netdev - Re: [PATCH net 04/10] net: mscc: ocelot: deny TX timestamping of non-PTP packets

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Date:   Mon, 11 Oct 2021 23:30:33 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        "David S. Miller" <davem@...emloft.net>, Po Liu <po.liu@....com>
CC:     Florian Fainelli <f.fainelli@...il.com>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Michael Walle <michael@...le.cc>,
        Rui Sousa <rui.sousa@....com>, "Y.b. Lu" <yangbo.lu@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        "UNGLinuxDriver@...rochip.com" <UNGLinuxDriver@...rochip.com>
Subject: Re: [PATCH net 04/10] net: mscc: ocelot: deny TX timestamping of
 non-PTP packets

On Tue, Oct 12, 2021 at 12:26:10AM +0300, Vladimir Oltean wrote:
> It appears that Ocelot switches cannot timestamp non-PTP frames, I
> tested this using the isochron program at:
> https://github.com/vladimiroltean/tsn-scripts
> 
> with the result that the driver increments the ocelot_port->ts_id
> counter as expected, puts it in the REW_OP, but the hardware seems to
> not timestamp these packets at all, since no IRQ is emitted.
> 
> Therefore check whether we are sending PTP frames, and refuse to
> populate REW_OP otherwise.
> 
> Fixes: 4e3b0468e6d7 ("net: mscc: PTP Hardware Clock (PHC) support")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>
> ---
>  drivers/net/ethernet/mscc/ocelot.c | 15 ++++++++-------
>  1 file changed, 8 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/net/ethernet/mscc/ocelot.c b/drivers/net/ethernet/mscc/ocelot.c
> index 190a5900615b..4a667df9b447 100644
> --- a/drivers/net/ethernet/mscc/ocelot.c
> +++ b/drivers/net/ethernet/mscc/ocelot.c
> @@ -618,16 +618,12 @@ u32 ocelot_ptp_rew_op(struct sk_buff *skb)
>  }
>  EXPORT_SYMBOL(ocelot_ptp_rew_op);
>  
> -static bool ocelot_ptp_is_onestep_sync(struct sk_buff *skb)
> +static bool ocelot_ptp_is_onestep_sync(struct sk_buff *skb,
> +				       unsigned int ptp_class)
>  {
>  	struct ptp_header *hdr;
> -	unsigned int ptp_class;
>  	u8 msgtype, twostep;
>  
> -	ptp_class = ptp_classify_raw(skb);
> -	if (ptp_class == PTP_CLASS_NONE)
> -		return false;
> -
>  	hdr = ptp_parse_header(skb, ptp_class);
>  	if (!hdr)
>  		return false;
> @@ -647,11 +643,16 @@ int ocelot_port_txtstamp_request(struct ocelot *ocelot, int port,
>  {
>  	struct ocelot_port *ocelot_port = ocelot->ports[port];
>  	u8 ptp_cmd = ocelot_port->ptp_cmd;
> +	unsigned int ptp_class;
>  	int err;
>  
> +	ptp_class = ptp_classify_raw(skb);
> +	if (ptp_class == PTP_CLASS_NONE)
> +		return -EINVAL;
> +

I am actually introducing an issue here, sorry that I caught it just now.
The ocelot_port_txtstamp_request() function can actually fall through
without doing anything, for example when PTP timestamping is not enabled
(felix_hwtstamp_set was not called, and ocelot_port->ptp_cmd is 0).
We may still carry PTP frames that must be timestamped by somebody else
(a PHY, a downstream DSA switch etc), and ds->ops->port_txtstamp() will
still get called, because skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP is
true, DSA doesn't have the insight on who has PTP timestamping enabled
and who doesn't.

When attached to a downstream DSA switch who is also the one performing
TX timestamping, we are processing an skb here which has SKBTX_HW_TSTAMP
set, yet is DSA-tagged, so the call to ptp_classify_raw() fails to find
the PTP header. So we print that we are "delivering skb without TX timestamp"
(yay us), whereas before this change, we silently did nothing anyway
because ocelot_port->ptp_cmd was zero, so this is slightly annoying.

I will wait for more feedback on the series then repost tomorrow.

>  	/* Store ptp_cmd in OCELOT_SKB_CB(skb)->ptp_cmd */
>  	if (ptp_cmd == IFH_REW_OP_ORIGIN_PTP) {
> -		if (ocelot_ptp_is_onestep_sync(skb)) {
> +		if (ocelot_ptp_is_onestep_sync(skb, ptp_class)) {
>  			OCELOT_SKB_CB(skb)->ptp_cmd = ptp_cmd;
>  			return 0;
>  		}
> -- 
> 2.25.1
>