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mirror of https://github.com/edk2-porting/linux-next.git synced 2025-01-09 14:14:00 +08:00
linux-next/include
Vladimir Oltean b6bd41363a ptp: introduce a phase offset in the periodic output request
Some PHCs like the ocelot/felix switch cannot emit generic periodic
output, but just PPS (pulse per second) signals, which:
- don't start from arbitrary absolute times, but are rather
  phase-aligned to the beginning of [the closest next] second.
- have an optional phase offset relative to that beginning of the
  second.

For those, it was initially established that they should reject any
other absolute time for the PTP_PEROUT_REQUEST than 0.000000000 [1].

But when it actually came to writing an application [2] that makes use
of this functionality, we realized that we can't really deal generically
with PHCs that support absolute start time, and with PHCs that don't,
without an explicit interface. Namely, in an ideal world, PHC drivers
would ensure that the "perout.start" value written to hardware will
result in a functional output. This means that if the PTP time has
become in the past of this PHC's current time, it should be
automatically fast-forwarded by the driver into a close enough future
time that is known to work (note: this is necessary only if the hardware
doesn't do this fast-forward by itself). But we don't really know what
is the status for PHC drivers in use today, so in the general sense,
user space would be risking to have a non-functional periodic output if
it simply asked for a start time of 0.000000000.

So let's introduce a flag for this type of reduced-functionality
hardware, named PTP_PEROUT_PHASE. The start time is just "soon", the
only thing we know for sure about this signal is that its rising edge
events, Rn, occur at:

Rn = perout.phase + n * perout.period

The "phase" in the periodic output structure is simply an alias to the
"start" time, since both cannot logically be specified at the same time.
Therefore, the binary layout of the structure is not affected.

[1]: https://patchwork.ozlabs.org/project/netdev/patch/20200320103726.32559-7-yangbo.lu@nxp.com/
[2]: https://www.mail-archive.com/linuxptp-devel@lists.sourceforge.net/msg04142.html

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
2020-07-19 19:22:56 -07:00
..
acpi Merge branch 'acpica' 2020-06-10 17:27:28 +02:00
asm-generic Merge git://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next 2020-07-13 18:04:05 -07:00
clocksource
crypto crypto: af_alg - fix use-after-free in af_alg_accept() due to bh_lock_sock() 2020-06-18 17:09:54 +10:00
drm drm/edid: Replace zero-length array with flexible-array 2020-06-15 23:08:31 -05:00
dt-bindings - qcom : 2020-06-11 12:42:14 -07:00
keys RxRPC: Replace zero-length array with flexible-array 2020-06-15 23:08:32 -05:00
kunit
kvm
linux icmp: support rfc 4884 2020-07-19 19:20:22 -07:00
math-emu
media media updates for v5.8-rc1 2020-06-13 13:09:38 -07:00
misc
net icmp: support rfc 4884 2020-07-19 19:20:22 -07:00
pcmcia
ras
rdma dynamic_debug: add an option to enable dynamic debug for modules only 2020-06-08 11:05:56 -07:00
scsi SCSI misc on 20200605 2020-06-05 15:11:50 -07:00
soc net: mscc: ocelot: extend watermark encoding function 2020-07-13 17:40:02 -07:00
sound ALSA: compress: fix partial_drain completion state 2020-07-07 11:52:18 +02:00
target scsi: target: Rename target_setup_cmd_from_cdb() to target_cmd_parse_cdb() 2020-06-09 21:57:26 -04:00
trace Merge git://git.kernel.org/pub/scm/linux/kernel/git/netdev/net 2020-06-25 18:27:40 -07:00
uapi ptp: introduce a phase offset in the periodic output request 2020-07-19 19:22:56 -07:00
vdso
video
xen xen: netif.h: add a new extra type for XDP 2020-07-01 15:25:14 -07:00