On Mon, Oct 31, 2022 at 2:41 PM Paul Cercueil <paul@xxxxxxxxxxxxxxx> wrote: > > Hi Rob, > > Le lun. 31 oct. 2022 à 14:23:41 -0500, Rob Herring <robh@xxxxxxxxxx> a > écrit : > > On Fri, Oct 28, 2022 at 11:55:16PM +0100, Paul Cercueil wrote: > >> The RTC in the JZ4770 is compatible with the JZ4760, but has an > >> extra > >> register that permits to configure the behaviour of the CLK32K pin. > >> The > >> same goes for the RTC in the JZ4780. > >> > >> Therefore, the ingenic,jz4770-rtc and ingenic,jz4780-rtc strings do > >> not > >> fall back anymore to ingenic,jz4760-rtc. The ingenic,jz4780-rtc > >> string > >> now falls back to the ingenic,jz4770-rtc string. > > > > This is a compatibility mess. There is no driver support in v6.1-rc > > for > > ingenic,jz4770-rtc, so a new DT would not work with existing kernels. > > It > > sounds like you need 3 compatibles for 4780. > > Do newer DTs need to work with older kernels? I always assumed the > compatibility was only enforced for the other way around. For a stable platform, yes. Would you want a firmware update carrying the DT to break an existing OS install? Compatibility either way ultimately is up to the platform whether you care or not. I just ask that the commit msg spell that out. In this case, it is easily avoided. Rob
