Re: [PATCH net-next v7 15/16] net: ethtool: ts: Let the active time stamping layer be selectable

["Köry Maincent" <kory.maincent@bootlin.com>]

On Wed, 22 Nov 2023 16:08:50 +0200
Vladimir Oltean <vladimir.oltean@nxp.com> wrote:

> On Wed, Nov 22, 2023 at 02:44:53PM +0100, Köry Maincent wrote:
> > On Tue, 21 Nov 2023 09:43:54 -0800
> > Jakub Kicinski <kuba@kernel.org> wrote:
> >   
> > > On Tue, 21 Nov 2023 18:31:14 +0100 Köry Maincent wrote:  
> > > > - Expand struct hwtstamp_config with a phc_index member for the
> > > > SIOCG/SHWTSTAMP commands.
> > > >   To keep backward compatibility if phc_index is not set in the
> > > > hwtstamp_config data from userspace use the default hwtstamp (the
> > > > default being selected as done in my patch series).
> > > >   Is this possible, would it breaks things?    
> > > 
> > > I'd skip this bit, and focus on the ETHTOOL_TSINFO. Keep the ioctl as
> > > "legacy" and do all the extensions in ethtool. TSINFO_GET can serve
> > > as GET, to avoid adding 3rd command for the same thing. TSINFO_SET
> > > would be new (as you indicate below).  
> > 
> > You say this patch series should simply add TSINFO_SET command to set the
> > current phc_index?
> > 
> > It won't solve your requirement of having simultaneous hwtimestamp and
> > enabling/disabling them through rx_filter and tx_types.
> > You want to do this in another patch series alongside a new
> > SIOCG/SHWTSTAMP_2 ABI?
> >   
> > > > - In netlink part, send one netlink tsinfo skb for each phc_index.    
> > > 
> > > phc_index and netdev combination. A DO command can only generate one
> > > answer (or rather, it should generate only one answer, there are few
> > > hard rules in netlink). So we need to move that functionality to DUMP.
> > > We can filter the DUMP based on user-provided ifindex and/or phc_index.  
> > 
> > Currently, the dumpit function is assigned to ethnl_default_dumpit. Wouldn't
> > the behavior change of the dumpit callback break the ABI?
> > 
> >   
> > > > Could be done in a later patch series:
> > > > - Expand netlink TSINFO with
> > > > ETHTOOL_A_TSINFO_HWSTAMP_PROVIDER_QUALIFIER. Describing this struct:
> > > > enum ethtool_hwstamp_provider_qualifier {
> > > >  	ETHTOOL_HWSTAMP_PROVIDER_QUALIFIER_PRECISE,
> > > >  	ETHTOOL_HWSTAMP_PROVIDER_QUALIFIER_APPROX,
> > > > }; 
> > > > 
> > > >   Set the desired qualifier through TSINFO_SET or through SIOCSHWTSTAMP
> > > > by expanding again the struct hwtstamp_config.  
> > 
> > Just wondering to have a insight of future support, in the case of several
> > provider qualifier and the SIOCG/SHWTSTAMP_2 layout containing the
> > phc_index. Will we be able to talk to the two providers qualifiers
> > simultaneously or is it not possible. To know if the SIOCG/SHWTSTAMP_2
> > layout would contain the description of the qualifier provider.
> > If I understand well your mail in the thread it will be the case right?

> My understanding of Jakub's email was that he wants to see the functionality
> offered by SIOCGHWTSTAMP and SIOCSHWTSTAMP converted to netlink. I don't
> think that ethtool is the correct netlink family for that, given that
> these aren't ethtool ioctls to begin with. Maybe the new netdev netlink
> family. The conversion in its basic form would offer exactly the same
> functionality. The extended netlink messages would have extra attributes
> to identify the targeted hwtstamp provider. In the lack of those
> attributes, the default hwtstamp provider is targeted. The definition of
> the default hwtstamp provider should be as per your current patch set
> (netdev, with a whitelist for current phylib PHYs).
> 
> The _listing_ of hwtstamp providers is what could be done through ethtool
> netlink, similar but not identical to the way in which you are proposing
> today (you are presenting blanket "layers" which correspond to netdev and
> phylib, rather than individual providers).
> 
> The concept of an "active phc_index" would not explicitly exist in the
> UAPI. Thus I'm not sure what's with this TSINFO_SET being floated around.
> The only thing would exist is a configurable rx_filter and tx_type per
> hwtstamp provider (aka "{phc_index, qualifier}"). User space will have
> to learn to select the hwtstamp provider it wants to configure through
> netlink, and use for its class of traffic.
> 
> This is why I mentioned by ndo_hwtstamp_set() conversion, because
> suddenly it is a prerequisite for any further progress to be done.
> You can't convert SIOCSHWTSTAMP to netlink if there are some driver
> implementations which still use ndo_eth_ioctl(). They need to be
> UAPI-agnostic.
> 
> I'm not sure what's with Richard's mention of the "_2" variants of the
> ioctls. Probably a low-effort suggestion which was a bit out of context.
> His main point, that you cannot extend struct hwtstamp_config as that
> has a fixed binary format, is perfectly valid though. This is why
> netlink is preferable, because if done correctly (meaning not with
> NLA_BINARY attributes), then it is much more extensible because all
> attributes are TLVs. Use NLA_BINARY, and you will run into the exact
> extensibility issues that the ioctl interface has.

I appreciate the clarification, it now makes more sense to me.

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