[求助] linux源码中的细节--请教linux大神

描述：linux源码spi.c中有这样的一个函数spi_register_master,其中定义了一个原子量dyn_bus_id（如下面代码的蓝色字体）。 源码如下： int spi_register_master(struct spi_master *master) { static atomic_t dyn_bus_id = ATOMIC_INIT((1<<15) - 1); struct device *dev = master->dev.parent; int status = -ENODEV; int dynamic = 0; if (!dev) return -ENODEV; /* even if it's just one always-selected device, there must * be at least one chipselect */ if (master->num_chipselect == 0) return -EINVAL; /* convention: dynamically assigned bus IDs count down from the max */ if (master->bus_num < 0) { /* FIXME switch to an IDR based scheme, something like * I2C now uses, so we can't run out of "dynamic" IDs */ master->bus_num = atomic_dec_return(&dyn_bus_id); dynamic = 1; } /* register the device, then userspace will see it. * registration fails if the bus ID is in use. */ dev_set_name(&master->dev, "spi%u", master->bus_num); status = device_add(&master->dev); if (status < 0) goto done; dev_dbg(dev, "registered master %s%s\n", dev_name(&master->dev), dynamic ? " (dynamic)" : ""); /* populate children from any spi device tables */ scan_boardinfo(master); status = 0; done: return status; } EXPORT_SYMBOL_GPL(spi_register_master); 问题：为什么要定义原子量，其是防止怎样的情况发生，举个例子？ 说明：1.原子量的作用我是知道的，我想知道的是这里利用原子量想防止什么情况发生，举个例子。 2.源码中这样的注释也不了解 /* FIXME switch to an IDR based scheme, something like * I2C now uses, so we can't run out of "dynamic" IDs */ 谢谢大神救小弟于苦恼！ 本帖最后由 whwshiyuan1984 于 2015-12-7 17:25 编辑