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

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Message-ID: <20120928111147.GA7474@netboy.at.omicron.at>
Date:	Fri, 28 Sep 2012 13:11:47 +0200
From:	Richard Cochran <richardcochran@...il.com>
To:	Yevgeny Petrilin <yevgenyp@...lanox.com>
Cc:	davem@...emloft.net, netdev@...r.kernel.org, eugenia@...lanox.co.il
Subject: Re: [PATCH 3/3] net/mlx4_en: Add HW timestamping (TS) support

On Fri, Sep 28, 2012 at 12:03:23PM +0200, Yevgeny Petrilin wrote:
> From: Eugenia Emantayev <eugenia@...lanox.co.il>
> 

...

> diff --git a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> index edd9cb8..10fa453 100644
> --- a/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> +++ b/drivers/net/ethernet/mellanox/mlx4/en_netdev.c
> @@ -1517,6 +1517,60 @@ static int mlx4_en_change_mtu(struct net_device *dev, int new_mtu)
>  	return 0;
>  }
>  
> +static int mlx4_en_hwtstamp_ioctl(struct net_device *dev, struct ifreq *ifr)
> +{
> +	struct mlx4_en_priv *priv = netdev_priv(dev);
> +	struct mlx4_en_dev *mdev = priv->mdev;
> +	struct hwtstamp_config config;
> +
> +	if (copy_from_user(&config, ifr->ifr_data, sizeof(config)))
> +		return -EFAULT;
> +
> +	/* reserved for future extensions */
> +	if (config.flags)
> +		return -EINVAL;
> +
> +	/* device doesn't support time stamping */
> +	if (!(mdev->dev->caps.flags2 & MLX4_DEV_CAP_FLAG2_TS_EN))
> +		return -EINVAL;
> +
> +	/* TX HW timestamp */
> +	switch (config.tx_type) {
> +	case HWTSTAMP_TX_OFF:
> +	case HWTSTAMP_TX_ON:
> +		break;
> +	default:
> +		return -ERANGE;
> +	}
> +
> +	/* RX HW timestamp */
> +	switch (config.rx_filter) {
> +	case HWTSTAMP_FILTER_NONE:
> +	case HWTSTAMP_FILTER_ALL:
> +		break;
> +	default:

Instead of rejecting the HWTSTAMP_FILTER_PTP_ codes out of hand, you
should just accept them, and return by promoting rx_filter to
HWTSTAMP_FILTER_ALL.

[ See Documentation/networking/timestamping.txt ]

> +		return -ERANGE;
> +	}
> +
> +	if (mlx4_en_timestamp_config(dev, config.tx_type, config.rx_filter)) {
> +		config.tx_type = HWTSTAMP_TX_OFF;
> +		config.rx_filter = HWTSTAMP_FILTER_NONE;
> +	}
> +
> +	return copy_to_user(ifr->ifr_data, &config,
> +			    sizeof(config)) ? -EFAULT : 0;
> +}

...

> @@ -363,6 +368,9 @@ struct mlx4_en_dev {
>  	u32                     priv_pdn;
>  	spinlock_t              uar_lock;
>  	u8			mac_removed[MLX4_MAX_PORTS + 1];
> +	struct cyclecounter	cycles;
> +	struct timecounter	clock;
> +	struct timecompare	compare;

I am working on a patch to remove the timecompare stuff altogether
(after removing it from blackfin). It is and was a bad idea, I would
hate to see new drivers using it.

I strongly recommend just offering raw hardware time stamps in
nanosecond resolution. Also, why not expose your device as a PTP
Hardware Clock?

Thanks,
Richard
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