Documentation/ptp: add the existing implementations. - #20208
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The page described how to write a lower-half driver but did not say which ones are in the tree. - List the two lower-half drivers that register a PTP clock, the dummy driver and the Ethernet MAC of the STM32, with the option that enables each. - Say that the clock of the STM32 driver is the PTP counter of the MAC, which is also the time base of the timestamps of the received packets, and not CLOCK_REALTIME. - Say that both use the device number 0 by default and so cannot be registered at the same time. Signed-off-by: Daniel P. Carvalho <danieloak@gmail.com> Assisted-by: Claude:claude-sonnet-5
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Summary
The PTP clock driver page (
Documentation/components/drivers/special/ptp.rst) explains how to write a lower-half driver, but it does not say which ones exist in the tree, and the driver of a real Ethernet MAC was added in #20180. This PR adds an "Existing Implementations" section, in the way that other driver pages do (for example the RPTUN driver porting page). It changes documentation only.The section lists the two lower-half drivers that call
ptp_clock_register()inmaster:drivers/timers/ptp_clock_dummy.c, the dummy driver described in the same page, enabled withCONFIG_PTP_CLOCK_DUMMYand registered as/dev/ptp0at start-up.arch/arm/src/common/stm32/stm32_eth_m3m4_v1.c, the Ethernet MAC of the STM32 (the legacy driver), enabled withCONFIG_PTP_CLOCKandCONFIG_STM32_ETH_PTPand registered as/dev/ptpN, where N is the number of the Ethernet interface. It says that the clock is the PTP counter of the MAC, which is also the time base of the hardware timestamps of the received packets, so those are not values ofCLOCK_REALTIME.It also says that both use the device number 0 by default, so they cannot be registered at the same time. That comes from the code: the dummy driver is initialized with device number 0 in
drivers_initialize()and the STM32 driver registers with the number of the interface.Impact
Documentation only, no code change. Only the page
components/drivers/special/ptpchanges.Testing
Built the documentation with Sphinx 6.2.1 and the packages of
Documentation/Pipfile, without-W: the build succeeds, the new section renders and none of the 19 warnings (duplicate C declarations in other pages) is from this file../tools/checkpatch.shpasses.The statements were checked by reading the code: the only two drivers that register a PTP clock were found with a search for
ptp_clock_register()andptp_clock_dummy_initialize()inmaster.