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

[David Miller]

From: Niklas Cassel <niklas.cassel@xxxxxxxx>
Date: Wed, 7 Mar 2018 18:21:57 +0100

> Considering this, you can drop/revert:
> 95eb930a40a0 ("net: stmmac: use correct barrier between coherent memory and MMIO")
> or perhaps you want me to send a revert?

You must submit explicit patches to do a revert or any other change.

> After reverting 95eb930a40a0, we will still have a dma_wmb() _after_ the
> last descriptor word write. You just explained that nothing else is needed
> after the last descriptor word write, so I actually think that this last
> barrier is superfluous.

You don't need one after the last descriptor write.

Look, you're only concerned with ordering within the descriptor writes.

So it's only about:

	desc->a = x;

	/* Write to 'a' must be visible to the hardware before 'b'. */
	dma_wmb();
	desc->b = y;

	writel();

That's all that you need.