linguini1 commented on PR #18861:
URL: https://github.com/apache/nuttx/pull/18861#issuecomment-4472268809
Okay after reading through the examples, it seems the arm64 architecture
makes the assumption that all arm64 chips can have their cores started the same
way (done via `arm64_start_cpu`). I think (?) this assumption is broken for the
RPi4B since Broadcom's proprietary firmware is loaded in at the start and does
some initial setup (like probably spinning everything but CPU0), whereas the
other arm64 devices NuttX supports are under full control of the NuttX kernel.
My solution at the moment is just to add the spintable modification step in
`arm64_start_cpu` like so:
```c
#ifdef CONFIG_ARCH_CHIP_BCM2711
/* According to the bcm2711.dtsi file in the Linux source tree [1], the
* CPUs on the BCM2711 use a spin-table enable method and poll the
* following addresses:
*
* CPU0: 0x000000d8 (BCM_MBOX_CLR06)
* CPU1: 0x000000e0 (BCM_MBOX_CLR08)
* CPU2: 0x000000e8 (BCM_MBOX_CLR10)
* CPU3: 0x000000f0 (BCM_MBOX_CLR12)
*
* Some kernel docs about booting [2] have a handy explanation of how this
* works:
*
* "polling their cpu-release-addr location, which must be contained in the
* reserved region ... when a read of the location pointed to by the
* cpu-release-addr returns a non-zero value, the CPU must jump to this
* value" [2]
*
* In our case, we want these CPUs to load the NuttX kernel defined by
* `_start`. We don't need to worry about CPU0, that one always starts.
* These are 64-bit words (hence skipping every second register).
*
* [1] https://github.com/raspberrypi/linux/blob/rpi-6.12.y/
* arch/arm/boot/dts/broadcom/bcm2711.dtsi
*
* [2] https://www.kernel.org/doc/Documentation/arm64/booting.txt
*/
putreg64((uint64_t)__start, BCM_SPINTBL_CPU(cpu_num));
#endif
```
which should hopefully do all the CPU startup at the right time and it will
use the `__start` that all other arm64 cores use to start up. I will test this
hopefully tomorrow.
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