RE: [PATCH v5 net-next 0/8] dpll/ice: Add TXC DPLL type and full TX reference clock control for E825

[Nitka, Grzegorz]

> -----Original Message-----
> From: Jakub Kicinski <kuba@xxxxxxxxxx>
> Sent: Tuesday, April 7, 2026 4:23 AM
> To: Nitka, Grzegorz <grzegorz.nitka@xxxxxxxxx>
> Cc: netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; intel-wired-
> lan@xxxxxxxxxxxxxxxx; Oros, Petr <poros@xxxxxxxxxx>;
> richardcochran@xxxxxxxxx; andrew+netdev@xxxxxxx; Kitszel, Przemyslaw
> <przemyslaw.kitszel@xxxxxxxxx>; Nguyen, Anthony L
> <anthony.l.nguyen@xxxxxxxxx>; Prathosh.Satish@xxxxxxxxxxxxx; Vecera,
> Ivan <ivecera@xxxxxxxxxx>; jiri@xxxxxxxxxxx; Kubalewski, Arkadiusz
> <arkadiusz.kubalewski@xxxxxxxxx>; vadim.fedorenko@xxxxxxxxx;
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> davem@xxxxxxxxxxxxx; edumazet@xxxxxxxxxx
> Subject: Re: [PATCH v5 net-next 0/8] dpll/ice: Add TXC DPLL type and full TX
> reference clock control for E825
> 
> On Fri,  3 Apr 2026 01:06:18 +0200 Grzegorz Nitka wrote:
> > This series adds TX reference clock support for E825 devices and exposes
> > TX clock selection and synchronization status via the Linux DPLL
> > subsystem.
> > E825 hardware contains a dedicated Tx clock (TXC) domain that is
> > distinct
> > from PPS and EEC. TX reference clock selection is device‑wide, shared
> > across ports, and mediated by firmware as part of the link bring‑up
> > process. As a result, TX clock selection intent may differ from the
> > effective hardware configuration, and software must verify the outcome
> > after link‑up.
> > To support this, the series introduces TXC support incrementally across
> > the DPLL core and the ice driver:
> >
> > - add a new DPLL type (TXC) to represent transmit clock generators;
> 
> I'm not grasping why this is needed, isn't it part of any EEC system
> that the DPLL can drive the TXC? Is your system going to expose multiple
> DPLLs now for one NIC?
> 

Hello Jakub,
For E825 device, the short answer is yes. We have platform EEC now and
we want to add:
- TXC DPLLs per port, and
- PPS DPLL for TSPLL config purposes (in the near future)

EEC (Ethernet Equipment Clock) type DPLL is designed to control multiple
source signals (internal-NIC or external), where one drives the dpll device,
where multiple outputs are possible, each could drive various components
as well as propagate signal to external devices.
TXC is specific dpll device that associated with single ETH port to control it's source,
there is no need to declare any outputs as the single output is already determined.
Basically, having TXC DPLL indicates per port control over SyncE (or some external)
clock source. 

> > - relax DPLL pin registration rules for firmware‑described shared pins
> >   and extend pin notifications with a source identifier;
> > - allow dynamic state control of SyncE reference pins where hardware
> >   supports it;
> > - add CPI infrastructure for PHY‑side TX clock control on E825C;
> > - introduce a TXC DPLL device and TX reference clock pins (EXT_EREF0 and
> >   SYNCE) in the ice driver;
> > - extend the Restart Auto‑Negotiation command to carry a TX reference
> >   clock index;
> > - implement hardware‑backed TX reference clock switching, post‑link
> > - verification, and TX synchronization reporting.
> >
> > TXCLK pins report TX reference topology only. Actual synchronization
> > success is reported via the TXC DPLL lock status, which is updated after
> > hardware verification: external Tx references report LOCKED, while the
> > internal ENET/TXCO source reports UNLOCKED.
> > This provides reliable TX reference selection and observability on E825
> > devices using standard DPLL interfaces, without conflating user intent
> > with effective hardware behavior.