使用cma分配内存示例

#include <linux/module.h>
#include <linux/debugfs.h>
#include <linux/miscdevice.h>
#include <linux/dma-mapping.h>
#include <linux/of_device.h>
#include <linux/slab.h>

/*
 *
/ # insmod hd_test.ko
/ # dmesg | grep dma
[ 0.000000] cma: dma_contiguous_reserve(limit 80000000)
[ 0.000000] cma: dma_contiguous_reserve: reserving 16 MiB for global area
[ 126.888985] cl_added:dma_alloc_attrs:254, ops=swiotlb_dma_ops+0x0/0x80
[ 126.945438] cl_added:dma_alloc_from_coherent:163
[ 126.958159] cl_added:dma_alloc_attrs:257, ops=swiotlb_dma_ops+0x0/0x80
[ 126.974582] cl_added:dma_alloc_attrs:263
[ 127.027068] dma_alloc ok, dmabuf=ffff000019601000, addr=7f100000
/ # cat /proc/meminfo | grep -i cma
CmaTotal: 16384 kB
CmaFree: 5888 kB
/ # rmmod hd_test.ko
/ # dmesg | tail -n 5
[ 126.982036] cma: cma_alloc(cma ffff800000b90c90, count 2560, align 8)
[ 127.002513] cma: cma_alloc(): returned ffff7bffc1fc4000
[ 127.027068] dma_alloc ok, dmabuf=ffff000019601000, addr=7f100000
[ 204.600526] cma: cma_release(page ffff7bffc1fc4000)
[ 204.618475] test_module_exit
/ #
/ # cat /proc/meminfo | grep -i cma
CmaTotal: 16384 kB
CmaFree: 15532 kB

 *
/ #


*/

MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("Test module");


static struct miscdevice dummy_test_miscdev = {
    .minor        = MISC_DYNAMIC_MINOR,
    .name        = "dummy_1",
//    .fops        = &dummy_test_fops,
};


static char* dmabuf;
static dma_addr_t addr;
static u64 test_dma_mask = 0x4fffffff;
#define TEST_SIZE 1024*10*1024
static int test_module_init(void)
{
    int rc;

    rc = misc_register(&dummy_test_miscdev);
    if (rc) {
        pr_err("unable to register misc device\n");
    }
    /* configure  dev->archdata.dma_ops = &swiotlb_dma_ops;
     * or this dev's dma_ops is NULL, dma_alloc_coherent will fail */
    of_dma_configure(dummy_test_miscdev.this_device, NULL);
     //arch_setup_dma_ops(dummy_test_miscdev.this_device, 0, 0, NULL,1);
    dummy_test_miscdev.this_device->dma_mask = &test_dma_mask;
    dummy_test_miscdev.this_device->coherent_dma_mask = test_dma_mask;
    dmabuf = dma_alloc_coherent(dummy_test_miscdev.this_device, TEST_SIZE,
                 &addr, GFP_KERNEL);

    if (! dmabuf) {
         pr_err("dma_alloc fail\n");
    } else {
        pr_err("dma_alloc ok, dmabuf=%p, addr=%llx\n", dmabuf, addr);
    }


    return 0;
}

static void test_module_exit(void)
{
    dma_free_coherent(dummy_test_miscdev.this_device, TEST_SIZE, dmabuf, addr);
    misc_deregister(&dummy_test_miscdev);
    pr_err("test_module_exit\n");
    return;
}

module_init(test_module_init);
module_exit(test_module_exit);