alpha: Primitive support for CPU power down.

Use WTINT to wait for the next interrupt.  Squash the WTINT call
if the PALcode doesn't support it (e.g. MILO).  No attempt is yet
made to skip clock ticks during normal scheduling in order to stay
in power down mode longer.

Signed-off-by: Richard Henderson <rth@twiddle.net>

diff --git a/arch/alpha/Kconfig b/arch/alpha/Kconfig
index a67b971..f9e84da 100644 (file)
--- a/arch/alpha/Kconfig
+++ b/arch/alpha/Kconfig
@@ -586,6 +586,30 @@ config NUMA
          Access).  This option is for configuring high-end multiprocessor
          server machines.  If in doubt, say N.
 
+config ALPHA_WTINT
+       bool "Use WTINT" if ALPHA_SRM || ALPHA_GENERIC
+       default y if ALPHA_QEMU
+       default n if ALPHA_EV5 || ALPHA_EV56 || (ALPHA_EV4 && !ALPHA_LCA)
+       default n if !ALPHA_SRM && !ALPHA_GENERIC
+       default y if SMP
+       ---help---
+         The Wait for Interrupt (WTINT) PALcall attempts to place the CPU
+         to sleep until the next interrupt.  This may reduce the power
+         consumed, and the heat produced by the computer.  However, it has
+         the side effect of making the cycle counter unreliable as a timing
+         device across the sleep.
+
+         For emulation under QEMU, definitely say Y here, as we have other
+         mechanisms for measuring time than the cycle counter.
+
+         For EV4 (but not LCA), EV5 and EV56 systems, or for systems running
+         MILO, sleep mode is not supported so you might as well say N here.
+
+         For SMP systems we cannot use the cycle counter for timing anyway,
+         so you might as well say Y here.
+
+         If unsure, say N.
+
 config NODES_SHIFT
        int
        default "7"

diff --git a/arch/alpha/include/asm/pal.h b/arch/alpha/include/asm/pal.h
index 6fcd2b5..e78ec9b 100644 (file)
--- a/arch/alpha/include/asm/pal.h
+++ b/arch/alpha/include/asm/pal.h
@@ -89,6 +89,7 @@ __CALL_PAL_W1(wrmces, unsigned long);
 __CALL_PAL_RW2(wrperfmon, unsigned long, unsigned long, unsigned long);
 __CALL_PAL_W1(wrusp, unsigned long);
 __CALL_PAL_W1(wrvptptr, unsigned long);
+__CALL_PAL_RW1(wtint, unsigned long, unsigned long);
 
 /*
  * TB routines..

diff --git a/arch/alpha/include/uapi/asm/pal.h b/arch/alpha/include/uapi/asm/pal.h
index 3c0ce08..dfc8140 100644 (file)
--- a/arch/alpha/include/uapi/asm/pal.h
+++ b/arch/alpha/include/uapi/asm/pal.h
@@ -46,6 +46,7 @@
 #define PAL_rdusp      58
 #define PAL_whami      60
 #define PAL_retsys     61
+#define PAL_wtint      62
 #define PAL_rti                63
 
 

diff --git a/arch/alpha/kernel/process.c b/arch/alpha/kernel/process.c
index f2360a7..1941a07 100644 (file)
--- a/arch/alpha/kernel/process.c
+++ b/arch/alpha/kernel/process.c
@@ -46,6 +46,23 @@
 void (*pm_power_off)(void) = machine_power_off;
 EXPORT_SYMBOL(pm_power_off);
 
+#ifdef CONFIG_ALPHA_WTINT
+/*
+ * Sleep the CPU.
+ * EV6, LCA45 and QEMU know how to power down, skipping N timer interrupts.
+ */
+void arch_cpu_idle(void)
+{
+       wtint(0);
+       local_irq_enable();
+}
+
+void arch_cpu_idle_dead(void)
+{
+       wtint(INT_MAX);
+}
+#endif /* ALPHA_WTINT */
+
 struct halt_info {
        int mode;
        char *restart_cmd;

diff --git a/arch/alpha/kernel/traps.c b/arch/alpha/kernel/traps.c
index bd0665c..9c4c189 100644 (file)
--- a/arch/alpha/kernel/traps.c
+++ b/arch/alpha/kernel/traps.c
@@ -241,6 +241,21 @@ do_entIF(unsigned long type, struct pt_regs *regs)
                               (const char *)(data[1] | (long)data[2] << 32), 
                               data[0]);
                }
+#ifdef CONFIG_ALPHA_WTINT
+               if (type == 4) {
+                       /* If CALL_PAL WTINT is totally unsupported by the
+                          PALcode, e.g. MILO, "emulate" it by overwriting
+                          the insn.  */
+                       unsigned int *pinsn
+                         = (unsigned int *) regs->pc - 1;
+                       if (*pinsn == PAL_wtint) {
+                               *pinsn = 0x47e01400; /* mov 0,$0 */
+                               imb();
+                               regs->r0 = 0;
+                               return;
+                       }
+               }
+#endif /* ALPHA_WTINT */
                die_if_kernel((type == 1 ? "Kernel Bug" : "Instruction fault"),
                              regs, type, NULL);
        }