On Tue, Jan 28, 2020 at 3:32 PM Steven A. Falco <[email protected]> wrote: > > On 1/28/20 9:39 AM, Peter Robinson wrote: > > On Tue, Jan 28, 2020 at 1:59 PM Steven A. Falco <[email protected]> > > wrote: > >> > >> I'd like to add an RTC module to a Raspberry Pi. I see that uboot has > >> some support for device tree overlays, but if I'm reading the code > >> correctly, it doesn't seem to be enabled for the Pi. > >> > >> Is it possible to use device tree overlays at this point, or am I better > >> off building a custom kernel? > > > > Yes, mostly, but there's still a whole bunch of corner cases, for > > Raspberry Pi we use the Firmware provided DT and not the kernel DT. > > It's only really clean on aarch64 and completely doesn't work on RPi4 > > (yet another reason there's been no announcement around RPi4 support). > > I see. U-boot says it is using 0:2 /dtb/broadcom/bcm2711-rpi-4-b.dtb, and > I've confirmed that: If I hand-edit that dtb file to add the RTC > (pcf8523@68) to the I2C bus (i2c@7e804000) it works - the RTC is reported as > being managed by the kernel. So it looks like the RPi4 is using the kernel > device tree rather than the firmware one.
Correct, that is the default and on the RPi4 it crashes on boot using the firmware DT. > I have not been entirely successful rebuilding the kernel yet (using mock on > the RPi4 itself). The dtc portion of the build fails because of the gcc10 > change from -fcommon to -fno-common. I need to tweak the kernel spec file to > work around that, but my first attempt was a little too heavy-handed. Seems > that a lot of stuff needs -fno-common, but dtc needs -fcommon. Well patches are welcome, I need to engage with upstream and I only have so many hours in a week. As I've stated previously the RPi4 is currently no supported and we are getting there but I do it in my own personal time. _______________________________________________ arm mailing list -- [email protected] To unsubscribe send an email to [email protected] Fedora Code of Conduct: https://docs.fedoraproject.org/en-US/project/code-of-conduct/ List Guidelines: https://fedoraproject.org/wiki/Mailing_list_guidelines List Archives: https://lists.fedoraproject.org/archives/list/[email protected]
