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Karol Kolacinski 53ce7166cb ice: ensure periodic output start time is in the future 
On E800 series hardware, if the start time for a periodic output signal is
programmed into GLTSYN_TGT_H and GLTSYN_TGT_L registers, the hardware logic
locks up and the periodic output signal never starts. Any future attempt to
reprogram the clock function is futile as the hardware will not reset until
a power on.

The ice_ptp_cfg_perout function has logic to prevent this, as it checks if
the requested start time is in the past. If so, a new start time is
calculated by rounding up.

Since commit d755a7e129 ("ice: Cache perout/extts requests and check
flags"), the rounding is done to the nearest multiple of the clock period,
rather than to a full second. This is more accurate, since it ensures the
signal matches the user request precisely.

Unfortunately, there is a race condition with this rounding logic. If the
current time is close to the multiple of the period, we could calculate a
target time that is extremely soon. It takes time for the software to
program the registers, during which time this requested start time could
become a start time in the past. If that happens, the periodic output
signal will lock up.

For large enough periods, or for the logic prior to the mentioned commit,
this is unlikely. However, with the new logic rounding to the period and
with a small enough period, this becomes inevitable.

For example, attempting to enable a 10MHz signal requires a period of 100
nanoseconds. This means in the *best* case, we have 99 nanoseconds to
program the clock output. This is essentially impossible, and thus such a
small period practically guarantees that the clock output function will
lock up.

To fix this, add some slop to the clock time used to check if the start
time is in the past. Because it is not critical that output signals start
immediately, but it *is* critical that we do not brick the function, 0.5
seconds is selected. This does mean that any requested output will be
delayed by at least 0.5 seconds.

This slop is applied before rounding, so that we always round up to the
nearest multiple of the period that is at least 0.5 seconds in the future,
ensuring a minimum of 0.5 seconds to program the clock output registers.

Finally, to ensure that the hardware registers programming the clock output
complete in a timely manner, add a write flush to the end of
ice_ptp_write_perout. This ensures we don't risk any issue with PCIe
transaction batching.

Strictly speaking, this fixes a race condition all the way back at the
initial implementation of periodic output programming, as it is
theoretically possible to trigger this bug even on the old logic when
always rounding to a full second. However, the window is narrow, and the
code has been refactored heavily since then, making a direct backport not
apply cleanly.

Fixes: d755a7e129 ("ice: Cache perout/extts requests and check flags")
Signed-off-by: Karol Kolacinski <karol.kolacinski@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
2025-03-18 09:38:15 -07:00
arch hyperv-fixes for v6.14-rc7 2025-03-11 12:49:51 -10:00
block block-6.14-20250306 2025-03-07 11:12:33 -10:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
Documentation dt-bindings: can: renesas,rcar-canfd: Fix typo in pattern properties for R-Car V4M 2025-03-14 09:50:36 +01:00
drivers ice: ensure periodic output start time is in the future 2025-03-18 09:38:15 -07:00
fs vfs-6.14-rc7.fixes 2025-03-13 07:53:25 -10:00
include net: mana: Support holes in device list reply msg 2025-03-18 11:32:15 +01:00
init Kbuild updates for v6.14 2025-01-31 12:07:07 -08:00
io_uring io_uring-6.14-20250306 2025-03-07 11:09:33 -10:00
ipc treewide: const qualify ctl_tables where applicable 2025-01-28 13:48:37 +01:00
kernel sched_ext: A fix for v6.14-rc6 2025-03-12 11:52:04 -10:00
lib 33 hotfixes. 24 are cc:stable and the remainder address post-6.13 issues 2025-03-08 14:34:06 -10:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm 33 hotfixes. 24 are cc:stable and the remainder address post-6.13 issues 2025-03-08 14:34:06 -10:00
net ipv6: Set errno after ip_fib_metrics_init() in ip6_route_info_create(). 2025-03-18 12:58:08 +01:00
rust Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
samples Driver core api addition for 6.14-rc3 2025-02-16 12:54:42 -08:00
scripts kbuild: install-extmod-build: Fix build when specifying KBUILD_OUTPUT 2025-03-06 20:32:30 +09:00
security Landlock fix for v6.14-rc5 2025-02-26 11:55:44 -08:00
sound ALSA: hda/realtek: Add support for ASUS Zenbook UM3406KA Laptops using CS35L41 HDA 2025-03-05 19:52:56 +01:00
tools Including fixes from netfilter, bluetooth and wireless. 2025-03-13 07:58:48 -10:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-05 04:06:45 +09:00
virt KVM: remove kvm_arch_post_init_vm 2025-02-04 11:27:45 -05:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-01-10 00:17:25 +01:00
.cocciconfig
.editorconfig .editorconfig: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.get_maintainer.ignore MAINTAINERS: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: use host dylib naming convention to support macOS 2025-01-10 01:01:24 +01:00
.mailmap 33 hotfixes. 24 are cc:stable and the remainder address post-6.13 issues 2025-03-08 14:34:06 -10:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: Move Pavel to kernel.org address 2025-02-07 09:12:33 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Including fixes from netfilter, bluetooth and wireless. 2025-03-13 07:58:48 -10:00
Makefile Linux 6.14-rc6 2025-03-09 13:45:25 -10:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.