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, 2 insertions, 1 deletions

diff --git a/drivers/gpu/drm/i915/intel_fbdev.c b/drivers/gpu/drm/i915/intel_fbdev.c
index c942d13cd5cb..347d16220cd0 100644
--- a/drivers/gpu/drm/i915/intel_fbdev.c
+++ b/drivers/gpu/drm/i915/intel_fbdev.c
@@ -623,7 +623,8 @@ int intel_fbdev_init(struct drm_device *dev)
         if (ifbdev == NULL)
                 return -ENOMEM;
 
-        ifbdev->helper.funcs = &intel_fb_helper_funcs;
+        drm_fb_helper_prepare(dev, &ifbdev->helper, &intel_fb_helper_funcs);
+
         if (!intel_fbdev_init_bios(dev, ifbdev))
                 ifbdev->preferred_bpp = 32;