This is a Chinese translated version of Documentation/io_ordering.txt Signed-off-by: Lin Yongting <linyongting@xxxxxxxxx> --- Documentation/zh_CN/io_ordering.txt | 67 +++++++++++++++++++++++++++++++++++ 1 file changed, 67 insertions(+) create mode 100644 Documentation/zh_CN/io_ordering.txt diff --git a/Documentation/zh_CN/io_ordering.txt b/Documentation/zh_CN/io_ordering.txt new file mode 100644 index 0000000..e592daf --- /dev/null +++ b/Documentation/zh_CN/io_ordering.txt @@ -0,0 +1,67 @@ +Chinese translated version of Documentation/io_orderings.txt + +If you have any comment or update to the content, please contact the +original document maintainer directly. However, if you have a problem +communicating in English you can also ask the Chinese maintainer for +help. Contact the Chinese maintainer if this translation is outdated +or if there is a problem with the translation. + +Chinese maintainer: Lin Yongting <linyongting@xxxxxxxxx> +--------------------------------------------------------------------- +Documentation/io_ordering.txt 的中文翻译 + +如果想评论或更新本文的内容，请直接联系原文档的维护者。如果你使用英文 +交流有困难的话，也可以向中文版维护者求助。如果本翻译更新不及时或者翻 +译存在问题，请联系中文版维护者。 + +中文版维护者： 林永听 Lin Yongting <linyongting@xxxxxxxxx> +中文版翻译者： 林永听 Lin Yongting <linyongting@xxxxxxxxx> +中文版校译者： 林永听 Lin Yongting <linyongting@xxxxxxxxx> + + +以下为正文 +--------------------------------------------------------------------- + +在某些平台上，所谓的内存映射I/O是弱顺序。在这些平台上，驱动开发者有责任 +保证I/O内存映射地址的写操作按程序图意的顺序达到设备。通常读取一个“安全” +设备寄存器或桥寄存器，触发IO芯片清刷未处理的写操作到达设备后才处理读操作， +而达到保证目的。驱动程序通常在spinlock保护的临界区退出之前使用这种技术。 +这也可以保证后面的写操作只在前面的写操作之后到达设备（这非常类似于内存 +屏障操作，mb()，不过仅适用于I/O）。 + +假设一个设备驱动程的具体例子： + + ... +CPU A: spin_lock_irqsave(&dev_lock, flags) +CPU A: val = readl(my_status); +CPU A: ... +CPU A: writel(newval, ring_ptr); +CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... +CPU B: spin_lock_irqsave(&dev_lock, flags) +CPU B: val = readl(my_status); +CPU B: ... +CPU B: writel(newval2, ring_ptr); +CPU B: spin_unlock_irqrestore(&dev_lock, flags) + ... + +上述例子中，设备可能会先接收到newval2的值，然后接收到newval的值，问题就 +发生了。不过很容易通过下面方法来修复： + + ... +CPU A: spin_lock_irqsave(&dev_lock, flags) +CPU A: val = readl(my_status); +CPU A: ... +CPU A: writel(newval, ring_ptr); +CPU A: (void)readl(safe_register); /* 配置寄存器？*/ +CPU A: spin_unlock_irqrestore(&dev_lock, flags) + ... +CPU B: spin_lock_irqsave(&dev_lock, flags) +CPU B: val = readl(my_status); +CPU B: ... +CPU B: writel(newval2, ring_ptr); +CPU B: (void)readl(safe_register); /* 配置寄存器？*/ +CPU B: spin_unlock_irqrestore(&dev_lock, flags) + +在解决方案中，读取safe_register寄存器，触发IO芯片清刷未处理的写操作， +再处理后面的读操作，防止引发数据不一致问题。 -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
