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The last memory barrier in stmmac_xmit()/stmmac_tso_xmit() is placed between a coherent memory write and a MMIO write: The own bit is written in First Desc (TSO: MSS desc or First Desc). <barrier> The DMA engine is started by a write to the tx desc tail pointer/ enable dma transmission register, i.e. a MMIO write. This barrier cannot be a simple dma_wmb(), since a dma_wmb() is only used to guarantee the ordering, with respect to other writes, to cache coherent DMA memory. To guarantee that the cache coherent memory writes have completed before we attempt to write to the cache incoherent MMIO region, we need to use the more heavyweight barrier wmb(). Signed-off-by: Niklas Cassel <niklas.cassel@axis.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.