alloc none-cached memory in uboot.

 

 

1. API

arch\arm\include\asm\system.h

void noncached_init(void);

phys_addr_t noncached_alloc(size_t size, size_t align);

 

 

2. implementation

arch/arm/lib/cache.c

#ifdef CONFIG_SYS_NONCACHED_MEMORY
/*
 * Reserve one MMU section worth of address space below the malloc() area that
 * will be mapped uncached.
 */
static unsigned long noncached_start;
static unsigned long noncached_end;
static unsigned long noncached_next;

void noncached_init(void)
{
    phys_addr_t start, end;
    size_t size;

    /* If this calculation changes, update board_f.c:reserve_noncached() */
    end = ALIGN(mem_malloc_start, MMU_SECTION_SIZE) - MMU_SECTION_SIZE;
    size = ALIGN(CONFIG_SYS_NONCACHED_MEMORY, MMU_SECTION_SIZE);
    start = end - size;

    debug("mapping memory %pa-%pa non-cached\n", &start, &end);

    noncached_start = start;
    noncached_end = end;
    noncached_next = start;

#if !CONFIG_IS_ENABLED(SYS_DCACHE_OFF)
    mmu_set_region_dcache_behaviour(noncached_start, size, DCACHE_OFF);
#endif
}

phys_addr_t noncached_alloc(size_t size, size_t align)
{
    phys_addr_t next = ALIGN(noncached_next, align);

    if (next >= noncached_end || (noncached_end - next) < size)
        return 0;

    debug("allocated %zu bytes of uncached memory @%pa\n", size, &next);
    noncached_next = next + size;

    return next;
}
#endif

init: 

board_init_r -> init_sequence_r -> initr_noncached -> noncached_init

 

 

3. usage

3.1 define CONFIG_SYS_NONCACHED_MEMORY

include/configs/mc40_common.h

#define CONFIG_SYS_NONCACHED_MEMORY (1 << 20)    //1MB noncached memory

 

3.2 alloc noncached memory

for example, in dwc_eth_qos.c: 

static void *eqos_alloc_descs(unsigned int num)
{
#ifdef CONFIG_SYS_NONCACHED_MEMORY
    return (void *)noncached_alloc(EQOS_DESCRIPTORS_SIZE,
                      EQOS_DESCRIPTOR_ALIGN);
#else
    return memalign(EQOS_DESCRIPTOR_ALIGN, EQOS_DESCRIPTORS_SIZE);
#endif
}