我想要完成的是在PCIe上的FPGA板上的DMA內核中直接訪問的用戶空間中創建一塊內存(不受內核的干擾)。直接訪問用戶空間頁面的物理地址後DMA/Microblaze讀取不正確的數據
爲了做到這一點,我使用posix_memalign()在用戶空間用來在用戶空間分配存儲器(4M)的塊,然後通過一個寫操作通過它的虛擬地址給內核。
在內核中我用下面的代碼來獲取用戶空間內存塊的所有頁面,以創建一個分散/集中列表,並獲得每一頁的所有物理地址:
static ssize_t posix_memory_write(struct file *file, const char __user *buffer, size_t count, loff_t *off)
{
int repeat;
int temporary_point;
int buffer_mapped_pages;
int sg_table_value;
int buffer_dma_buffers = 0;
u32 *u32_posix_buffer = NULL;
int buffer_entries = count/PAGE_SIZE;
struct page **buffer_page_array;
dma_addr_t *dma_address_list_pointer;
int *dma_length_list_pointer;
struct sg_table *dma_sg_table;
struct scatterlist *scatterlist_pointer;
if(posix_buffer != NULL)
{
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] Buffer's Virtual Address is 0x%016lX\n", driver_name, (unsigned long)posix_buffer);
u32_posix_buffer = (u32 *)posix_buffer;
for(repeat = 0; repeat < 16; repeat++)
{
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] Buffer Data: %d\n", driver_name, u32_posix_buffer[repeat]);
}
buffer_page_array = kmalloc(sizeof(struct page *) * buffer_entries, GFP_KERNEL);
down_read(¤t->mm->mmap_sem);
buffer_mapped_pages = get_user_pages(current, current->mm, (unsigned long)(posix_buffer), buffer_entries, 1, 0, buffer_page_array, NULL);
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] Buffer Mapped Pages %d\n", driver_name, buffer_mapped_pages);
for(repeat = 0; repeat < buffer_mapped_pages; repeat++)
{
if (!PageReserved(buffer_page_array[repeat]))
{
SetPageDirty(buffer_page_array[repeat]);
}
page_cache_release(buffer_page_array[repeat]);
}
up_read(¤t->mm->mmap_sem);
dma_sg_table = kmalloc(sizeof(struct sg_table), GFP_KERNEL);
sg_table_value = sg_alloc_table(dma_sg_table, buffer_mapped_pages, GFP_KERNEL);
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] Scatter/Gather Table Return Value %d\n", driver_name, sg_table_value);
scatterlist_pointer = dma_sg_table->sgl;
for(repeat = 0; repeat < buffer_mapped_pages; repeat++)
{
sg_set_page(scatterlist_pointer, buffer_page_array[repeat], PAGE_SIZE, 0);
scatterlist_pointer = sg_next(scatterlist_pointer);
}
scatterlist_pointer = dma_sg_table->sgl;
buffer_dma_buffers = dma_map_sg(&dev->dev, scatterlist_pointer, buffer_mapped_pages, DMA_BIDIRECTIONAL);
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] DMA Buffers are: %d\n", driver_name, buffer_dma_buffers);
dma_address_list_pointer = (dma_addr_t *)kmalloc(sizeof(dma_addr_t) * buffer_dma_buffers, GFP_KERNEL);
dma_length_list_pointer = (int *)kmalloc(sizeof(int) * buffer_dma_buffers, GFP_KERNEL);
for(repeat = 0; repeat < buffer_dma_buffers; repeat++)
{
dma_address_list_pointer[repeat] = sg_dma_address(scatterlist_pointer);
dma_length_list_pointer[repeat] = sg_dma_len(scatterlist_pointer);
scatterlist_pointer = sg_next(scatterlist_pointer);
printk(KERN_ALERT "%s [DEBUG MESSAGE-POSIX MEMORY WRITE] Buffer Page %d DMA Physical Address is: 0x%016lX [SIZE %d Bytes]\n", driver_name, repeat, (unsigned long)dma_address_list_pointer[repeat], dma_length_list_pointer[repeat]);
}
scatterlist_pointer = dma_sg_table->sgl;
//pci_dma_sync_sg_for_device(dev, scatterlist_pointer, buffer_dma_buffers, DMA_TO_DEVICE);
for(repeat = 0; repeat < buffer_mapped_pages; repeat++)
{
writel(dma_address_list_pointer[repeat], (u32 *)bar1_address_virtual + repeat);
}
temporary_point = repeat;
for(repeat = 0; repeat < buffer_mapped_pages; repeat++)
{
writel(dma_length_list_pointer[repeat], (u32 *)bar1_address_virtual + repeat + temporary_point);
}
write_remote_register(bar0_address_virtual, BAR0_OFFSET_GPIO_NOTIFIER + ZERO_OFFSET, (u32) (OPERATION_SET_DMA_ADDRESS_LENGTH_ARRAY_SIZE | buffer_dma_buffers));
}
用4M用戶空間的內存塊我似乎得到了正確的所有物理地址的每個1024頁(頁面大小爲4096字節)。然後我將這些地址寫入FPGA中的BRAM存儲器。
DMA內核和Microblaze處理器都使用這些地址通過PCIe讀取已分配先前內存塊的用戶空間應用程序寫入的數據。
由於某些原因,DMA/Microblaze的讀取操作不正確。
存儲在用戶空間內存塊中的數據是連續遞增的值(11,12,13,14,15,16 ... 234,235等)。
每次我從一個頁面的物理地址讀取,似乎我得到一塊這樣的連續值,使我相信我得到正確的數據。
問題是我得到了我訪問的所有頁面完全相同的連續遞增值。
在我的情況下會出現什麼問題?這可能是緩存一致性問題嗎?
您是否嘗試過使用dma_alloc_coherent()在內核中分配內存?如果可以的話,它可能會讓事情變得更簡單。 – user5071535
對於初學者,您需要固定這些頁面,以免它們被內核移動或換出。你在運行什麼架構? – Chiggs