On 6/12/24 09:50, Miroslav Lichvar wrote:
On Tue, Jun 11, 2024 at 10:06:39PM -0700, Richard Cochran wrote:
On Tue, Jun 11, 2024 at 05:04:57PM +0200, Csókás, Bence wrote:
PCF2127/29/31 is capable of generating an interrupt on every
second (SI) or minute (MI) change. It signals this through
the Minute/Second Flag (MSF) as well, which needs to be cleared.
This is a RFC, and my comment is that a PPS from an RTC is not useful
to the Linux kernel.
I think a TCXO-based RTC can be useful to user space to improve
holdover performance with NTP/PTP.
Exactly.
There already is the RTC_UIE_ON
ioctl to enable interrupts and receive them in user space.
The advantage of the PPS device over the ioctl would be more accurate
timestamping (kernel vs user-space). Should PPS be supported, it would
be nice if it worked generally with all drivers that support RTC_UIE_ON.
As we've discussed in v1, UIE hardware support is being removed from the
RTC subsystem, which I tried to optionally re-introduce. Since there was
no response since then, I assumed that there is no willingness to do
that, so I chose the next best option, the PPS subsystem.
On 5/28/24 19:56, Alexandre Belloni wrote:
> This has been removed from the kernel 13 years ago. What is your use
> case to reintroduce it?
I also agree that multiple RTCs would benefit from this feature.
However, we should only add it to those which *have* hardware support
for a "one second has elapsed" signal. UIE is currently implemented by
setting an alarm to the next second, which didn't work well with the
PCF2129.
Bence
