arch/riscv: Implement cpuid mapping

Implement hartid<->cpuid mapping for RISC-V. This is necessary for some
platforms which cannot use 1:1 mapping between logical and physical CPU /
core IDs. One example is MPFS where hart0 cannot be used for NuttX SMP as
it is a less capable "monitor" core (E51) compared to the application
cores hart1...3 (E54).

Why not just use a generic offset then? We also need the physical hart ID
for many things:
- Communication between harts (IPI)
- External interrupt acknowledgment (interrupt claim for specific CPU)
- Communication to SBI

Thus, create procedures that can do this translation:
- The default mapping is still logical=physical.
- Another flavor is to use the existing CONFIG_ARCH_RV_HARTID_BASE config
  variable, which is just a simple offset
- The final flavor is to overload hartid<->cpuid on a per chip basis (no
  example for this is provided yet)

arch/Kconfig

@@ -95,6 +95,7 @@ config ARCH_RISCV
 	select ARCH_HAVE_THREAD_LOCAL
 	select ARCH_HAVE_POWEROFF
 	select ARCH_HAVE_LAZYFPU if ARCH_HAVE_FPU
+	select ARCH_HAVE_CPUID_MAPPING if ARCH_HAVE_MULTICPU
 	---help---
 		RISC-V 32 and 64-bit RV32 / RV64 architectures.
 

arch/risc-v/include/irq.h

@@ -709,14 +709,25 @@ irqstate_t up_irq_enable(void);
 int up_cpu_index(void) noinstrument_function;
 #endif /* CONFIG_ARCH_HAVE_MULTICPU */
 
+/****************************************************************************
+ * Name: up_this_cpu
+ *
+ * Description:
+ *   Return the logical core number. Default implementation is 1:1 mapping,
+ *   i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int up_this_cpu(void);
+
 /****************************************************************************
  * Inline Functions
  ****************************************************************************/
 
 static inline_function uintreg_t *up_current_regs(void)
 {
 #ifdef CONFIG_SMP
-  return (uintreg_t *)g_current_regs[up_cpu_index()];
+  return (uintreg_t *)g_current_regs[up_this_cpu()];
 #else
   return (uintreg_t *)g_current_regs[0];
 #endif
@@ -725,7 +736,7 @@ static inline_function uintreg_t *up_current_regs(void)
 static inline_function void up_set_current_regs(uintreg_t *regs)
 {
 #ifdef CONFIG_SMP
-  g_current_regs[up_cpu_index()] = regs;
+  g_current_regs[up_this_cpu()] = regs;
 #else
   g_current_regs[0] = regs;
 #endif

arch/risc-v/src/common/riscv_cpuindex.c

@@ -45,5 +45,47 @@
 
 int up_cpu_index(void)
 {
-  return (int)riscv_mhartid() - CONFIG_ARCH_RV_HARTID_BASE;
+  return (int)riscv_mhartid();
+}
+
+/****************************************************************************
+ * Name: up_this_cpu
+ *
+ * Description:
+ *   Return the logical core number. Default implementation is 1:1 mapping,
+ *   i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int up_this_cpu(void)
+{
+  return riscv_hartid_to_cpuid((int)riscv_mhartid());
+}
+
+/****************************************************************************
+ * Name: riscv_hartid_to_cpuid
+ *
+ * Description:
+ *   Convert physical core number to logical core number. Default
+ *   implementation is 1:1 mapping, i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int weak_function riscv_hartid_to_cpuid(int cpu)
+{
+  return cpu + CONFIG_ARCH_RV_HARTID_BASE;
+}
+
+/****************************************************************************
+ * Name: riscv_cpuid_to_hartid
+ *
+ * Description:
+ *   Convert logical core number to physical core number. Default
+ *   implementation is 1:1 mapping, i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int weak_function riscv_cpuid_to_hartid(int cpu)
+{
+  return cpu - CONFIG_ARCH_RV_HARTID_BASE;
 }

arch/risc-v/src/common/riscv_cpustart.c

@@ -86,7 +86,7 @@ void riscv_cpu_boot(int cpu)
 #ifdef CONFIG_RISCV_PERCPU_SCRATCH
   /* Initialize the per CPU areas */
 
-  riscv_percpu_add_hart((uintptr_t)cpu);
+  riscv_percpu_add_hart(riscv_cpuid_to_hartid(cpu));
 #endif
 
 #ifdef CONFIG_BUILD_KERNEL

arch/risc-v/src/common/riscv_internal.h

@@ -427,6 +427,28 @@ int riscv_smp_call_handler(int irq, void *c, void *arg);
 
 uintptr_t riscv_mhartid(void);
 
+/****************************************************************************
+ * Name: riscv_hartid_to_cpuid
+ *
+ * Description:
+ *   Convert physical core number to logical core number. Default
+ *   implementation is 1:1 mapping, i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int riscv_hartid_to_cpuid(int cpu);
+
+/****************************************************************************
+ * Name: riscv_cpuid_to_hartid
+ *
+ * Description:
+ *   Convert logical core number to physical core number. Default
+ *   implementation is 1:1 mapping, i.e. physical=logical.
+ *
+ ****************************************************************************/
+
+int riscv_cpuid_to_hartid(int cpu);
+
 /* If kernel runs in Supervisor mode, a system call trampoline is needed */
 
 #ifdef CONFIG_ARCH_USE_S_MODE

arch/risc-v/src/common/riscv_ipi.h

@@ -36,9 +36,9 @@
 static inline void riscv_ipi_send(int cpu)
 {
 #if defined(CONFIG_ARCH_USE_S_MODE)
-  riscv_sbi_send_ipi(0x1, cpu);
+  riscv_sbi_send_ipi(0x1, riscv_cpuid_to_hartid(cpu));
 #elif defined(RISCV_IPI)
-  putreg32(1, (uintptr_t)RISCV_IPI + (4 * cpu));
+  putreg32(1, (uintptr_t)RISCV_IPI + (4 * riscv_cpuid_to_hartid(cpu)));
 #else
 #  error "No IPI support for this SoC"
 #endif
@@ -47,7 +47,7 @@ static inline void riscv_ipi_send(int cpu)
 static inline void riscv_ipi_clear(int cpu)
 {
 #if defined(RISCV_IPI) && !defined(CONFIG_ARCH_USE_S_MODE)
-  putreg32(0, (uintptr_t)RISCV_IPI + (4 * cpu));
+  putreg32(0, (uintptr_t)RISCV_IPI + (4 * riscv_cpuid_to_hartid(cpu)));
 #endif
   CLEAR_CSR(CSR_IP, IP_SIP);
 }