linux-kernel - Re: [PATCH net-next 2/4] net: stmmac: use correct barrier between coherent memory and MMIO

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Date:   Fri, 2 Mar 2018 10:20:00 +0100
From:   Pavel Machek <pavel@....cz>
To:     Niklas Cassel <niklas.cassel@...s.com>
Cc:     Giuseppe Cavallaro <peppe.cavallaro@...com>,
        Alexandre Torgue <alexandre.torgue@...com>,
        Jose.Abreu@...opsys.com, Niklas Cassel <niklass@...s.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next 2/4] net: stmmac: use correct barrier between
 coherent memory and MMIO

Hi!

Thanks for doing the detective work!

> 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.

Could you explain this a bit more (and perhaps in code comment)?

Ensuring other writes are done before writing the "GO!" bit should be
enough, no?

(If it is not, do we need heavier barriers in other places, too?)

Best regards,
							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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