Broken DMA vs MMIO ordering

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Hi Alpha Maintainers,

memory-barriers.txt has been updated not to require a wmb() before writel()
since Linus asked all infrastructures to follow Intel paradigm where writes
are ordered and they do not require a barrier between a memory update and
HW observation.

https://www.mail-archive.com/netdev@xxxxxxxxxxxxxxx/msg225806.html

https://lkml.org/lkml/2018/3/27/431

We have been auditing all architectures to see if they follow this requirement
or not. 

Arnd raised the following concern

"
extern inline u32 readl(const volatile void __iomem *addr)
{
        u32 ret = __raw_readl(addr);
        mb();
        return ret;
}
extern inline void writel(u32 b, volatile void __iomem *addr)
{
        __raw_writel(b, addr);
        mb();
}

There is a barrier in writel /after/ the access but not before."

Can somebody familiar with alpha evaluate this?

Sinan

-- 
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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