ramips: add hack to detect missing mt7621 cpu cores

Signed-off-by: Felix Fietkau <nbd@nbd.name>

target/linux/ramips/patches-4.4/100-mt7621-core-detect-hack.patch

@@ -0,0 +1,61 @@
+There is a variant of MT7621 which contains only one CPU core instead of 2.
+This is not reflected in the config register, so the kernel detects more
+physical cores, which leads to a hang on SMP bringup.
+Add a hack to detect missing cores.
+
+Signed-off-by: Felix Fietkau <nbd@nbd.name>
+
+--- a/arch/mips/kernel/smp-cps.c
++++ b/arch/mips/kernel/smp-cps.c
+@@ -44,6 +44,11 @@ static unsigned core_vpe_count(unsigned
+ 	return (cfg >> CM_GCR_Cx_CONFIG_PVPE_SHF) + 1;
+ }
+ 
++bool __weak plat_cpu_core_present(int core)
++{
++	return true;
++}
++
+ static void __init cps_smp_setup(void)
+ {
+ 	unsigned int ncores, nvpes, core_vpes;
+@@ -53,6 +58,8 @@ static void __init cps_smp_setup(void)
+ 	ncores = mips_cm_numcores();
+ 	pr_info("VPE topology ");
+ 	for (c = nvpes = 0; c < ncores; c++) {
++		if (!plat_cpu_core_present(c))
++			continue;
+ 		core_vpes = core_vpe_count(c);
+ 		pr_cont("%c%u", c ? ',' : '{', core_vpes);
+ 
+--- a/arch/mips/ralink/mt7621.c
++++ b/arch/mips/ralink/mt7621.c
+@@ -20,6 +20,7 @@
+ #include <asm/mips-cpc.h>
+ #include <asm/mach-ralink/ralink_regs.h>
+ #include <asm/mach-ralink/mt7621.h>
++#include <asm/mips-boards/launch.h>
+ 
+ #include <pinmux.h>
+ 
+@@ -163,6 +164,20 @@ void __init ralink_of_remap(void)
+ 		panic("Failed to remap core resources");
+ }
+ 
++bool plat_cpu_core_present(int core)
++{
++	struct cpulaunch *launch = (struct cpulaunch *)CKSEG0ADDR(CPULAUNCH);
++
++	if (!core)
++		return true;
++	launch += core * 2; /* 2 VPEs per core */
++	if (!(launch->flags & LAUNCH_FREADY))
++		return false;
++	if (launch->flags & (LAUNCH_FGO | LAUNCH_FGONE))
++		return false;
++	return true;
++}
++
+ void prom_soc_init(struct ralink_soc_info *soc_info)
+ {
+ 	void __iomem *sysc = (void __iomem *) KSEG1ADDR(MT7621_SYSC_BASE);