linux-kernel - Re: [PATCH v2 net-next 01/14] dt-bindings: ptp: add NETC Timer PTP clock

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Message-ID: <20250717090547.f5c46ehp5rzey26b@skbuf>
Date: Thu, 17 Jul 2025 12:05:47 +0300
From: Vladimir Oltean <vladimir.oltean@....com>
To: Wei Fang <wei.fang@....com>
Cc: Krzysztof Kozlowski <krzk@...nel.org>,
	"robh@...nel.org" <robh@...nel.org>,
	"krzk+dt@...nel.org" <krzk+dt@...nel.org>,
	"conor+dt@...nel.org" <conor+dt@...nel.org>,
	"richardcochran@...il.com" <richardcochran@...il.com>,
	Claudiu Manoil <claudiu.manoil@....com>,
	Clark Wang <xiaoning.wang@....com>,
	"andrew+netdev@...n.ch" <andrew+netdev@...n.ch>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"vadim.fedorenko@...ux.dev" <vadim.fedorenko@...ux.dev>,
	Frank Li <frank.li@....com>,
	"shawnguo@...nel.org" <shawnguo@...nel.org>,
	"s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
	"festevam@...il.com" <festevam@...il.com>,
	"F.S. Peng" <fushi.peng@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"imx@...ts.linux.dev" <imx@...ts.linux.dev>,
	"kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: Re: [PATCH v2 net-next 01/14] dt-bindings: ptp: add NETC Timer PTP
 clock

On Thu, Jul 17, 2025 at 11:30:14AM +0300, Wei Fang wrote:
> > On Wed, Jul 16, 2025 at 03:30:58PM +0800, Wei Fang wrote:
> > > +properties:
> > > +  compatible:
> > > +    enum:
> > > +      - pci1131,ee02
> > > +
> > > +  reg:
> > > +    maxItems: 1
> > > +
> > > +  clocks:
> > > +    maxItems: 1
> > > +    description:
> > > +      The reference clock of NETC Timer, if not present, indicates that
> > > +      the system clock of NETC IP is selected as the reference clock.
> > 
> > If not present...
> > 
> > > +
> > > +  clock-names:
> > 
> > ... this also is not present...
> > 
> > > +    description:
> > > +      NETC Timer has three reference clock sources, set TMR_CTRL[CK_SEL]
> > > +      by parsing clock name to select one of them as the reference clock.
> > > +      The "system" means that the system clock of NETC IP is used as the
> > > +      reference clock.
> > > +      The "ccm_timer" means another clock from CCM as the reference clock.
> > > +      The "ext_1588" means the reference clock comes from external IO pins.
> > > +    enum:
> > > +      - system
> > 
> > So what does system mean?
> > 
> 
> "system" is the system clock of the NETC subsystem, we can explicitly specify
> this clock as the PTP reference clock of the Timer in the DT node. Or do not
> add clock properties to the DT node, it implicitly indicates that the reference
> clock of the Timer is the "system" clock.

It's unusual to name the clock after the source rather than after the
destination. When "clock-names" takes any of the above 3 values, it's
still the same single IP clock, just taken from 3 different sources.

I see you need to update TMR_CTRL[CK_SEL] depending on where the IP
clock is sourced from. You use the "clock-names" for that. Whereas the
very similar ptp-qoriq uses a separate "fsl,cksel" property. Was that
not an acceptable solution, do we need a new way of achieving the same
thing?

Also, why are "clocks" and "clock-names" not required properties? The
Linux implementation fails probing if they are absent.