ARC: Allow SMP kernel to build/boot on UP-only infrastructure

In light of recent SNAFU with SMP build, allow simple platform to build
as SMP but run UP.

* Remove the dependence on simulation SMP extension to enable quick
  build/test iterations of SMP kernel.

* In absence of platform SMP registration, prevent the NULL smp feature
  name from borkign the system

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

arch/arc/include/asm/smp.h

@@ -59,7 +59,15 @@ struct plat_smp_ops {
 /* TBD: stop exporting it for direct population by platform */
 extern struct plat_smp_ops  plat_smp_ops;
 
-#endif  /* CONFIG_SMP */
+#else /* CONFIG_SMP */
+
+static inline void smp_init_cpus(void) {}
+static inline const char *arc_platform_smp_cpuinfo(void)
+{
+	return "";
+}
+
+#endif  /* !CONFIG_SMP */
 
 /*
  * ARC700 doesn't support atomic Read-Modify-Write ops.

arch/arc/kernel/setup.c

@@ -24,6 +24,7 @@
 #include <asm/unwind.h>
 #include <asm/clk.h>
 #include <asm/mach_desc.h>
+#include <asm/smp.h>
 
 #define FIX_PTR(x)  __asm__ __volatile__(";" : "+r"(x))
 
@@ -306,10 +307,7 @@ void setup_processor(void)
 	arc_chk_ccms();
 
 	printk(arc_extn_mumbojumbo(cpu_id, str, sizeof(str)));
-
-#ifdef CONFIG_SMP
 	printk(arc_platform_smp_cpuinfo());
-#endif
 
 	arc_chk_fpu();
 }
@@ -360,11 +358,7 @@ void __init setup_arch(char **cmdline_p)
 		machine_desc->init_early();
 
 	setup_processor();
-
-#ifdef CONFIG_SMP
 	smp_init_cpus();
-#endif
-
 	setup_arch_memory();
 
 	/* copy flat DT out of .init and then unflatten it */
@@ -424,14 +418,9 @@ static int show_cpuinfo(struct seq_file *m, void *v)
 		   (loops_per_jiffy / (5000 / HZ)) % 100);
 
 	seq_printf(m, arc_mmu_mumbojumbo(cpu_id, str, PAGE_SIZE));
-
 	seq_printf(m, arc_cache_mumbojumbo(cpu_id, str, PAGE_SIZE));
-
 	seq_printf(m, arc_extn_mumbojumbo(cpu_id, str, PAGE_SIZE));
-
-#ifdef CONFIG_SMP
 	seq_printf(m, arc_platform_smp_cpuinfo());
-#endif
 
 	free_page((unsigned long)str);
 done:

arch/arc/kernel/smp.c

@@ -101,7 +101,7 @@ void __weak arc_platform_smp_wait_to_boot(int cpu)
 
 const char *arc_platform_smp_cpuinfo(void)
 {
-	return plat_smp_ops.info;
+	return plat_smp_ops.info ? : "";
 }
 
 /*

arch/arc/plat-arcfpga/Kconfig

@@ -8,7 +8,7 @@
 
 menuconfig ARC_PLAT_FPGA_LEGACY
 	bool "\"Legacy\" ARC FPGA dev Boards"
-	select ISS_SMP_EXTN if SMP
+	select ARC_HAS_COH_CACHES if SMP
 	help
 	  Support for ARC development boards, provided by Synopsys.
 	  These are based on FPGA or ISS. e.g.

arch/arc/plat-arcfpga/platform.c

@@ -71,7 +71,7 @@ MACHINE_START(ML509, "ml509")
 	.dt_compat	= ml509_compat,
 	.init_early	= plat_fpga_early_init,
 	.init_machine	= plat_fpga_populate_dev,
-#ifdef CONFIG_SMP
+#ifdef CONFIG_ISS_SMP_EXTN
 	.init_smp	= iss_model_init_smp,
 #endif
 MACHINE_END