linguini1 commented on code in PR #18861:
URL: https://github.com/apache/nuttx/pull/18861#discussion_r3214683800
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arch/arm64/src/bcm2711/bcm2711_boot.c:
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@@ -124,7 +132,44 @@ int arm64_get_cpuid(uint64_t mpid)
void arm64_el_init(void)
{
- /* TODO: what goes here? */
+ /* 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
+ */
+
+#ifdef CONFIG_SMP
+
+ for (uint8_t cpu = 0; cpu < CONFIG_SMP_NCPUS; cpu++)
+ {
+ putreg64((uint64_t)_start, BCM_SPINTBL_CPU(cpu));
Review Comment:
@xiaoxiang781216 has Xiaomi ever used a device with spin tables for SMP?
Could you inform me if this is a good approach, or if there is a better
starting location to jump to after CPU0 has initialized memory and subsystems?
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