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The PTP command register contains enable bits for: - Putting the 64-bit PTPCLKVAL register in add/subtract or write mode - Taking timestamps off of the corrected vs free-running clock - Starting/stopping the TTEthernet scheduling - Starting/stopping PPS output - Resetting the switch When a command needs to be issued (e.g. "change the PTPCLKVAL from write mode to add/subtract mode"), one cannot simply write to the command register setting the PTPCLKADD bit to 1, because that would zeroize the other settings. One also cannot do a read-modify-write (that would be too easy for this hardware) because not all bits of the command register are readable over SPI. So this leaves us with the only option of keeping the value of the PTP command register in the driver, and operating on that. Actually there are 2 types of PTP operations now: - Operations that modify the cached PTP command. These operate on ptp_data->cmd as a pointer. - Operations that apply all previously cached PTP settings, but don't otherwise cache what they did themselves. The sja1105_ptp_reset function is such an example. It copies the ptp_data->cmd on stack before modifying and writing it to SPI. This practically means that struct sja1105_ptp_cmd is no longer an implementation detail, since it needs to be stored in full into struct sja1105_ptp_data, and hence in struct sja1105_private. So the (*ptp_cmd) function prototype can change and take struct sja1105_ptp_cmd as second argument now. Signed-off-by: Vladimir Oltean <olteanv@gmail.com> Signed-off-by: David S. Miller <davem@davemloft.net> |
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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.