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

From: Måns Rullgård
Date: Tue Nov 10 2015 - 19:44:33 EST

Andy Shevchenko <andy.shevchenko@xxxxxxxxx> writes:

> 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.

Certainly. I'll re-read memory-barriers.txt to make sure I'm doing the
right thing, then write a better comment.

MÃns RullgÃrd
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