linux-kernel - Re: [PATCH net-next v17 04/14] net: Change the API of PHY default timestamp to MAC

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Message-ID: <20240925144649.086b9771@kmaincent-XPS-13-7390>
Date: Wed, 25 Sep 2024 14:46:49 +0200
From: Kory Maincent <kory.maincent@...tlin.com>
To: Jacob Keller <jacob.e.keller@...el.com>
Cc: Florian Fainelli <florian.fainelli@...adcom.com>, "Broadcom internal
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Subject: Re: [PATCH net-next v17 04/14] net: Change the API of PHY default
 timestamp to MAC

Hello Jacob,

On Mon, 29 Jul 2024 11:08:01 -0700
Jacob Keller <jacob.e.keller@...el.com> wrote:

Sorry for answering it so late. I was a bit busy.

> >>> --- a/net/core/timestamping.c
> >>> +++ b/net/core/timestamping.c
> >>> @@ -25,7 +25,8 @@ void skb_clone_tx_timestamp(struct sk_buff *skb)
> >>>  	struct sk_buff *clone;
> >>>  	unsigned int type;
> >>>  
> >>> -	if (!skb->sk)
> >>> +	if (!skb->sk || !skb->dev ||
> >>> +	    !phy_is_default_hwtstamp(skb->dev->phydev))    
> >>
> >> I don't follow why this check is added and its not calling something
> >> like "phy_is_current_hwtstamp"? I guess because we don't yet have a way
> >> to select between MAC/PHY at this point in the series? Ok.  
> > 
> > skb_clone_tx_timestamp is only used for PHY timestamping so we should do
> > nothing if the default PTP is the MAC.
> >   
> 
> I guess my misunderstanding is what about the case where user selects
> PHY timestamping with the netlink command? Then it would still need to
> do the skb_clone_tx_timestamp even though its not the default? Or does
> phy_is_default_hwtstamp take that into account? In which case it would
> make more sense to name it phy_is_current_hwtstamp.
> 
> Either way this is mostly bikeshedding and probably just some
> misunderstanding in my reading of the code.

In fact the phy_is_default_hwtstamp() is only needed in case of no netlink
command used. As you can see in patch 8, we call it only if dev->hwtstamp is
null which mean that a netlink command has been sent. 

Regards,
-- 
Köry Maincent, Bootlin
Embedded Linux and kernel engineering
https://bootlin.com