From mboxrd@z Thu Jan  1 00:00:00 1970
From: Michael Chan <mchan@broadcom.com>
Subject: Re: [PATCH net-next v3] bnxt_en: New Broadcom ethernet driver.
Date: Mon, 19 Oct 2015 15:07:46 -0700
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	 <20151018222150.427d5311@xeon-e3>
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To: Stephen Hemminger <stephen@networkplumber.org>
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On Sun, 2015-10-18 at 22:21 -0700, Stephen Hemminger wrote: 
> On Sat, 17 Oct 2015 00:21:44 -0400
> Michael Chan <mchan@broadcom.com> wrote:
> 
> > +static inline u32 bnxt_tx_avail(struct bnxt *bp, struct bnxt_tx_ring_info *txr)
> > +{
> > +	/* Tell compiler to fetch tx indices from memory. */
> > +	barrier();
> 
> Actually, you are telling compiler not to reorder. Which may not
> be sufficient on some platforms. 

Only a compiler barrier is needed here to prevent the compiler from
optimizing out the memory access of tx_prod and tx_cons, in case it
thinks that it has those values in some registers.

> 
> 
> > +	return bp->tx_ring_size -
> > +		((txr->tx_prod - txr->tx_cons) & bp->tx_ring_mask);
> > +}