Re: [RFC v2 4/8] drm/fb-helper: Ensure driver module is pinned in fb_open()

Daniel Vetter
2018-01-09T10:22:28Z

On Wed, Jan 03, 2018 at 11:21:06PM +0100, Noralf Trønnes wrote:
> If struct fb_ops is defined in a library like cma, fb_open() and fbcon
> takes a ref on the library instead of the driver module. Use
> fb_ops.fb_open/fb_release to ensure that the driver module is pinned.
>
> Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
> ---
> drivers/gpu/drm/drm_fb_helper.c | 40 ++++++++++++++++++++++++++++++++++++++++
> include/drm/drm_fb_helper.h | 13 +++++++++++++
> 2 files changed, 53 insertions(+)
>
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index 035784ddd133..2c6adf1d80c2 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -1207,6 +1207,46 @@ void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> }
> EXPORT_SYMBOL(drm_fb_helper_cfb_imageblit);
>
> +/**
> + * drm_fb_helper_fb_open - implementation for &fb_ops.fb_open
> + * @info: fbdev registered by the helper
> + * @user: 1=userspace, 0=fbcon
> + *
> + * 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) {

Actually bikeshed potential here: I'd just unconditionally grab the module
reference, makes the code simpler. Or is there a reason not to?
-Daniel

> + if (!try_module_get(dev->driver->fops->owner))
> + return -ENODEV;
> + }
> +
> + 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
> + *
> + * 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 (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_set_suspend - wrapper around fb_set_suspend
> * @fb_helper: driver-allocated fbdev helper, can be NULL
> diff --git a/include/drm/drm_fb_helper.h b/include/drm/drm_fb_helper.h
> index b069433e7fc1..a593f01ff69e 100644
> --- a/include/drm/drm_fb_helper.h
> +++ b/include/drm/drm_fb_helper.h
> @@ -297,6 +297,9 @@ void drm_fb_helper_cfb_copyarea(struct fb_info *info,
> void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> const struct fb_image *image);
>
> +int drm_fb_helper_fb_open(struct fb_info *info, int user);
> +int drm_fb_helper_fb_release(struct fb_info *info, int user);
> +
> void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper, bool suspend);
> void drm_fb_helper_set_suspend_unlocked(struct drm_fb_helper *fb_helper,
> bool suspend);
> @@ -473,6 +476,16 @@ static inline void drm_fb_helper_cfb_imageblit(struct fb_info *info,
> {
> }
>
> +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 void drm_fb_helper_set_suspend(struct drm_fb_helper *fb_helper,
> bool suspend)
> {
> --
> 2.14.2
>

--
Daniel Vetter
Software Engineer, Intel Corporation