If a specific timecounter has been chosen via sysctl, and a new timecounter
with higher quality registers (presumably in a module that has just been
loaded), do not undo the user's choice by switchin

If a specific timecounter has been chosen via sysctl, and a new timecounter
with higher quality registers (presumably in a module that has just been
loaded), do not undo the user's choice by switching to the new timecounter.

Document that behavior, and also the fact that there is no way to unregister
a timecounter (and thus no way to unload a module containing one).

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Merge ^/head r286422 through r286684.

Merge from HEAD

Only process the PPS event types currently enabled in pps_params.mode.

This makes the PPS API behave correctly, but isn't ideal -- we still end
up capturing PPS data for non-enabled edges, we just d

Only process the PPS event types currently enabled in pps_params.mode.

This makes the PPS API behave correctly, but isn't ideal -- we still end
up capturing PPS data for non-enabled edges, we just don't process the
data into an event that becomes visible outside of kern_tc. That's because
the event type isn't passed to pps_capture(), so it can't do the filtering.
Any solution for capture filtering is going to require touching every driver.

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RFC 2783 requires a status of ETIMEDOUT, not EWOULDBLOCK, on a timeout.

Merge ^/head r285284 through r285340.

Reimplement the ordering requirements for the timehands updates, and
for timehands consumers, by using fences.

Ensure that the timehands->th_generation reset to zero is visible
before the data updat

Reimplement the ordering requirements for the timehands updates, and
for timehands consumers, by using fences.

Ensure that the timehands->th_generation reset to zero is visible
before the data update is visible [*]. tc_setget() allowed data update
writes to become visible before generation (but not on TSO
architectures).

Remove tc_setgen(), tc_getgen() helpers, use atomics inline [**].

Noted by: alc [*]
Requested by: bde [**]
Reviewed by: alc, bde
Sponsored by: The FreeBSD Foundation
MFC after: 3 weeks

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Catch up with HEAD (r280229-r284686).

Merge ^/head r284188 through r284643.

Merge from head

Tweaks for r284178:

Do not include machine/atomic.h explicitely, the header is already included
by sys/systm.h.

Force inlining of tc_getgen() and tc_setgen(). The functions are used
more than once

Tweaks for r284178:

Do not include machine/atomic.h explicitely, the header is already included
by sys/systm.h.

Force inlining of tc_getgen() and tc_setgen(). The functions are used
more than once, which causes compilers with non-aggressive inlining
policies to generate calls.

Suggested by: bde
Sponsored by: The FreeBSD Foundation
MFC after: 1 week

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Merged ^/head r283871 through r284187.

When updating/accessing the timehands, barriers are needed to ensure
that:
- th_generation update is visible after the parameters update is
visible;
- the read of parameters is not reordered before

When updating/accessing the timehands, barriers are needed to ensure
that:
- th_generation update is visible after the parameters update is
visible;
- the read of parameters is not reordered before initial read of
th_generation.

On UP kernels, compiler barriers are enough. For SMP machines, CPU
barriers must be used too, as was confirmed by submitter by testing on
the Freescale T4240 platform with 24 PowerPC processors.

Submitted by: Sebastian Huber <sebastian.huber@embedded-brains.de>
MFC after: 1 week

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Merge sync of head

Merge from HEAD

MFH: r282315-r282534

Sponsored by: The FreeBSD Foundation

Implement a mechanism for making changes in the kernel<->driver PPS
interface without breaking ABI or API compatibility with existing drivers.

The existing data structures used to communicate betwee

Implement a mechanism for making changes in the kernel<->driver PPS
interface without breaking ABI or API compatibility with existing drivers.

The existing data structures used to communicate between the kernel and
driver portions of PPS processing contain no spare/padding fields and no
flags field or other straightforward mechanism for communicating changes
in the structures or behaviors of the code. This makes it difficult to
MFC new features added to the PPS facility. ABI compatibility is
important; out-of-tree drivers in module form are known to exist. (Note
that the existing api_version field in the pps_params structure must
contain the value mandated by RFC 2783 and any RFCs that come along after.)

These changes introduce a pair of abi-version fields which are filled in
by the driver and the kernel respectively to indicate the interface
version. The driver sets its version field before calling the new
pps_init_abi() function. That lets the kernel know how much of the
pps_state structure is understood by the driver and it can avoid using
newer fields at the end of the structure that it knows about if the driver
is a lower version. The kernel fills in its version field during the init
call, letting the driver know what features and data the kernel supports.

To implement the new version information in a way that is backwards
compatible with code from before these changes, the high bit of the
lightly-used 'kcmode' field is repurposed as a flag bit that indicates the
driver is aware of the abi versioning scheme. Basically if this bit is
clear that indicates a "version 0" driver and if it is set the driver_abi
field indicates the version.

These changes also move the recently-added 'mtx' field of pps_state from
the middle to the end of the structure, and make the kernel code that uses
this field conditional on the driver being abi version 1 or higher. It
changes the only driver currently supplying the mtx field, usb_serial, to
use pps_init_abi().

Reviewed by: hselasky@

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MFH: r278968-r280640

Sponsored by: The FreeBSD Foundation

Merge r278538 through r280226.

Merge ^/head r279995 through r280029.

Merge from head

Use sbuf_printf() for sysctl strings instead of stack buffers and snprintf().

Merging ^/head r279596 through r279758.

Add mutex support to the pps_ioctl() API in the kernel.
Bump kernel version to reflect structure change.

PR: 196897
MFC after: 1 week

Merge from HEAD