Hi Biju, On Thu, Jun 08, 2023 at 06:41:35AM +0000, Biju Das wrote: > > Subject: RE: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device API > > > Subject: Re: [PATCH v5 01/11] i2c: Enhance i2c_new_ancillary_device > > > API > > > > > > Hi all, > > > > > > sorry for not being able to chime in earlier. > > > > > > > In Biju's particular use case, the i2c device responds to two > > > > addresses, which is the standard i2c ancillary use case. However, > > > > what's special > > > > > > Not quite. ancillary is used when a *driver* needs to take care of two > > > addresses. We already have devices bundling two features into the same > > > chip. I recall at least RTC + EEPROM somewhere. And so far, we have > > > been handling this by creating two nodes in DT and have proper binding docs. > > > I think this is cleaner. First, you can see in DT already what the > > > compound device really consists of. In this case, which RTC and RTC > > > driver is exactly needed. Second, the code added here adds complexity > > > to the I2C core with another layer of inderection for dummy devices. > > > > FYI, please see [1] and [2] > > > > As per DT maintainers, most of PMICs are described with one node, even > > though RTC is on separate address. According to them the DT schema allows > > multiple addresses for children. > > But currently we lacks implementation for that. The enhancement to this > > API allows that. > > > > > > As some resources are shared (knowledge about the clocks), splitting > > > > this in two distinct devices in DT (which is what Biju's initial > > > > patch series did) would need phandles to link both nodes together. > > > > > > > > Do you have a better idea how to represent this? > > > > > > Not sure if I understood this chip correctly, but maybe: The PMIC > > > driver exposes a clock gate which can be consumed by the RTC driver? > > Let me give me some details of this PMIC chip. > > PMIC device has 2 addresses "0x12:- PMIC" , "0x6f"- rtc. > > It has XIN, XOUT, INT# pins and a register for firmware revisions. Is the firmware revision register accessed through address 0x12 (PMIC) or 0x6f (RTC) ? > Based on the system design, > > If XIN and XOUT is connected to external crystal, Internal oscillator > is enabled for RTC. In this case we need to set the oscillator bit to > "0". > > If XIN is connected to external clock source, Internal oscillator is > disabled for RTC. In this case we need to set the oscillator bit to > "1". Same here, which address is the oscillator bit accessed through ? > If XIN and XOUT not connected RTC operation not possible. > > IRQ# (optional) functionality is shared between PMIC and RTC. (PMIC > fault for various bucks/LDOs/WDT/OTP/NVM or alarm condition). IRQs can be shared between multiple devices so this shouldn't be a problem. > The board, I have doesn't populate IRQ# pin. If needed some customers > can populate IRQ# pin and use it for PMIC fault or RTC alarm. > > Also, currently my board has PMIC rev a0 where oscillator bit is > inverted and internal oscillator is enabled (ie: XIN and XOUT is > connected to external crystal) -- Regards, Laurent Pinchart
