Re: [RFC v2 net-next 1/2] rtnetlink: Add new RTM_GETSYNCESTATE message to get SyncE status
flat view
From: Jakub Kicinski <kuba@kernel.org>
Date: 2021-08-31 14:18:05
Also in:
intel-wired-lan, linux-kselftest
On Tue, 31 Aug 2021 14:07:32 +0000 Machnikowski, Maciej wrote:
quoted
quoted
I agree that this also is useful for Time card, yet it's also useful here. PTP subsystem should implement a similar logic to this one for DPLL-driven timers which can lock its frequency to external sources.Why would we have two APIs for doing the same thing? IIUC Richard does not want this in the PTP ioctls which is fair, but we need to cater to devices which do not have netdevs.From technical point of view - it can be explained by the fact that the DPLL driving the SyncE logic can be separate from the one driving PTP. Also SyncE is frequency-only oriented and doesn't care about phase and Time of Day that PTP also needs. The GNSS lock on the PTP side will be multi-layered, as the full lock would mean that our PTP clock is not only syntonized, but also has its time and phase set correctly.
Just because GNSS lock addresses more parameters (potentially) doesn't mean the syntonization part shouldn't be addressed by the same API.
A PTP can reuse the "physical" part of this interface later on, but it also needs to solve more SW-specific challenges, like reporting the PTP lock on a SW level. I agree that having such API for PTP subsystem will be very useful, but let's address SyncE in netdev first and build the PTP netlink on top of what we learn here. We can always move the structures defined here to the layer above without affecting any APIs.
It's a reasonable SW design strategy to start simple. Unfortunately, it doesn't apply to stable uAPI design. You're adding a RTNL op, which will have to be supported for ever. If we add anything "later" it will be a strict addition, and will have to be backward compatible. Which I'm not sure how to do when the object we'd operate on would be completely different (clock vs netdev). As I said I can write the boilerplate code for you if you prefer, the code implementing the command and the driver interface will be almost identical. Is there a reason why RTNL is better?