netdev - Re: [net-next, v3, 2/2] enetc: support PTP Sync packet one-step timestamping

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Message-ID: <d53dba3a-3241-b424-5f86-2d032a33e06d@gmail.com>
Date:   Mon, 12 Apr 2021 22:00:34 +0300
From:   Claudiu Manoil <claudiu.manoil@...il.com>
To:     Yangbo Lu <yangbo.lu@....com>, netdev@...r.kernel.org
Cc:     "David S . Miller" <davem@...emloft.net>,
        Richard Cochran <richardcochran@...il.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Jakub Kicinski <kuba@...nel.org>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Russell King <linux@...linux.org.uk>
Subject: Re: [net-next, v3, 2/2] enetc: support PTP Sync packet one-step
 timestamping

On 12.04.2021 12:03, Yangbo Lu wrote:
> This patch is to add support for PTP Sync packet one-step timestamping.
> Since ENETC single-step register has to be configured dynamically per
> packet for correctionField offeset and UDP checksum update, current
> one-step timestamping packet has to be sent only when the last one
> completes transmitting on hardware. So, on the TX, this patch handles
> one-step timestamping packet as below:
> 
> - Trasmit packet immediately if no other one in transfer, or queue to
>    skb queue if there is already one in transfer.
>    The test_and_set_bit_lock() is used here to lock and check state.
> - Start a work when complete transfer on hardware, to release the bit
>    lock and to send one skb in skb queue if has.
> 
> And the configuration for one-step timestamping on ENETC before
> transmitting is,
> 
> - Set one-step timestamping flag in extension BD.
> - Write 30 bits current timestamp in tstamp field of extension BD.
> - Update PTP Sync packet originTimestamp field with current timestamp.
> - Configure single-step register for correctionField offeset and UDP
>    checksum update.
> 
> Signed-off-by: Yangbo Lu <yangbo.lu@....com>
> ---
[...]
> +	/* Queue one-step Sync packet if already locked */
> +	if (skb->cb[0] & ENETC_F_TX_ONESTEP_SYNC_TSTAMP) {
> +		if (test_and_set_bit_lock(ENETC_TX_ONESTEP_TSTAMP_IN_PROGRESS,
> +					  &priv->flags)) {
fyi, I had to check with objdump that test_and_set_bit_lock translates 
to a atomic bit set operation on ARM64, it's LDSETA. I'd appreciate any 
pointers on how to look it up in the arm64 arch code.

Reviewed-by: Claudiu Manoil <claudiu.manoil@....com>