Greetings everyone, Padron for joining in so late o/ On Tue, 8 Feb 2022 at 08:42, Hsin-Yi Wang <hsinyi@xxxxxxxxxxxx> wrote: > > drm_dev_register() sets connector->registration_state to > DRM_CONNECTOR_REGISTERED and dev->registered to true. If > drm_connector_set_panel_orientation() is first called after > drm_dev_register(), it will fail several checks and results in following > warning. > > Add a function to create panel orientation property and set default value > to UNKNOWN, so drivers can call this function to init the property earlier > , and let the panel set the real value later. > The warning illustrates a genuine race condition, where userspace will read the old/invalid property value/state. So this patch masks away the WARNING without addressing the actual issue. Instead can we fix the respective drivers, so that no properties are created after drm_dev_register()? Longer version: As we look into drm_dev_register() it's in charge of creating the dev/sysfs nodes (et al). Note that connectors cannot disappear at runtime. For panel orientation, we are creating an immutable connector properly, meaning that as soon as drm_dev_register() is called we must ensure that the property is available (if applicable) and set to the correct value. For illustration, consider the following scenario: - DRM modules are loaded late - are not built-in and not part of initrd (or there's no initrd) - kernel boots - plymouth/similar user-space component kicks in before the driver/module is loaded - module gets loaded, drm_dev_register() kicks in populating /dev/dri/card0 - plymouth opens the dev node and reads DRM_MODE_PANEL_ORIENTATION_UNKNOWN - module updates the orientation property Thanks Emil
