On Fri, Apr 01, 2022 at 04:11:20PM +0200, Allan W. Nielsen wrote:
> On 01.04.2022 14:57, Andrew Lunn wrote:
> > On Fri, Apr 01, 2022 at 01:05:19PM +0200, Horatiu Vultur wrote:
> > > Remove the latencies support both from the PHY driver and from the DT.
> > > The IP already has some default latencies values which can be used to get
> > > decent results. It has the following values(defined in ns):
> > > rx-1000mbit: 429
> > > tx-1000mbit: 201
> > > rx-100mbit: 2346
> > > tx-100mbit: 705
> >
> > So one alternative option here is that ptp4l looks at
> >
> > /sys/class/net/<ifname>/phydev/phy_id
> >
> > to identify the PHY, listens to netlink messages to determine the link
> > speed and then applies the correction itself in user space. That gives
> > you a pretty generic solution, works for any existing PHY and pretty
> > much any existing kernel version. And if you want board specific
> > values you can override them in the ptp4l configuration file.
>
> I think it is good to have both options. If you want PTP4L to compensate
> in user-space, do not call the tunable, if you want to HW to compensate,
> call the tunable (this is useful both for users using ptp4l and other
> ptpimplementations).
>
> If system behaves strange, it is easy to see what delays has been
> applied.
I don't actually think that is true. How wound i know that
> > > rx-1000mbit: 429
> > > tx-1000mbit: 201
> > > rx-100mbit: 2346
> > > tx-100mbit: 705
are the default values? I cannot just look at them and obviously see
they are not the default values. I would need to learn what the
default values are of every PHY in linux which allows the PHY to
perform a correction.
Are you also saying that ptp4l needs to read the values from the
driver, calculate the differ from the defaults, and then apply that
difference to the correction specified in the configuration file it
will apply in userspace?
Does the PTP API enforce mutual exclusion for a device? Can there be
multiple applications running on an interface, some which assume the
hardware is configured to perform corrections and some which will
apply the correction in user space?
Richard?
Andrew
On Fri, Apr 01, 2022 at 04:39:10PM +0200, Andrew Lunn wrote:
> Are you also saying that ptp4l needs to read the values from the
> driver, calculate the differ from the defaults, and then apply that
> difference to the correction specified in the configuration file it
> will apply in userspace?
Personally I wouldn't bother with that. At the end of day, users who
care about sub-microsecond performance will need to calibrate their
particular setup. The output of the calibration will be the system
delay asymmetry correction. That number will be applied in ONE place,
namely the user space PTP stack. Breaking it up into little bits is
just extra work for no benefit.
That is why I'm against any of this driver nonsense. The only purpose
of putting values in to the driver is to unpleasantly surprise the end
users after kernel upgrade.
If this driver defaults + run time query/setting stuff goes mainline,
I'll never use it.
> Does the PTP API enforce mutual exclusion for a device? Can there be
> multiple applications running on an interface, some which assume the
> hardware is configured to perform corrections and some which will
> apply the correction in user space?
There is no mutual exclusion at the kernel API. The main hindrance is
the SIOCSHWTSTAMP ioctl which is at the device level. The setting
applies system wide and is a root caps operation. There is the "Get"
variant that allows co-operation but does not enforce it.
Thanks,
Richard