android - hardware

最新推荐文章于 2024-04-30 11:30:00 发布

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本文介绍了Android硬件抽象层(HAL)的基本结构和工作原理，包括核心数据结构hw_module_t和hw_device_t的定义，以及模块加载流程。还详细解释了像素格式和图像转换等概念。

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hardware.h

/*
 * Copyright (C) 2008 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
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#ifndef ANDROID_INCLUDE_HARDWARE_HARDWARE_H
#define ANDROID_INCLUDE_HARDWARE_HARDWARE_H

#include <stdint.h>
#include <sys/cdefs.h>

#include <cutils/native_handle.h>

__BEGIN_DECLS

/*
 * Value for the hw_module_t.tag field
 */

#define MAKE_TAG_CONSTANT(A,B,C,D) (((A) << 24) | ((B) << 16) | ((C) << 8) | (D))

#define HARDWARE_MODULE_TAG MAKE_TAG_CONSTANT('H', 'W', 'M', 'T')
#define HARDWARE_DEVICE_TAG MAKE_TAG_CONSTANT('H', 'W', 'D', 'T')

struct hw_module_t;
struct hw_module_methods_t;
struct hw_device_t;

/**
 * Every hardware module must have a data structure named HAL_MODULE_INFO_SYM
 * and the fields of this data structure must begin with hw_module_t
 * followed by module specific information.
 */
typedef struct hw_module_t {
    /** tag must be initialized to HARDWARE_MODULE_TAG */
    uint32_t tag;

    /** major version number for the module */
    uint16_t version_major;

    /** minor version number of the module */
    uint16_t version_minor;

    /** Identifier of module */
    const char *id;

    /** Name of this module */
    const char *name;

    /** Author/owner/implementor of the module */
    const char *author;

    /** Modules methods */
    struct hw_module_methods_t* methods;

    /** module's dso */
    void* dso;

    /** padding to 128 bytes, reserved for future use */
    uint32_t reserved[32-7];

} hw_module_t;

typedef struct hw_module_methods_t {
    /** Open a specific device */
    int (*open)(const struct hw_module_t* module, const char* id,
            struct hw_device_t** device);

} hw_module_methods_t;

/**
 * Every device data structure must begin with hw_device_t
 * followed by module specific public methods and attributes.
 */
typedef struct hw_device_t {
    /** tag must be initialized to HARDWARE_DEVICE_TAG */
    uint32_t tag;

    /** version number for hw_device_t */
    uint32_t version;

    /** reference to the module this device belongs to */
    struct hw_module_t* module;

    /** padding reserved for future use */
    uint32_t reserved[12];

    /** Close this device */
    int (*close)(struct hw_device_t* device);

} hw_device_t;

/**
 * Name of the hal_module_info
 */
#define HAL_MODULE_INFO_SYM         HMI

/**
 * Name of the hal_module_info as a string
 */
#define HAL_MODULE_INFO_SYM_AS_STR  "HMI"

/**
 * Get the module info associated with a module by id.
 * @return: 0 == success, <0 == error and *pHmi == NULL
 */
int hw_get_module(const char *id, const struct hw_module_t **module);


/**
 * pixel format definitions
 */

enum {
    HAL_PIXEL_FORMAT_RGBA_8888    = 1,
    HAL_PIXEL_FORMAT_RGBX_8888    = 2,
    HAL_PIXEL_FORMAT_RGB_888      = 3,
    HAL_PIXEL_FORMAT_RGB_565      = 4,
    HAL_PIXEL_FORMAT_BGRA_8888    = 5,
    HAL_PIXEL_FORMAT_RGBA_5551    = 6,
    HAL_PIXEL_FORMAT_RGBA_4444    = 7,
    HAL_PIXEL_FORMAT_YCbCr_422_SP = 0x10,
    HAL_PIXEL_FORMAT_YCrCb_420_SP = 0x11,
    HAL_PIXEL_FORMAT_YCbCr_422_P  = 0x12,
    HAL_PIXEL_FORMAT_YCbCr_420_P  = 0x13,
    HAL_PIXEL_FORMAT_YCbCr_422_I  = 0x14,
    HAL_PIXEL_FORMAT_YCbCr_420_I  = 0x15,
    HAL_PIXEL_FORMAT_CbYCrY_422_I = 0x16,
    HAL_PIXEL_FORMAT_CbYCrY_420_I = 0x17,
    HAL_PIXEL_FORMAT_YCbCr_420_SP_TILED = 0x20,
    HAL_PIXEL_FORMAT_YCbCr_420_SP       = 0x21,
    HAL_PIXEL_FORMAT_YCrCb_420_SP_TILED = 0x22,
    HAL_PIXEL_FORMAT_YCrCb_422_SP       = 0x23,
};


/**
 * Transformation definitions
 */

enum {
    /* flip source image horizontally */
    HAL_TRANSFORM_FLIP_H    = 0x01,
    /* flip source image vertically */
    HAL_TRANSFORM_FLIP_V    = 0x02,
    /* rotate source image 90 degrees */
    HAL_TRANSFORM_ROT_90    = 0x04,
    /* rotate source image 180 degrees */
    HAL_TRANSFORM_ROT_180   = 0x03,
    /* rotate source image 270 degrees */
    HAL_TRANSFORM_ROT_270   = 0x07,
};

__END_DECLS

#endif  /* ANDROID_INCLUDE_HARDWARE_HARDWARE_H */

hareware.c

/*
 * Copyright (C) 2008 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
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#include <hardware/hardware.h>

#include <cutils/properties.h>

#include <dlfcn.h>
#include <string.h>
#include <pthread.h>
#include <errno.h>
#include <limits.h>

#define LOG_TAG "HAL"
#include <utils/Log.h>

/** Base path of the hal modules */
#define HAL_LIBRARY_PATH "/system/lib/hw"

/**
 * There are a set of variant filename for modules. The form of the filename
 * is "<MODULE_ID>.variant.so" so for the led module the Dream variants 
 * of base "ro.product.board", "ro.board.platform" and "ro.arch" would be:
 *
 * led.trout.so
 * led.msm7k.so
 * led.ARMV6.so
 * led.default.so
 */

static const char *variant_keys[] = {
    "ro.hardware",  /* This goes first so that it can pick up a different
                       file on the emulator. */
    "ro.product.board",
    "ro.board.platform",
    "ro.arch"
};

static const int HAL_VARIANT_KEYS_COUNT =
    (sizeof(variant_keys)/sizeof(variant_keys[0]));

/**
 * Load the file defined by the variant and if successful
 * return the dlopen handle and the hmi.
 * @return 0 = success, !0 = failure.
 */
static int load(const char *id,
        const char *path,
        const struct hw_module_t **pHmi)
{
    int status;
    void *handle;
    struct hw_module_t *hmi;

    /*
     * load the symbols resolving undefined symbols before
     * dlopen returns. Since RTLD_GLOBAL is not or'd in with
     * RTLD_NOW the external symbols will not be global
     */
    handle = dlopen(path, RTLD_NOW);
    if (handle == NULL) {
        char const *err_str = dlerror();
        LOGE("load: module=%s\n%s", path, err_str?err_str:"unknown");
        status = -EINVAL;
        goto done;
    }

    /* Get the address of the struct hal_module_info. */
    const char *sym = HAL_MODULE_INFO_SYM_AS_STR;
    hmi = (struct hw_module_t *)dlsym(handle, sym);
    if (hmi == NULL) {
        LOGE("load: couldn't find symbol %s", sym);
        status = -EINVAL;
        goto done;
    }

    /* Check that the id matches */
    if (strcmp(id, hmi->id) != 0) {
        LOGE("load: id=%s != hmi->id=%s", id, hmi->id);
        status = -EINVAL;
        goto done;
    }

    hmi->dso = handle;

    /* success */
    status = 0;

    done:
    if (status != 0) {
        hmi = NULL;
        if (handle != NULL) {
            dlclose(handle);
            handle = NULL;
        }
    } else {
        LOGV("loaded HAL id=%s path=%s hmi=%p handle=%p",
                id, path, *pHmi, handle);
    }

    *pHmi = hmi;

    return status;
}

int hw_get_module(const char *id, const struct hw_module_t **module) 
{
    int status;
    int i;
    const struct hw_module_t *hmi = NULL;
    char prop[PATH_MAX];
    char path[PATH_MAX];

    /*
     * Here we rely on the fact that calling dlopen multiple times on
     * the same .so will simply increment a refcount (and not load
     * a new copy of the library).
     * We also assume that dlopen() is thread-safe.
     */

    /* Loop through the configuration variants looking for a module */
    for (i=0 ; i<HAL_VARIANT_KEYS_COUNT+1 ; i++) {
        if (i < HAL_VARIANT_KEYS_COUNT) {
            if (property_get(variant_keys[i], prop, NULL) == 0) {
                continue;
            }
            snprintf(path, sizeof(path), "%s/%s.%s.so",
                    HAL_LIBRARY_PATH, id, prop);
        } else {
            snprintf(path, sizeof(path), "%s/%s.default.so",
                    HAL_LIBRARY_PATH, id);
        }
        if (access(path, R_OK)) {
            continue;
        }
        /* we found a library matching this id/variant */
        break;
    }

    status = -ENOENT;
    if (i < HAL_VARIANT_KEYS_COUNT+1) {
        /* load the module, if this fails, we're doomed, and we should not try
         * to load a different variant. */
        status = load(id, path, module);
    }

    return status;
}