On 2018-03-28 02:14, Linus Torvalds wrote:
On Tue, Mar 27, 2018 at 5:24 PM, Sinan Kaya <okaya@xxxxxxxxxxxxxx>
wrote:
Basically changing it to
dma_buffer->foo = 1; /* WB */
wmb()
writel_relaxed(KICK, DMA_KICK_REGISTER); /* UC */
mmiowb()
Why?
Why not just remove the wmb(), and keep the barrier in the writel()?
Yes, we want to get there indeed. It is because of some arch not
implementing writel properly. Maintainers want to play safe.
That is why I asked if IA64 and other well known archs follow the
strongly ordered rule at this moment like PPC and ARM.
Or should we go and inform every arch about this before yanking wmb()?
Maintainers are afraid of introducing a regression.
The above code makes no sense, and just looks stupid to me. It also
generates pointlessly bad code on x86, so it's bad there too.
Linus
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