netdev - [iwl-net v2 0/2] igc/igb: Fix missing time sync events

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Date: Tue, 20 Feb 2024 15:57:09 -0800
From: Vinicius Costa Gomes <vinicius.gomes@...el.com>
To: intel-wired-lan@...ts.osuosl.org
Cc: sasha.neftin@...el.com,
	richardcochran@...il.com,
	kurt@...utronix.de,
	anthony.l.nguyen@...el.com,
	jesse.brandeburg@...el.com,
	netdev@...r.kernel.org,
	Vinicius Costa Gomes <vinicius.gomes@...el.com>
Subject: [iwl-net v2 0/2] igc/igb: Fix missing time sync events

Hi,

Changes from v1:
 - Reworded cover letter and commit messages, so it's clear that the
   issue is when the same kind of event happens "twice" it might be
   ignored (Richard Cochran);

Link to v1:
https://lore.kernel.org/all/20240217010455.58258-1-vinicius.gomes@intel.com/

It was reported that i225/i226 could sometimes miss some time sync
events when two or more types of events (PPS and Timestamps were used
by the reporter) are being used at the same time under heavy traffic.

The core issue is that the driver was double clearing interrupts, as
the register is both "read to clear" and "write 1 to clear"
(documented in section 8.16.1 of the datasheet), and the handler was
doing both. Which could cause events to be missed if the same kind of
event that triggered the handler happens again between the "read" and
the "write".

Removing the write fixes the issue.

It was tracked down to commit 2c344ae24501 ("igc: Add support for TX
timestamping"), in which I added support for basic timestamp
operations, the issue is that as the hardware operates very similarly
to i210, I used igb code as inspiration. And indeed, the same double
clearing is present there.

But in the igb case, I haven't seen myself or heard about any issues
that seem related to this. So I think it's more like a possible issue.
But it seems like a good idea to fix it there was well.

Vinicius Costa Gomes (2):
  igc: Fix missing time sync events
  igb: Fix missing time sync events

 drivers/net/ethernet/intel/igb/igb_main.c | 23 +++++------------------
 drivers/net/ethernet/intel/igc/igc_main.c | 12 +-----------
 2 files changed, 6 insertions(+), 29 deletions(-)

-- 
2.43.2