exec: implement .valid.accepts for subpages

    io_mem_write(section->mr, addr, value, len);

}

static bool subpage_accepts(void *opaque, hwaddr addr,

                            unsigned size, bool is_write)

{

    subpage_t *mmio = opaque;

    unsigned int idx = SUBPAGE_IDX(addr);

    MemoryRegionSection *section;

#if defined(DEBUG_SUBPAGE)

    printf("%s: subpage %p %c len %d addr " TARGET_FMT_plx

           " idx %d\n", __func__, mmio,

           is_write ? 'w' : 'r', len, addr, idx);

#endif

    section = &phys_sections[mmio->sub_section[idx]];

    addr += mmio->base;

    addr -= section->offset_within_address_space;

    addr += section->offset_within_region;

    return memory_region_access_valid(section->mr, addr, size, is_write);

}

static const MemoryRegionOps subpage_ops = {

    .read = subpage_read,

    .write = subpage_write,

    .valid.accepts = subpage_accepts,

    .endianness = DEVICE_NATIVE_ENDIAN,

};