netdev - Re: [PATCH v1 4/8] net: dsa: hellcreek: Add support for hardware timestamping

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Date:   Mon, 13 Jul 2020 07:01:12 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Kurt Kanzenbach <kurt@...utronix.de>
Cc:     Vladimir Oltean <olteanv@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>, devicetree@...r.kernel.org,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        Kamil Alkhouri <kamil.alkhouri@...offenburg.de>,
        ilias.apalodimas@...aro.org
Subject: Re: [PATCH v1 4/8] net: dsa: hellcreek: Add support for hardware
 timestamping

On Mon, Jul 13, 2020 at 12:57:34PM +0200, Kurt Kanzenbach wrote:
> Hi Vladimir,
> 
> On Mon Jul 13 2020, Vladimir Oltean wrote:
> >> +/* Get a pointer to the PTP header in this skb */
> >> +static u8 *parse_ptp_header(struct sk_buff *skb, unsigned int type)
> >
> > Maybe this and the function from mv88e6xxx could share the same
> > implementation somehow.
> 
> Actually both functions are identical. Should it be moved to the ptp
> core, maybe? Then, all drivers could use that. I guess we should also
> define a PTP offset for the reserved field which is accessed in
> hellcreek_get_reserved_field() just with 16 instead of a proper macro
> constant.

I support re-factoring the code that parses the PTP header.  Last time
I looked, each driver needed slightly different fields, and I didn't
see an easy way to accommodate them all.

> > I would like to get some clarification on whether "SKBTX_IN_PROGRESS"
> > should be set in shtx->tx_flags or not. On one hand, it's asking for
> > trouble, on the other hand, it's kind of required for proper compliance
> > to API pre-SO_TIMESTAMPING...
> 
> Hm. We actually oriented our code on the mv88e6xxx time stamping code base.

Where in mv88e6xxx does the driver set SKBTX_IN_PROGRESS?

I don't think it makes sense for DSA drivers to set this bit, as it
serves no purpose in the DSA context.

Thanks,
Richard