>> Just booted mainline... unline linux-imx, it does not try to init cpu1. >> >> However, imx6dl.dtsi from mainline also has both cpu@0 and cpu@1 >> >> So missing piece in linux-imx is elsewhere :( > > It works as you mentioned - and it relies upon the code you tried to > modify. > > The early boot code detects that the boot CPU is not SMP capable, so > through SMP_ON_UP, it "turns off" SMP support by fixing up the code > and making is_smp() return false. > > This prevents smp_init_cpus() being called, which in turn prevents > imx_smp_init_cpus() executing, which prevents the CPU possible mask > including any CPU but the boot CPU. > > As only the boot CPU is possible, this prevents the SMP code trying > to bring any secondary CPUs online.
I'm still trying to understand what is going on, and my printk()s show that this is not entirely true. When smp_init() is entered on mainline om imx6s, cpu_possible_mask and cpu_present_mask both contain two cpus. These get initialized in arm_dt_init_cpu_maps() and stay unmodified since then. But cpu_online() returns 1 for cpu0 and 0 from cpu1 - thus it is cpu_online() check, not possible_mask or present_mask, that prevents cpu1 initialization attempt. Not sure I understand logic behind this. With the current code, resulting cpu_possible_mask depends on CONFIG_SMP_ON_UP: - if it is set, cpu_possible_mask contains (0 1), as initialized in arm_dt_init_cpu_maps() - if it is not set, cpu_possible_mask contains (0), since imx_smp_init_cpus() removes 1 from there. This does not seem to be intended difference. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
