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 a67b971c830a77c7651c52d89e9562d10ccea964..f9e84da49716dd0c71ba0625788713e9f0c52ace 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 6fcd2b5b08f0d5ac4462ba6616a66519c2819d7d..e78ec9bcc768a88d2e330b3bc855fe384cb52bb1 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 3c0ce08e5f592d9b779c10a441527cd9061e9c07..dfc8140b908821d46a3d82f30baaa121c1bf64ef 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 f2360a74e5d5544983160d951c46bddb98819e0e..1941a07b5811f925aed82e853aab4efb081f74ca 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 bd0665cdc840d3e9a79b752ec3a88279ede69344..9c4c189eb22f5a9db2d2ae678756a5241b3e1ee5 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);
        }