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alpha: Primitive support for CPU power down.

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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>
This commit is contained in:
Richard Henderson 2013-07-12 09:36:21 -07:00 committed by Matt Turner
parent fddd87d6e1
commit 7f3bbb82e0
5 changed files with 58 additions and 0 deletions
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24
arch/alpha/Kconfig
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@ -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"

1
arch/alpha/include/asm/pal.h
View File

@ -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..

1
arch/alpha/include/uapi/asm/pal.h
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@ -46,6 +46,7 @@
#define PAL_rdusp 58
#define PAL_whami 60
#define PAL_retsys 61
#define PAL_wtint 62
#define PAL_rti 63

17
arch/alpha/kernel/process.c
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@ -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;

15
arch/alpha/kernel/traps.c
View File

@ -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);
}