drm: Introduce drm_fb_helper_prepare()

To implement hotplug detection in a race-free manner, drivers must call
drm_kms_helper_poll_init() before hotplug events can be triggered. Such
events can be triggered right after any of the encoders or connectors
are initialized. At the same time, if the drm_fb_helper_hotplug_event()
helper is used by a driver, then the poll helper requires some parts of
the FB helper to be initialized to prevent a crash.

At the same time, drm_fb_helper_init() requires information that is not
necessarily available at such an early stage (number of CRTCs and
connectors), so it cannot be used yet.

Add a new helper, drm_fb_helper_prepare(), that initializes the bare
minimum needed to allow drm_kms_helper_poll_init() to execute and any
subsequent hotplug events to be processed properly.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

1 files changed, 3 insertions, 1 deletions

diff --git a/drivers/gpu/drm/ast/ast_fb.c b/drivers/gpu/drm/ast/ast_fb.c
index 2113894e4ff8..cba45c774552 100644
--- a/drivers/gpu/drm/ast/ast_fb.c
+++ b/drivers/gpu/drm/ast/ast_fb.c
@@ -328,8 +328,10 @@ int ast_fbdev_init(struct drm_device *dev)
                 return -ENOMEM;
 
         ast->fbdev = afbdev;
-        afbdev->helper.funcs = &ast_fb_helper_funcs;
         spin_lock_init(&afbdev->dirty_lock);
+
+        drm_fb_helper_prepare(dev, &afbdev->helper, &ast_fb_helper_funcs);
+
         ret = drm_fb_helper_init(dev, &afbdev->helper,
                                  1, 1);
         if (ret) {