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* Copyright (C) 2016 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <stdbool.h>
#include <sys/cdefs.h>
#include <hardware/hardware.h>
* Implement this HAL to receive callbacks when a virtual reality (VR)
* application is being used. VR applications characteristically have a number
* of special display and performance requirements, including:
* - Low sensor latency - Total end-to-end latency from the IMU, accelerometer,
* and gyro to an application-visible callback must be extremely low (<5ms
* typically). This is required for HIFI sensor support.
* - Low display latency - Total end-to-end latency from the GPU draw calls to
* the actual display update must be as low as possible. This is achieved by
* using SurfaceFlinger in a single-buffered mode, and assuring that draw calls
* are synchronized with the display scanout correctly. This behavior is
* exposed via an EGL extension to applications. See below for the EGL
* extensions needed for this.
* - Low-persistence display - Display persistence settings must be set as low as
* possible while still maintaining a reasonable brightness. For a typical
* display running at 60Hz, pixels should be illuminated for <=3.5ms to be
* considered low-persistence. This avoids ghosting during movements in a VR
* setting, and should be enabled from the lights.h HAL when
* - Consistent performance of the GPU and CPU - When given a mixed GPU/CPU
* workload for a VR application with bursts of work at regular intervals
* several times a frame, the CPU scheduling should ensure that the application
* render thread work is run consistently within 1ms of when scheduled, and
* completed before the end of the draw window. To this end, a single CPU core
* must be reserved for solely for the currently running VR application's render
* thread while in VR mode, and made available in the "top-app" cpuset.
* Likewise, an appropriate CPU, GPU, and bus clockrate must be maintained to
* ensure that the rendering workload finishes within the time allotted to
* render each frame when the POWER_HINT_SUSTAINED_PERFORMANCE flag has been
* set in the power.h HAL while in VR mode when the device is not being
* thermally throttled.
* - Required EGL extensions must be present - Any GPU settings required to allow
* the above capabilities are required, including the EGL extensions:
* EGL_ANDROID_create_native_client_buffer, EGL_ANDROID_front_buffer_auto_refresh,
* EGL_EXT_protected_content, EGL_KHR_mutable_render_buffer,
* EGL_KHR_reusable_sync, and EGL_KHR_wait_sync.
* - Accurate thermal reporting - Accurate thermal temperatures and limits must be
* reported in the thermal.h HAL. Specifically, the current skin temperature
* must accurately be reported for DEVICE_TEMPERATURE_SKIN and the
* vr_throttling_threshold reported for this device must accurately report the
* temperature limit above which the device's thermal governor throttles the
* CPU, GPU, and/or bus clockrates below the minimum necessary for consistent
* performance (see previous bullet point).
* In general, vendors implementing this HAL are expected to use set_vr_mode as a
* hint to enable VR-specific performance tuning needed for any of the above
* requirements, and to turn on any device features optimal for VR display
* modes. The set_vr_mode call may simply do nothing if no optimizations are
* available or necessary to meet the above requirements.
* No methods in this HAL will be called concurrently from the Android framework.
typedef struct vr_module {
* Common methods of the module. This *must* be the first member of
* vr_module as users of this structure may cast a hw_module_t to a
* vr_module pointer in contexts where it's known that the hw_module_t
* references a vr_module.
struct hw_module_t common;
* Convenience method for the HAL implementation to set up any state needed
* at runtime startup. This is called once from the VrManagerService during
* its boot phase. No methods from this HAL will be called before init.
void (*init)(struct vr_module *module);
* Set the VR mode state. Possible states of the enabled parameter are:
* false - VR mode is disabled, turn off all VR-specific settings.
* true - VR mode is enabled, turn on all VR-specific settings.
* This is called whenever the the Android system enters or leaves VR mode.
* This will typically occur when the user switches to or from a VR application
* that is doing stereoscopic rendering.
void (*set_vr_mode)(struct vr_module *module, bool enabled);
/* Reserved for future use. Must be NULL. */
void* reserved[8 - 2];
} vr_module_t;