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

[Daniel Vetter <daniel@ffwll.ch>]

On Mon, Apr 16, 2018 at 06:10:07PM +0200, Noralf Trønnes wrote:
> 
> Den 16.04.2018 10.46, skrev Daniel Vetter:
> > 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.
> 
> I have to keep the existing restore behaviour for those that don't use
> drm_fb_helper_fb_open(). I do this by setting fb_helper->open_count = 1
> in drm_fb_helper_prepare(). I have tried to give a describtion in the
> @open_count docs.

Ah I missed that. I think having the fbops->fb_op == drm_fb_helper_fb_open
check in the restore function itself, plus a big comment explaining what
you're doing, would be clearer. So instead of always checking the
open_count, only check it when this helper is in use.

> Ofc I could have changed all drivers to use drm_fb_helper_fb_open(), but
> I think that time is better spent moving drivers over to generic fbdev
> instead.

Yeah FIXME (plus maybe todo.rst entry, this is perfect starting task
fodder) is totally good enough.
-Daniel

> 
> Noralf.
> 
> > 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
> > > 
> > > _______________________________________________
> > > Intel-gfx mailing list
> > > Intel-gfx@lists.freedesktop.org
> > > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 

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