Linux-Doc Archive on lore.kernel.org
 help / color / Atom feed
From: Vladimir Oltean <olteanv@gmail.com>
To: kuba@kernel.org, davem@davemloft.net, netdev@vger.kernel.org
Cc: richardcochran@gmail.com, sorganov@gmail.com, linux-doc@vger.kernel.org
Subject: [PATCH net-next 3/3] docs: networking: timestamping: add a set of frequently asked questions
Date: Fri, 17 Jul 2020 19:10:27 +0300
Message-ID: <20200717161027.1408240-4-olteanv@gmail.com> (raw)
In-Reply-To: <20200717161027.1408240-1-olteanv@gmail.com>

These are some questions I had while trying to explain the behavior of
some drivers with respect to software timestamping. Answered with the
help of Richard Cochran.

Signed-off-by: Vladimir Oltean <olteanv@gmail.com>
---
 Documentation/networking/timestamping.rst | 26 +++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/Documentation/networking/timestamping.rst b/Documentation/networking/timestamping.rst
index 4004c5d2771d..e01ec01179fe 100644
--- a/Documentation/networking/timestamping.rst
+++ b/Documentation/networking/timestamping.rst
@@ -791,3 +791,29 @@ The correct solution to this problem is to implement the PHY timestamping
 requirements in the MAC driver found broken, and submit as a bug fix patch to
 netdev@vger.kernel.org. See :ref:`Documentation/process/stable-kernel-rules.rst
 <stable_kernel_rules>` for more details.
+
+3.4 Frequently asked questions
+------------------------------
+
+Q: When should drivers set SKBTX_IN_PROGRESS?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+When the interface they represent offers both ``SOF_TIMESTAMPING_TX_HARDWARE``
+and ``SOF_TIMESTAMPING_TX_SOFTWARE``.
+Originally, the network stack could deliver either a hardware or a software
+time stamp, but not both. This flag prevents software timestamp delivery.
+This restriction was eventually lifted via the ``SOF_TIMESTAMPING_OPT_TX_SWHW``
+option, but still the original behavior is preserved as the default.
+
+Q: Should drivers that don't offer SOF_TIMESTAMPING_TX_SOFTWARE call skb_tx_timestamp()?
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+The ``skb_clone_tx_timestamp()`` function from its body helps with propagation
+of TX timestamps from PTP PHYs, and the required placement of this call is the
+same as for software TX timestamping.
+Additionally, since PTP is broken on ports with timestamping PHYs and unmet
+requirements, the consequence is that any driver which may be ever coupled to
+a timestamping-capable PHY in ``netdev->phydev`` should call at least
+``skb_clone_tx_timestamp()``. However, calling the higher-level
+``skb_tx_timestamp()`` instead achieves the same purpose, but also offers
+additional compliance to ``SOF_TIMESTAMPING_TX_SOFTWARE``.
-- 
2.25.1


  parent reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17 16:10 [PATCH net-next 0/3] Document more PTP timestamping known quirks Vladimir Oltean
2020-07-17 16:10 ` [PATCH net-next 1/3] docs: networking: timestamping: rename last section to "Known bugs" Vladimir Oltean
2020-07-17 22:05   ` Jacob Keller
2020-07-17 16:10 ` [PATCH net-next 2/3] docs: networking: timestamping: add one more known issue Vladimir Oltean
2020-07-17 23:08   ` Jacob Keller
2020-07-18 11:36     ` Vladimir Oltean
2020-07-17 16:10 ` Vladimir Oltean [this message]
2020-07-17 23:12   ` [PATCH net-next 3/3] docs: networking: timestamping: add a set of frequently asked questions Jacob Keller
2020-07-18 11:35     ` Vladimir Oltean
2020-07-20 18:54       ` Jacob Keller
2020-07-20 21:05         ` Vladimir Oltean
2020-07-20 21:45           ` Jacob Keller
2020-07-20 22:13             ` Vladimir Oltean
2020-07-21  0:21               ` Richard Cochran
2020-07-21 19:51                 ` Vladimir Oltean
2020-07-22  3:25                   ` Richard Cochran
2020-07-25 21:32                     ` Vladimir Oltean
2020-07-21 17:16               ` Jacob Keller
2020-07-21  0:15           ` Richard Cochran
2020-07-17 21:13 ` [PATCH net-next 0/3] Document more PTP timestamping known quirks Sergey Organov
2020-07-17 21:57   ` Vladimir Oltean
2020-07-17 23:13     ` Jacob Keller
2020-07-18 10:54     ` Sergey Organov
2020-07-18 11:30       ` Vladimir Oltean
2020-07-18 13:35         ` Sergey Organov
2020-07-18 11:21 ` Sergey Organov

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20200717161027.1408240-4-olteanv@gmail.com \
    --to=olteanv@gmail.com \
    --cc=davem@davemloft.net \
    --cc=kuba@kernel.org \
    --cc=linux-doc@vger.kernel.org \
    --cc=netdev@vger.kernel.org \
    --cc=richardcochran@gmail.com \
    --cc=sorganov@gmail.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Linux-Doc Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/linux-doc/0 linux-doc/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 linux-doc linux-doc/ https://lore.kernel.org/linux-doc \
		linux-doc@vger.kernel.org
	public-inbox-index linux-doc

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.kernel.vger.linux-doc


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git