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

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Message-ID: <yw1xmvulpi6r.fsf@unicorn.mansr.com>
Date:	Tue, 10 Nov 2015 23:07:24 +0000
From:	Måns Rullgård <mans@...sr.com>
To:	Andy Shevchenko <andy.shevchenko@...il.com>
Cc:	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>, slash.tmp@...e.fr
Subject: Re: [PATCH v5] net: ethernet: add driver for Aurora VLSI NB8800 Ethernet controller

Andy Shevchenko <andy.shevchenko@...il.com> writes:

> On Wed, Nov 11, 2015 at 12:34 AM, Måns Rullgård <mans@...sr.com> wrote:
>> Andy Shevchenko <andy.shevchenko@...il.com> writes:
>>
>>>> +static inline void nb8800_maskb(struct nb8800_priv *priv, int reg,
>>>> +                               u32 mask, u32 val)
>>>> +{
>>>> +       u32 old = nb8800_readb(priv, reg);
>>>> +       u32 new = (old & ~mask) | val;
>>>
>>> Shoudn't be "… | (val & mask);" ?
>>
>> No, it's meant to replace the bits in mask with the corresponding bits
>> from val.
>
> But you unconditionally use entire val value which might bring bits
> outside of mask.

Very well, I'll apply the mask to both then.

>>>> +       nb8800_writel(priv, NB8800_TX_DESC_ADDR, txb->dma_desc);
>>>> +       wmb();          /* ensure desc addr is written before starting DMA */
>>>
>>> Hm… 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.

-- 
Måns Rullgård
mans@...sr.com
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