Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

From: Andy Shevchenko
Date: Tue Nov 10 2015 - 19:36:48 EST

On Wed, Nov 11, 2015 at 1:07 AM, MÃns RullgÃrd <mans@xxxxxxxxx> wrote:
> Andy Shevchenko <andy.shevchenko@xxxxxxxxx> writes:

>>>>> + nb8800_writel(priv, NB8800_TX_DESC_ADDR, txb->dma_desc);
>>>>> + wmb(); /* ensure desc addr is written before starting DMA */
>>>> Hmâ Have I missed corresponding rmb() ? If it's about MMIO, perhaps mmiowb() ?
>>> Possibly.
>> Standalone wmb() doesn't make sense.
> It does if you need to enforce ordering between normal and I/O memory.
> In fact, since the descriptor is filled in using normal memory accesses,
> my understanding is that mmiowb() would be insufficient here. The
> comment could be improved, however.

Can you then explain what exactly you are assured against in all cases
where you are using wmb()s? It seems I don't recognize this part in
some excerpts.

With Best Regards,
Andy Shevchenko
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