On 13/02/2025 18:52:57+0800, Peng Fan wrote: > On Thu, Feb 13, 2025 at 09:20:32AM +0100, Alexandre Belloni wrote: > >On 13/02/2025 11:30:33+0800, Peng Fan wrote: > >> >> IIUC on any pure DT based system, a device node exists per RTC and hence > >> >> platform device associated with it. And the RTC devices are created with > >> >> parent pointing to unique platform device. > >> >> > >> >> > However i.MX SCMI BBM exports two RTCs(id: 0, id: 1), so to make it work for > >> >> > current RTC framework, we could only pick one RTC and pass the id to BBM > >> >> > server side. > >> >> > > >> >> > I am not sure whether Alexandre wanna me to update the code following each > >> >> > parent could only support one RTC or else. > >> >> > > >> > > >> >I want you to keep your changes local to your driver. I already stated > >> >back in 2018 that you were on your own with the imx-sc driver and that I > >> >don't like seeing multiple abstractions for existing RTCs. What is the > >> >actual use case behind needing to access both RTCs using Linux? > >> >Shouldn't this be handled on your firmware side? > >> > >> The firmware exports two RTCs, RTC0 could be handled by Linux, RTC1 > >> could only be read by Linux and configuable by M7 per current i.MX95 EVK > >> firmware. > > > >This doesn't answer the main question, why is this useful? Where is the > >time of RTC1 coming from and why would linux set a different time on > >RTC0 ? Can't the firwmare just set the same time on both RTC0 and RTC1? > > To current i.MX95 EVK SCMI firmware, RTC0 is SoC internal RTC, RTC1 is > board level RTC which is more acurrate. > > There are safety island in i.MX95, M7 safety core is assigned owner of > RTC1. Linux non-safety is assigned owner of RTC0, but Linux could read RTC1 > time, Linux not able to set alarm of RTC1. > > I need ask firmware developer to see whether RTC1 time could be synced to > RTC0 from firmware level. But considering RTC1 is more accurate, should we > use RTC1? > > The current firmware design is RTC0 is always there and exported, because > it is SoC internal RTC. RTC1 is board level one, it could be optional per > board design and firmware design. > > The firmware could update to only export RTC1 if no safety need it, > but this needs big change to the firmware BBM part, I need check with > firmware developer. But things may not change. > > >What would someone do if RTC0 and RTC1 don't agree on the time? > > RTC1 is more accurate if it is there. > Well, yes, you have your answer here, if the firmware knows RTC1 is more accurate and will be your source of truth, then simply use this one. -- Alexandre Belloni, co-owner and COO, Bootlin Embedded Linux and Kernel engineering https://bootlin.com
