84d35492b1
Inheritance of HAL object is performed by composing a child structure of a
single parent structure located at offset 0 followed by new data members
and function pointers in the child structure.
For example,
struct child {
struct parent common;
int a_data_member;
void (*a_method)(struct child *c, int v);
};
HAL code assumes this layout when accessing child structures given a pointer
to a parent structure such that users write code like the following...
void child_method(struct *parent, int v) {
struct child * c = (struct child*)parent;
// do stuff with c
}
Code above will break if a member is added before "common" in "struct child".
This change adds comments that describe the restriction on the location of
parent HAL objects within a derived HAL object. HAL objects that already
have comments that describe the required location of parent objects are not
modified.
Change-Id: Ibe4300275286ef275b2097534c84f1029d761d87
74 lines
2.2 KiB
C
74 lines
2.2 KiB
C
/*
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* Copyright (C) 2013 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#ifndef _HARDWARE_VIBRATOR_H
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#define _HARDWARE_VIBRATOR_H
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#include <hardware/hardware.h>
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__BEGIN_DECLS
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#define VIBRATOR_API_VERSION HARDWARE_MODULE_API_VERSION(1,0)
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/**
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* The id of this module
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*/
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#define VIBRATOR_HARDWARE_MODULE_ID "vibrator"
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/**
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* The id of the main vibrator device
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*/
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#define VIBRATOR_DEVICE_ID_MAIN "main_vibrator"
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struct vibrator_device;
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typedef struct vibrator_device {
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/**
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* Common methods of the vibrator device. This *must* be the first member of
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* vibrator_device as users of this structure will cast a hw_device_t to
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* vibrator_device pointer in contexts where it's known the hw_device_t references a
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* vibrator_device.
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*/
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struct hw_device_t common;
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/** Turn on vibrator
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*
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* What happens when this function is called while the the timeout of a
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* previous call has not expired is implementation dependent.
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*
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* @param timeout_ms number of milliseconds to vibrate
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*
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* @return 0 in case of success, negative errno code else
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*/
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int (*vibrator_on)(struct vibrator_device* vibradev, unsigned int timeout_ms);
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/** Turn off vibrator
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*
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* It is not guaranteed that the vibrator will be immediately stopped: the
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* behaviour is implementation dependent.
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*
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* @return 0 in case of success, negative errno code else
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*/
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int (*vibrator_off)(struct vibrator_device* vibradev);
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} vibrator_device_t;
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static inline int vibrator_open(const struct hw_module_t* module, vibrator_device_t** device)
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{
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return module->methods->open(module, VIBRATOR_DEVICE_ID_MAIN, (struct hw_device_t**)device);
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}
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__END_DECLS
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#endif // _HARDWARE_VIBRATOR_H
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