layoutx/dma_util.c

#include "dma_util.h"

#include <fcntl.h>
#include <stdio.h>
#include <string.h>
#include <unistd.h>
#include <sys/ioctl.h>
#include <linux/dma-heap.h>

int dma_heap_alloc(const char *heap_name, size_t size, int *fd) {
    /* Try the requested heap first, then fall back to cma then to
     * system-uncached so existing callers (decoder "cma", detector
     * "reserved") keep working. Callers that must have a <4G buffer (output
     * fds and the composer mirror) pass "system-uncached-dma32", whose pages
     * are guaranteed below 4G. The plain system-uncached heap can hand out
     * pages above 4G, which the RGA driver refuses to import. */
    const char *tries[3];
    int n = 0;
    if (heap_name && heap_name[0]) tries[n++] = heap_name;
    if (n == 0 || strcmp(tries[0], "cma") != 0) tries[n++] = "cma";
    if (n == 0 || strcmp(tries[0], "system-uncached") != 0) tries[n++] = "system-uncached";

    for (int t = 0; t < n; t++) {
        char path[64];
        snprintf(path, sizeof(path), "/dev/dma_heap/%s", tries[t]);
        int heap_fd = open(path, O_RDWR | O_CLOEXEC);
        if (heap_fd < 0) continue;
        struct dma_heap_allocation_data data = {
            .len = size,
            .fd_flags = O_RDWR | O_CLOEXEC,
        };
        int ret = ioctl(heap_fd, DMA_HEAP_IOCTL_ALLOC, &data);
        close(heap_fd);
        if (ret < 0) continue;
        *fd = (int)data.fd;
        return 0;
    }
    return -1;
}