linux-kernel - Re: [PATCH v3 06/10] net/macb: clean up ring buffer logic

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Date:	Wed, 31 Oct 2012 10:59:24 +0100
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Håvard Skinnemoen <havard@...nnemoen.net>,
	David Laight <David.Laight@...lab.com>
CC:	<netdev@...r.kernel.org>, <davem@...emloft.net>,
	<bhutchings@...arflare.com>,
	<linux-arm-kernel@...ts.infradead.org>, <plagnioj@...osoft.com>,
	<patrice.vilchez@...el.com>, <linux-kernel@...r.kernel.org>,
	<manabian@...il.com>
Subject: Re: [PATCH v3 06/10] net/macb: clean up ring buffer logic

On 10/30/2012 07:22 PM, Håvard Skinnemoen :
> On Tue, Oct 30, 2012 at 4:12 AM, David Laight <David.Laight@...lab.com> wrote:
>>> Instead of masking head and tail every time we increment them, just let them
>>> wrap through UINT_MAX and mask them when subscripting. Add simple accessor
>>> functions to do the subscripting properly to minimize the chances of messing
>>> this up.
>> ...
>>> +static unsigned int macb_tx_ring_avail(struct macb *bp)
>>> +{
>>> +     return TX_RING_SIZE - (bp->tx_head - bp->tx_tail);
>>> +}
>>
>> That one doesn't look quite right to me.
>> Surely it should be masking with 'TX_RING_SIZE - 1'
> 
> Why is that? head and tail can never be more than TX_RING_SIZE apart,
> so it shouldn't make any difference.

Absolutely.

Best regards,
-- 
Nicolas Ferre
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