Chinese: add translation of io_ordering.txt

This is a Chinese translated version of Documentation/io_ordering.txt

Signed-off-by: Lin Yongting <linyongting@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 67 insertions, 0 deletions

diff --git a/Documentation/zh_CN/io_ordering.txt b/Documentation/zh_CN/io_ordering.txt
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+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  Contact the Chinese maintainer if this translation is outdated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@gmail.com>
+---------------------------------------------------------------------
+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@gmail.com>
+中文版翻译者： 林永听 Lin Yongting <linyongting@gmail.com>
+中文版校译者： 林永听 Lin Yongting <linyongting@gmail.com>
+
+
+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。