mainlining shenanigans
566b18c8b7
The TX timestamping procedure for SJA1105 is a bit unconventional because the transmit procedure itself is unconventional. Control packets (and therefore PTP as well) are transmitted to a specific port in SJA1105 using "management routes" which must be written over SPI to the switch. These are one-shot rules that match by destination MAC address on traffic coming from the CPU port, and select the precise destination port for that packet. So to transmit a packet from NET_TX softirq context, we actually need to defer to a process context so that we can perform that SPI write before we send the packet. The DSA master dev_queue_xmit() runs in process context, and we poll until the switch confirms it took the TX timestamp, then we annotate the skb clone with that TX timestamp. This is why the sja1105 driver does not need an skb queue for TX timestamping. But the SJA1110 is a bit (not much!) more conventional, and you can request 2-step TX timestamping through the DSA header, as well as give the switch a cookie (timestamp ID) which it will give back to you when it has the timestamp. So now we do need a queue for keeping the skb clones until their TX timestamps become available. The interesting part is that the metadata frames from SJA1105 haven't disappeared completely. On SJA1105 they were used as follow-ups which contained RX timestamps, but on SJA1110 they are actually TX completion packets, which contain a variable (up to 32) array of timestamps. Why an array? Because: - not only is the TX timestamp on the egress port being communicated, but also the RX timestamp on the CPU port. Nice, but we don't care about that, so we ignore it. - because a packet could be multicast to multiple egress ports, each port takes its own timestamp, and the TX completion packet contains the individual timestamps on each port. This is unconventional because switches typically have a timestamping FIFO and raise an interrupt, but this one doesn't. So the tagger needs to detect and parse meta frames, and call into the main switch driver, which pairs the timestamps with the skbs in the TX timestamping queue which are waiting for one. Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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| arch | ||
| block | ||
| certs | ||
| crypto | ||
| Documentation | ||
| drivers | ||
| fs | ||
| include | ||
| init | ||
| ipc | ||
| kernel | ||
| lib | ||
| LICENSES | ||
| mm | ||
| net | ||
| samples | ||
| scripts | ||
| security | ||
| sound | ||
| tools | ||
| usr | ||
| virt | ||
| .clang-format | ||
| .cocciconfig | ||
| .get_maintainer.ignore | ||
| .gitattributes | ||
| .gitignore | ||
| .mailmap | ||
| COPYING | ||
| CREDITS | ||
| Kbuild | ||
| Kconfig | ||
| MAINTAINERS | ||
| Makefile | ||
| 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 Restructured Text 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.