netdev - Re: [PATCH net-next V3 3/5] net/mlx4_en: Add HW timestamping (TS) support

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Date:	Sun, 28 Apr 2013 09:46:29 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Amir Vadai <amirv@...lanox.com>
Cc:	"David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Eugenia Emantayev <eugenia@...lanox.com>
Subject: Re: [PATCH net-next V3 3/5] net/mlx4_en: Add HW timestamping (TS)
 support

On Sun, Apr 28, 2013 at 09:33:12AM +0300, Amir Vadai wrote:
> On 25/04/2013 22:26, Richard Cochran wrote:
> > On Tue, Apr 23, 2013 at 07:06:49PM +0300, Amir Vadai wrote:
> > 
> >> +u64 mlx4_en_get_cqe_ts(struct mlx4_cqe *cqe)
> >> +{
> >> +	u64 hi, lo;
> >> +	struct mlx4_ts_cqe *ts_cqe = (struct mlx4_ts_cqe *)cqe;
> >> +
> >> +	lo = (u64)be16_to_cpu(ts_cqe->timestamp_lo);
> >> +	hi = ((u64)be32_to_cpu(ts_cqe->timestamp_hi) + !lo) << 16;
> >                                                      ^^^^^
> > That looks a bit strange. Can you explain?
> 
> We need to increment the high order 32bit by one when the low order
> 16bit value is zero, due to HW limitation.

So 'hi' increases by one, when 'lo' goes from 0x0000 to 0x0001?

Thanks,
Richard
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