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------------------------------------------在android中，pmem是特地从内存中划出来的一块，给android的用户空间需要物理上连续的进程使用。
我们首先分析pmem驱动。
pmem使用的是platform bus注册的。
1，device部分：
struct platform_device mxc_android_pmem_device = {
.name = "android_pmem",
.id = 0,
};
其data部分：
static struct android_pmem_platform_data android_pmem_pdata = {
.name = "pmem_adsp",
.start = 0,
.size = SZ_32M,
.no_allocator = 0,
.cached = PMEM_NONCACHE_NORMAL,
};
android_pmem_pdata.start在fixup_mxc_board中重新计算了：
size = t->u.mem.size;
android_pmem_pdata.start =
PHYS_OFFSET + size - android_pmem_pdata.size;
2，driver部分：
在drivers/misc/pmem.c定义：
static struct platform_driver pmem_driver = {
.probe = pmem_probe,
.remove = pmem_remove,
.driver = { .name = "android_pmem" }
};
device和driver匹配后将执行pmem_probe：
static int pmem_probe(struct platform_device *pdev)
{
struct android_pmem_platform_data *pdata;
if (!pdev || !pdev->dev.platform_data) {
printk(KERN_ALERT "Unable to probe pmem!\n");
return -1;
}
pdata = pdev->dev.platform_data;
return pmem_setup(pdata, NULL, NULL);//2-1
}
2-1:pmem_setup(pdata, NULL, NULL):
int pmem_setup(struct android_pmem_platform_data *pdata,
long (*ioctl)(struct file *, unsigned int, unsigned long),
int (*release)(struct inode *, struct file *))
{
int err = 0;
int i, index = 0;
int id = id_count;
id_count++;
pmem[id].no_allocator = pdata->no_allocator; //为0
pmem[id].cached = pdata->cached; //PMEM_NONCACHE_NORMAL
pmem[id].buffered = pdata->buffered;
pmem[id].base = pdata->start;//开始位置
pmem[id].size = pdata->size;//大小
pmem[id].ioctl = ioctl;
pmem[id].release = release;
init_rwsem(&pmem[id].bitmap_sem);
init_MUTEX(&pmem[id].data_list_sem);
INIT_LIST_HEAD(&pmem[id].data_list);
pmem[id].dev.name = pdata->name;
pmem[id].dev.minor = id;//次设备好
pmem[id].dev.fops = &pmem_fops;//fops
printk(KERN_INFO "%s: %d init\n", pdata->name, pdata->cached);
err = misc_register(&pmem[id].dev);//注册pmem设备
if (err) {
printk(KERN_ALERT "Unable to register pmem driver!\n");
goto err_cant_register_device;
}
pmem[id].num_entries = pmem[id].size / PMEM_MIN_ALLOC;//有多少页
pmem[id].bitmap = kmalloc(pmem[id].num_entries * //申请这么多个pmem_bits
sizeof(struct pmem_bits), GFP_KERNEL);
if (!pmem[id].bitmap)
goto err_no_mem_for_metadata;
memset(pmem[id].bitmap, 0, sizeof(struct pmem_bits) *
pmem[id].num_entries);
for (i = sizeof(pmem[id].num_entries) * 8 - 1; i >= 0; i--) {
if ((pmem[id].num_entries) & 1<
PMEM_ORDER(id, index) = i;
index = PMEM_NEXT_INDEX(id, index);
}
}
if (pmem[id].cached)
pmem[id].vbase = ioremap_cached(pmem[id].base,
pmem[id].size);
#ifdef ioremap_ext_buffered
else if (pmem[id].buffered)
pmem[id].vbase = ioremap_ext_buffered(pmem[id].base,
pmem[id].size);
#endif
else
pmem[id].vbase = ioremap(pmem[id].base, pmem[id].size);//映射pmem的基地址
if (pmem[id].vbase == 0)
goto error_cant_remap;
pmem[id].garbage_pfn = page_to_pfn(alloc_page(GFP_KERNEL));
if (pmem[id].no_allocator)
pmem[id].allocated = 0;
#if PMEM_DEBUG
debugfs_create_file(pdata->name, S_IFREG | S_IRUGO, NULL, (void *)id,
&debug_fops);
#endif
return 0;
error_cant_remap:
kfree(pmem[id].bitmap);
err_no_mem_for_metadata:
misc_deregister(&pmem[id].dev);
err_cant_register_device:
return -1;
}
我们发现pmem_setup将pmem初始化后注册为misc设备。我们后面上层对pmem访问就是对该misc设备的操作，所以fops非常重要：
struct file_operations pmem_fops = {
.release = pmem_release,
.mmap = pmem_mmap,
.open = pmem_open,
.unlocked_ioctl = pmem_ioctl,
};
我们首先看下pmem_open:
static int pmem_open(struct inode *inode, struct file *file)
{
struct pmem_data *data;//pmem_data结构，每打开一次新建一个pmem_data
int id = get_id(file);
int ret = 0;
DLOG("current %u file %p(%d)\n", current->pid, file, file_count(file));
/* setup file->private_data to indicate its unmapped */
/* you can only open a pmem device one time */
if (file->private_data != NULL)
return -1;
data = kmalloc(sizeof(struct pmem_data), GFP_KERNEL);
if (!data) {
printk("pmem: unable to allocate memory for pmem metadata.");
return -1;
}
data->flags = 0;
data->index = -1;
data->task = NULL;
data->vma = NULL;
data->pid = 0;
data->master_file = NULL;
#if PMEM_DEBUG
data->ref = 0;
#endif
INIT_LIST_HEAD(&data->region_list);
init_rwsem(&data->sem);
file->private_data = data;//赋值
INIT_LIST_HEAD(&data->list);
down(&pmem[id].data_list_sem);
list_add(&data->list, &pmem[id].data_list);//放到data_list
up(&pmem[id].data_list_sem);
return ret;
}
我们看到每打开一个pmem，将有一个pmem_data添加到pmem[id].data_list。并将该pmem_data赋值给file->private_data。
我们在看下pmem_mmap:
static int pmem_mmap(struct file *file, struct vm_area_struct *vma)//这里vma是系统调用时从用户空间找到的一块空闲虚拟空间，用来映射pmem空间
{
struct pmem_data *data;
int index;
unsigned long vma_size = vma->vm_end - vma->vm_start;
int ret = 0, id = get_id(file);
if (vma->vm_pgoff || !PMEM_IS_PAGE_ALIGNED(vma_size)) {
#if PMEM_DEBUG
printk(KERN_ERR "pmem: mmaps must be at offset zero, aligned"
" and a multiple of pages_size.\n");
#endif
return -EINVAL;
}
data = (struct pmem_data *)file->private_data;//打开时保存的pmem_data
down_write(&data->sem);
/* check this file isn't already mmaped, for submaps check this file
* has never been mmaped */
if ((data->flags & PMEM_FLAGS_MASTERMAP) ||
(data->flags & PMEM_FLAGS_SUBMAP) ||
(data->flags & PMEM_FLAGS_UNSUBMAP)) {
#if PMEM_DEBUG
printk(KERN_ERR "pmem: you can only mmap a pmem file once, "
"this file is already mmaped. %x\n", data->flags);
#endif
ret = -EINVAL;
goto error;
}
/* if file->private_data == unalloced, alloc*/
if (data && data->index == -1) {
down_write(&pmem[id].bitmap_sem);
index = pmem_allocate(id, vma->vm_end - vma->vm_start);//从pmem中申请一块内存
up_write(&pmem[id].bitmap_sem);
data->index = index;
}
/* either no space was available or an error occured */
if (!has_allocation(file)) {
ret = -EINVAL;
printk("pmem: could not find allocation for map.\n");
goto error;
}
if (pmem_len(id, data) < vma_size) {
#if PMEM_DEBUG
printk(KERN_WARNING "pmem: mmap size [%lu] does not match"
"size of backing region [%lu].\n", vma_size,
pmem_len(id, data));
#endif
ret = -EINVAL;
goto error;
}
vma->vm_pgoff = pmem_start_addr(id, data) >> PAGE_SHIFT;//pmem的物理地址
vma->vm_page_prot = phys_mem_access_prot(file, vma->vm_page_prot);//映射的标记
if (data->flags & PMEM_FLAGS_CONNECTED) {//该data标记说明是不同进程共享同一块区域
struct pmem_region_node *region_node;
struct list_head *elt;
if (pmem_map_garbage(id, vma, data, 0, vma_size)) {
printk("pmem: mmap failed in kernel!\n");
ret = -EAGAIN;
goto error;
}
list_for_each(elt, &data->region_list) {//从region_list寻找region_node
region_node = list_entry(elt, struct pmem_region_node,
list);
DLOG("remapping file: %p %lx %lx\n", file,
region_node->region.offset,
region_node->region.len);
if (pmem_remap_pfn_range(id, vma, data, //为分配的pmem建立页表
region_node->region.offset,
region_node->region.len)) {
ret = -EAGAIN;
goto error;
}
}
data->flags |= PMEM_FLAGS_SUBMAP;//与其它进程共享
get_task_struct(current->group_leader);
data->task = current->group_leader;
data->vma = vma;
#if PMEM_DEBUG
data->pid = current->pid;
#endif
DLOG("submmapped file %p vma %p pid %u\n", file, vma,
current->pid);
} else {
if (pmem_map_pfn_range(id, vma, data, 0, vma_size)) {////为分配的pmem建立页表
printk(KERN_INFO "pmem: mmap failed in kernel!\n");
ret = -EAGAIN;
goto error;
}
data->flags |= PMEM_FLAGS_MASTERMAP;//第一次映射，即暂时独享
data->pid = current->pid;
}
vma->vm_ops = &vm_ops;
error:
up_write(&data->sem);
return ret;
}
pmem_mmap主要将申请的虚拟用户空间映射到pmem分配的指定空间，利用pmem_map_pfn_range创建页表。
下面看下pmem_ioctl:
static long pmem_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct pmem_data *data;
int id = get_id(file);
switch (cmd) {
case PMEM_GET_PHYS://得到物理参数，如果物理地址，数据长度
{
struct pmem_region region;
DLOG("get_phys\n");
if (!has_allocation(file)) {
region.offset = 0;
region.len = 0;
} else {
data = (struct pmem_data *)file->private_data;
region.offset = pmem_start_addr(id, data);
region.len = pmem_len(id, data);
}
printk(KERN_INFO "pmem: request for physical address of pmem region "
"from process %d.\n", current->pid);
if (copy_to_user((void __user *)arg, ®ion,
sizeof(struct pmem_region)))
return -EFAULT;
break;
}
case PMEM_MAP://映射
{
struct pmem_region region;
if (copy_from_user(®ion, (void __user *)arg,
sizeof(struct pmem_region)))
return -EFAULT;
data = (struct pmem_data *)file->private_data;
return pmem_remap(®ion, file, PMEM_MAP);
}
break;
case PMEM_UNMAP://解映射
{
struct pmem_region region;
if (copy_from_user(®ion, (void __user *)arg,
sizeof(struct pmem_region)))
return -EFAULT;
data = (struct pmem_data *)file->private_data;
return pmem_remap(®ion, file, PMEM_UNMAP);
break;
}
case PMEM_GET_SIZE://得到大小
{
struct pmem_region region;
DLOG("get_size\n");
pmem_get_size(®ion, file);
if (copy_to_user((void __user *)arg, ®ion,
sizeof(struct pmem_region)))
return -EFAULT;
break;
}
case PMEM_GET_TOTAL_SIZE://得到总的pmem大小
{
struct pmem_region region;
DLOG("get total size\n");
region.offset = 0;
get_id(file);
region.len = pmem[id].size;
if (copy_to_user((void __user *)arg, ®ion,
sizeof(struct pmem_region)))
return -EFAULT;
break;
}
case PMEM_ALLOCATE://申请一块pmem内存
{
if (has_allocation(file))
return -EINVAL;
data = (struct pmem_data *)file->private_data;
data->index = pmem_allocate(id, arg);
break;
}
case PMEM_CONNECT://共享pmem内存
DLOG("connect\n");
return pmem_connect(arg, file);
break;
case PMEM_CACHE_FLUSH:
{
struct pmem_region region;
DLOG("flush\n");
if (copy_from_user(®ion, (void __user *)arg,
sizeof(struct pmem_region)))
return -EFAULT;
flush_pmem_file(file, region.offset, region.len);
break;
}
default:
if (pmem[id].ioctl)
return pmem[id].ioctl(file, cmd, arg);
return -EINVAL;
}
return 0;
}
ioctl主要是要搞清楚各个命令的含义。
下面我们看下具体应用，hardware/mx5x/libcamera/Camera_pmem.cpp：
PmemAllocator::PmemAllocator(int bufCount, int bufSize)://构造函数，调用pmem分配时候，将传入两个值分别是 bufCount和bufSize，从变量的名字我们就差不多知道他们意思了。
err_ret(0), mFD(0),mTotalSize(0),mBufCount(bufCount),mBufSize(bufSize),//初始化变量
mVirBase(NULL),mPhyBase(NULL)
{
LOG_FUNCTION_NAME;
memset(mSlotAllocated, 0, sizeof(bool)*MAX_SLOT);//将所有槽的标记清0，它将pmem默认分为MAX_SLOT份，这个分法我认为不是很严谨，容易溢出
int err;
struct pmem_region region;
mFD = open(PMEM_DEV, O_RDWR);//打开pmem设备，就是上面驱动中注册的misc设备
if (mFD < 0) {
LOGE("Error!PmemAllocator constructor");
err_ret = -1;
return;
}
err = ioctl(mFD, PMEM_GET_TOTAL_SIZE, ®ion);//得到总的pmem大小
if (err == 0)
{
LOGE("Info!get pmem total size %d",(int)region.len);
}
else
{
LOGE("Error!Cannot get total length in PmemAllocator constructor");
err_ret = -1;
return;
}
mBufSize = (bufSize + DEFAULT_PMEM_ALIGN-1) & ~(DEFAULT_PMEM_ALIGN-1);//要页对齐的
mTotalSize = mBufSize*bufCount;//要申请的大小
if((mTotalSize > region.len)||(mBufCount > MAX_SLOT)) {//判断pmem是否能满足需求大小
LOGE("Error!Out of PmemAllocator capability");
}
else
{
uint8_t *virtualbase = (uint8_t*)mmap(0, mTotalSize,//映射申请的大小，有上面pmem分析得知，它将会把用户空间映射到pmem区域
PROT_READ|PROT_WRITE, MAP_SHARED, mFD, 0);
if (virtualbase == MAP_FAILED) {
LOGE("Error!mmap(fd=%d, size=%u) failed (%s)",
mFD, (unsigned int)mTotalSize, strerror(errno));
return;
}
memset(®ion, 0, sizeof(region));
if (ioctl(mFD, PMEM_GET_PHYS, ®ion) == -1)//得到映射的物理参数，如物理地址，映射长度
{
LOGE("Error!Failed to get physical address of source!\n");
munmap(virtualbase, mTotalSize);
return;
}
mVirBase = (void *)virtualbase;//赋值给全局变量
mPhyBase = region.offset;//就是刚才得到的物理参数中的
LOGV("Allocator total size %d, vir addr 0x%x, phy addr 0x%x",mTotalSize,mVirBase,mPhyBase);
}
}
PmemAllocator::~PmemAllocator()//析构函数
{
LOG_FUNCTION_NAME;
for(int index=0;index < MAX_SLOT;index ++) {
if(mSlotAllocated[index]) {
LOGE("Error!Cannot deinit PmemAllocator before all memory back to allocator");
}
}
if(mVirBase) {
munmap(mVirBase, mTotalSize);
}
if(mFD) {
close(mFD);
}
}
int PmemAllocator::allocate(struct picbuffer *pbuf, int size)//这个函数的功能是从构造函数中申请的pmem中分配一块bufSize大小的内存
{
LOG_FUNCTION_NAME;
if((!mVirBase)||(!pbuf)||(size>mBufSize)) {//一般size等于mBufSize
LOGE("Error!No memory for allocator");
return -1;
}
for(int index=0;index < MAX_SLOT;index ++) {
if(!mSlotAllocated[index]) {//找到还没被使用的一块
LOGE("Free slot %d for allocating mBufSize %d request size %d",
index,mBufSize,size);
pbuf->virt_start= (unsigned char *)mVirBase+index*mBufSize;
pbuf->phy_offset= mPhyBase+index*mBufSize;
pbuf->length= mBufSize;
mSlotAllocated[index] = true;//置上被使用的标记
return 0;
}
}
return -1;
}
int PmemAllocator::deAllocate(struct picbuffer *pbuf)//删除allocate分配的buffer使用
{
LOG_FUNCTION_NAME;
if((!mVirBase)||(!pbuf)) {
LOGE("Error!No memory for allocator");
return -1;
}
int nSlot = ((unsigned int)pbuf->virt_start- (unsigned int)mVirBase)/mBufSize;
if((nSlot LOGE("Info!deAllocate for slot %d",nSlot);
mSlotAllocated[nSlot] = false;
return 0;
}
else{
LOGE("Error!Not a valid buffer");
return -1;
}
}
uvc camera中使用实例：
#ifdef UVC_CAMERA
{
mPmemAllocator = new PmemAllocator(1, target_size);//实例化PmemAllocator，将调用其构造函数，将向pmem申请1*target_size大小的内存
if(mPmemAllocator->allocate(&(mIPUprocessbuf[0]),target_size) < 0){//申请一块target_size大小的pmem
LOGE("allocate the %d buffer for ipu process error", i);
goto exit1;
}
IPUConverter(mCaptureBuffers[cfilledbuffer.index].phy_offset,mIPUprocessbuf[0].phy_offset,
mPictureWidth,mPictureHeight,mPictureWidth,mPictureHeight,V4L2_PIX_FMT_YUYV,V4L2_PIX_FMT_YUV420);
}
buf1 = mIPUprocessbuf[0].virt_start;
#endif
#ifdef UVC_CAMERA
if (mPmemAllocator != NULL){
mPmemAllocator->deAllocate(&mIPUprocessbuf[0]);//释放刚申请的一块target_size大小的pmem
mPmemAllocator = NULL;
}
if (mCameraOpened != 0)
cameraClose();
#endif
好了，pmem分析基本差不多了。整体分析下来，pmem架构还是比较简单的。它的使用方法依赖上层构建的pmem分配的类，如例子中的话，使用步骤主要有如下步骤：
1，从pmem区申请一片内存
2，使用的时候从申请的一片内存中分配一块，指定其虚拟地址，物理地址和buffersize
3，释放第2步申请的pmem
4，使用结束时，将调用pmem类的析构函数，释放第一步申请的那一片pmem
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