On 12/06/2024 11:16:02+0200, Csókás Bence wrote: > 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. I won't reintroduce UIE but I'm going to fix the issue you see with the pcf2129. > > 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. I agree with Miroslav that if done, this should be subsystem wise and not just for individual drivers. > > Bence > -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
