netdev - Re: [PATCH net-next 3/5] net: dsa: mv88e6xxx: Let taggers specify a can

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Date:   Tue, 28 May 2019 21:49:12 -0700
From:   Richard Cochran <richardcochran@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     f.fainelli@...il.com, vivien.didelot@...il.com, andrew@...n.ch,
        davem@...emloft.net, john.stultz@...aro.org, tglx@...utronix.de,
        sboyd@...nel.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next 3/5] net: dsa: mv88e6xxx: Let taggers specify a
 can_timestamp function

On Wed, May 29, 2019 at 02:56:25AM +0300, Vladimir Oltean wrote:
> The newly introduced function is called on both the RX and TX paths.

NAK on this patch.
 
> The boolean returned by port_txtstamp should only return false if the
> driver tried to timestamp the skb but failed.

So you say.
 
> Currently there is some logic in the mv88e6xxx driver that determines
> whether it should timestamp frames or not.
> 
> This is wasteful, because if the decision is to not timestamp them, then
> DSA will have cloned an skb and freed it immediately afterwards.

No, it isn't wasteful.  Look at the tests in that driver to see why.
 
> Additionally other drivers (sja1105) may have other hardware criteria
> for timestamping frames on RX, and the default conditions for
> timestamping a frame are too restrictive.

I'm sorry, but we won't change the frame just for one device that has
design issues.

Please put device specific workarounds into its driver.

Thanks,
Richard