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Daniel Vetter authored
Some drivers need to be able to have a perfect race-free fbcon setup. Current drivers only enable hotplug processing after the call to drm_fb_helper_initial_config which leaves a tiny but important race. This race is especially noticable on embedded platforms where the driver itself enables the voltage for the hdmi output, since only then will monitors (after a bit of delay, as usual) respond by asserting the hpd pin. Most of the infrastructure is already there with the split-out drm_fb_helper_init. And drm_fb_helper_initial_config already has all the required locking to handle concurrent hpd events since commit 53f1904b Author: Daniel Vetter <daniel.vetter@ffwll.ch> Date: Thu Mar 20 14:26:35 2014 +0100 drm/fb-helper: improve drm_fb_helper_initial_config locking The only missing bit is making drm_fb_helper_hotplug_event save against concurrent calls of drm_fb_helper_initial_config. The only unprotected bit is the check for fb_helper->fb. With that drivers can first initialize the fb helper, then enabel hotplug processing and then set up the initial config all in a completely race-free manner. Update kerneldoc and convert i915 as a proof of concept. Feature requested by Thierry since his tegra driver atm reliably boots slowly enough to misses the hotplug event for an external hdmi screen, but also reliably boots to quickly for the hpd pin to be asserted when the fb helper calls into the hdmi ->detect function. Cc: Thierry Reding <treding@nvidia.com> Signed-off-by:
Daniel Vetter <daniel.vetter@ffwll.ch> Signed-off-by:
Thierry Reding <treding@nvidia.com> Signed-off-by:
Dave Airlie <airlied@redhat.com>
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