Linux 預留記憶體 DMA 使用心得

linux reserved memory 預留記憶體

本文採用的是 上文的 「通過dma api預留記憶體」的方式

通過命令

#cat /proc/iomem

7ff00000-7ff00fff : /dma@7ff00000
7ff00000-7ff00fff : /dma@7ff00000
7ff50000-7ff50fff : /hdlcd@7ff50000
7ff60000-7ff60fff : /hdlcd@7ff60000
7ff80000-7ff80fff : /uart@7ff80000
7ff80000-7ff80fff : /uart@7ff80000
7ff90000-7ff90fff : /i2s@7ff90000
7ffa0000-7ffa0fff : /i2c@7ffa0000
7ffc0000-7ffcffff : /ehci@7ffc0000
7ffd0000-7ffd0fff : /memory-controller@7ffd0000
80000000-dfffffff : system ram
....
..

80000000-dfffffff : system ram

reserved-memory ;}

; sample@0x64000000
;

#cat /proc/iomem

7ff00000-7ff00fff : /dma@7ff00000
7ff00000-7ff00fff : /dma@7ff00000
7ff50000-7ff50fff : /hdlcd@7ff50000
7ff60000-7ff60fff : /hdlcd@7ff60000
7ff80000-7ff80fff : /uart@7ff80000
7ff80000-7ff80fff : /uart@7ff80000
7ff90000-7ff90fff : /i2s@7ff90000
7ffa0000-7ffa0fff : /i2c@7ffa0000
7ffc0000-7ffcffff : /ehci@7ffc0000
7ffd0000-7ffd0fff : /memory-controller@7ffd0000
80000000-bfffffff : system ram

define alloc_size (

0x20000000
)/* initialize reserved memory resources */
int rc=0;
dma_addr_t dma_handle;
void
* vaddr;
rc =
of_reserved_mem_device_init
(dev);if
(rc)
/* allocate memory */
dma_set_coherent_mask
(dev,
0xffffffff);
vaddr =
dma_alloc_coherent
(dev, alloc_size,
&dma_handle, gfp_kernel)
;dev_info
(dev,
"allocated coherent memory, vaddr: 0x%0llx, paddr: 0x%0llx\n"
,(u64)lp->vaddr, lp->paddr)
;

dma_handle 是這一塊記憶體區域的實體地址。

dma_alloc_coherent 介紹

/**

* dma_alloc_coherent - allocate consistent memory for dma
* @dev: valid struct device pointer, or null for isa and eisa-like devices
* @size: required memory size
* @handle: bus-specific dma address
* * allocate some uncached, unbuffered memory for a device for
* performing dma. this function allocates pages, and will
* return the cpu-viewed address, and sets @handle to be the
* device-viewed address.
*/void
*dma_alloc_coherent
(struct device *dev, size_t size, dma_addr_t *dma_handle,
int flag)
;

sample_mmap

(struct file *file,
struct vm_area_struct *vma)

/**

* dma_mmap_coherent - map a coherent dma allocation into user space
* @dev: valid struct device pointer, or null for isa and eisa-like devices
* @cpu_addr: kernel cpu-view address returned from dma_alloc_coherent
* @handle: device-view address returned from dma_alloc_coherent
* @size: size of memory originally requested in dma_alloc_coherent
* * map a coherent dma buffer previously allocated by dma_alloc_coherent
* into user space. the coherent dma buffer must not be freed by the
*/int
dma_mmap_coherent
(struct device *dev,
struct vm_area_struct *vma,
void
*cpu_addr, dma_addr_t handle, size_t size)
;

dma_free_coherent

(dev, alloc_size , vaddr , dma_handle)
;

void

dma_free_coherent
(struct device *dev, size_t size,
void
*cpu_addr,
dma_addr_t dma_handle)
free a region of consistent memory you previously allocated. dev,
size and dma_handle must all be the same as those passed into
dma_alloc_coherent()
. cpu_addr must be the virtual address returned by
the dma_alloc_coherent()
.note that unlike their sibling allocation calls, these routines
may only be called with irqs enabled.

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