner != dev->driver->fops->owner) {
> +		if (!try_module_get(dev->driver->fops->owner))
> +			return -ENODEV;
> +	}
> +
> +	fb_helper->open_count++;
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_fb_open);
> +
> +/**
> + * drm_fb_helper_fb_release - implementation for &fb_ops.fb_release
> + * @info: fbdev registered by the helper
> + * @user: 1=userspace, 0=fbcon
> + *
> + * Decrease fbdev use count and turn off if there are no users left.
> + * If &fb_ops is wrapped in a library, unpin the driver module.
> + */
> +int drm_fb_helper_fb_release(struct fb_info *info, int user)
> +{
> +	struct drm_fb_helper *fb_helper = info->par;
> +	struct drm_device *dev = fb_helper->dev;
> +
> +	if (!(--fb_helper->open_count))
> +		drm_fb_helper_dpms(info, DRM_MODE_DPMS_OFF);
> +
> +	if (info->fbops->owner != dev->driver->fops->owner)
> +		module_put(dev->driver->fops->owner);
> +
> +	return 0;
> +}
> +EXPORT_SYMBOL(drm_fb_helper_fb_release);
> +
>  /**
>   * drm_fb_helper_sys_read - wrapper around fb_sys_read
>   * @info: fb_info struct pointer
> @@ -1436,6 +1484,10 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper,
>  	if (ret < 0)
>  		return ret;
>  
> +	/* Block restore without users if we do track it */
> +	if (fb_helper->fbdev->fbops->fb_open == drm_fb_helper_fb_open)
> +		fb_helper->open_count = 0;

Since we kzcalloc, isn't this entirely redundant? Looks confusing to me at
least.

Otherwise looks all reasonable.
-Daniel


> +
>  	strcpy(fb_helper->fb->comm, "[fbcon]");
>  	return 0;
>  }
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index 5f66f253a97b..330983975d5e 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -184,6 +184,22 @@ struct drm_fb_helper {
>  	 * See also: @deferred_setup
>  	 */
>  	int preferred_bpp;
> +
> +	/**
> +	 * @open_count:
> +	 *
> +	 * Keeps track of fbdev use to know when to not restore fbdev and to
> +	 * disable the pipeline when the last user is gone.
> +	 *
> +	 * Drivers that use drm_fb_helper_fb_open() as their \.fb_open
> +	 * callback will get an initial value of 0 and get restore based on
> +	 * actual use. Others will get an initial value of 1 which means that
> +	 * fbdev will always be restored. Drivers that call
> +	 * drm_fb_helper_fb_open() in their \.fb_open, thus needs to set the
> +	 * initial value to 0 themselves in their &drm_fb_helper_funcs->fb_probe
> +	 * callback.
> +	 */
> +	unsigned int open_count;
>  };
>  
>  /**
> @@ -230,6 +246,9 @@ void drm_fb_helper_deferred_io(struct fb_info *info,
>  			       struct list_head *pagelist);
>  int drm_fb_helper_defio_init(struct drm_fb_helper *fb_helper);
>  
> +int drm_fb_helper_fb_open(struct fb_info *info, int user);
> +int drm_fb_helper_fb_release(struct fb_info *info, int user);
> +
>  ssize_t drm_fb_helper_sys_read(struct fb_info *info, char __user *buf,
>  			       size_t count, loff_t *ppos);
>  ssize_t drm_fb_helper_sys_write(struct fb_info *info, const char __user *buf,
> @@ -376,6 +395,16 @@ static inline int drm_fb_helper_defio_init(struct drm_fb_helper *fb_helper)
>  	return -ENODEV;
>  }
>  
> +static inline int drm_fb_helper_fb_open(struct fb_info *info, int user)
> +{
> +	return -ENODEV;
> +}
> +
> +static inline int drm_fb_helper_fb_release(struct fb_info *info, int user)
> +{
> +	return -ENODEV;
> +}
> +
>  static inline ssize_t drm_fb_helper_sys_read(struct fb_info *info,
>  					     char __user *buf, size_t count,
>  					     loff_t *ppos)
> -- 
> 2.15.1
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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