kernel-ark/arch/mips/kernel/time.c

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/*
* Copyright 2001 MontaVista Software Inc.
* Author: Jun Sun, jsun@mvista.com or jsun@junsun.net
* Copyright (c) 2003, 2004 Maciej W. Rozycki
*
* Common time service routines for MIPS machines.
*
* This program is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License as published by the
* Free Software Foundation; either version 2 of the License, or (at your
* option) any later version.
*/
#include <linux/bug.h>
#include <linux/clockchips.h>
#include <linux/types.h>
#include <linux/kernel.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/param.h>
#include <linux/time.h>
#include <linux/timex.h>
#include <linux/smp.h>
#include <linux/spinlock.h>
#include <linux/export.h>
#include <asm/cpu-features.h>
#include <asm/cpu-type.h>
#include <asm/div64.h>
#include <asm/time.h>
/*
* forward reference
*/
DEFINE_SPINLOCK(rtc_lock);
EXPORT_SYMBOL(rtc_lock);
int __weak rtc_mips_set_time(unsigned long sec)
{
return 0;
}
int __weak rtc_mips_set_mmss(unsigned long nowtime)
{
return rtc_mips_set_time(nowtime);
}
int update_persistent_clock(struct timespec now)
{
return rtc_mips_set_mmss(now.tv_sec);
}
static int null_perf_irq(void)
{
return 0;
}
IRQ: Maintain regs pointer globally rather than passing to IRQ handlers Maintain a per-CPU global "struct pt_regs *" variable which can be used instead of passing regs around manually through all ~1800 interrupt handlers in the Linux kernel. The regs pointer is used in few places, but it potentially costs both stack space and code to pass it around. On the FRV arch, removing the regs parameter from all the genirq function results in a 20% speed up of the IRQ exit path (ie: from leaving timer_interrupt() to leaving do_IRQ()). Where appropriate, an arch may override the generic storage facility and do something different with the variable. On FRV, for instance, the address is maintained in GR28 at all times inside the kernel as part of general exception handling. Having looked over the code, it appears that the parameter may be handed down through up to twenty or so layers of functions. Consider a USB character device attached to a USB hub, attached to a USB controller that posts its interrupts through a cascaded auxiliary interrupt controller. A character device driver may want to pass regs to the sysrq handler through the input layer which adds another few layers of parameter passing. I've build this code with allyesconfig for x86_64 and i386. I've runtested the main part of the code on FRV and i386, though I can't test most of the drivers. I've also done partial conversion for powerpc and MIPS - these at least compile with minimal configurations. This will affect all archs. Mostly the changes should be relatively easy. Take do_IRQ(), store the regs pointer at the beginning, saving the old one: struct pt_regs *old_regs = set_irq_regs(regs); And put the old one back at the end: set_irq_regs(old_regs); Don't pass regs through to generic_handle_irq() or __do_IRQ(). In timer_interrupt(), this sort of change will be necessary: - update_process_times(user_mode(regs)); - profile_tick(CPU_PROFILING, regs); + update_process_times(user_mode(get_irq_regs())); + profile_tick(CPU_PROFILING); I'd like to move update_process_times()'s use of get_irq_regs() into itself, except that i386, alone of the archs, uses something other than user_mode(). Some notes on the interrupt handling in the drivers: (*) input_dev() is now gone entirely. The regs pointer is no longer stored in the input_dev struct. (*) finish_unlinks() in drivers/usb/host/ohci-q.c needs checking. It does something different depending on whether it's been supplied with a regs pointer or not. (*) Various IRQ handler function pointers have been moved to type irq_handler_t. Signed-Off-By: David Howells <dhowells@redhat.com> (cherry picked from 1b16e7ac850969f38b375e511e3fa2f474a33867 commit)
2006-10-05 13:55:46 +00:00
int (*perf_irq)(void) = null_perf_irq;
EXPORT_SYMBOL(perf_irq);
/*
* time_init() - it does the following things.
*
* 1) plat_time_init() -
* a) (optional) set up RTC routines,
* b) (optional) calibrate and set the mips_hpt_frequency
* (only needed if you intended to use cpu counter as timer interrupt
* source)
* 2) calculate a couple of cached variables for later usage
*/
unsigned int mips_hpt_frequency;
/*
* This function exists in order to cause an error due to a duplicate
* definition if platform code should have its own implementation. The hook
* to use instead is plat_time_init. plat_time_init does not receive the
* irqaction pointer argument anymore. This is because any function which
* initializes an interrupt timer now takes care of its own request_irq rsp.
* setup_irq calls and each clock_event_device should use its own
* struct irqrequest.
*/
void __init plat_timer_setup(void)
{
BUG();
}
static __init int cpu_has_mfc0_count_bug(void)
{
switch (current_cpu_type()) {
case CPU_R4000PC:
case CPU_R4000SC:
case CPU_R4000MC:
/*
* V3.0 is documented as suffering from the mfc0 from count bug.
* Afaik this is the last version of the R4000. Later versions
* were marketed as R4400.
*/
return 1;
case CPU_R4400PC:
case CPU_R4400SC:
case CPU_R4400MC:
/*
* The published errata for the R4400 up to 3.0 say the CPU
* has the mfc0 from count bug.
*/
if ((current_cpu_data.processor_id & 0xff) <= 0x30)
return 1;
/*
* we assume newer revisions are ok
*/
return 0;
}
return 0;
}
void __init time_init(void)
{
plat_time_init();
MIPS: R4k clock source initialization bug fix This is a fix for a bug introduced with commit 447cdf2628b59aa513a42785450b348dced26d8a, submitted as archived here: http://www.linux-mips.org/cgi-bin/mesg.cgi?a=linux-mips&i=20080312235002.c717dde3.yoichi_yuasa%40tripeaks.co.jp regrettably with no further explanation. The issue is with the CP0 Count register read erratum present on R4000 and some R4400 processors. If this erratum is present, then a read from this register that happens around the time it reaches the value stored in the CP0 Compare register causes a CP0 timer interrupt that is supposed to happen when the values in the two registers match to be missed. The implication for the chips affected is the CP0 timer can be used either as a source of a timer interrupt (a clock event) or as a source of a high-resolution counter (a clock source), but not both at a time. The erratum does not affect timer interrupt operation itself, because in this case the CP0 Count register is only read while the timer interrupt has already been raised, while high-resolution counter references happen at random times. Additionally some systems apparently have issues with the timer interrupt line being routed externally and not following the usual CP0 Count/Compare semantics. In this case we don't want to use the R4k clock event. We've meant to address the erratum and the timer interrupt routing issue in time_init, however the commit referred to above broke our solution. What we currently have is we enable the R4k clock source if the R4k clock event initialization has succeeded (the timer is present and has no timer interrupt routing issue) or there is no CP0 Count register read erratum. Which gives the following boolean matrix: clock event | count erratum => clock source ------------+---------------+-------------- 0 | 0 | 1 (OK) 0 | 1 | 0 (bug!) -> no interference, could use 1 | 0 | 1 (OK) 1 | 1 | 1 (bug!) -> can't use, interference What we want instead is to enable the R4k clock source if there is no CP0 Count register read erratum (obviously) or the R4k clock event initialization has *failed* -- because in the latter case we won't be using the timer interrupt anyway, so we don't care about any interference CP0 Count reads might cause with the interrupt. This corresponds to the following boolean matrix: clock event | count erratum => clock source ------------+---------------+-------------- 0 | 0 | 1 0 | 1 | 1 1 | 0 | 1 1 | 1 | 0 This is implemented here, effectively reverting the problematic commit, and a short explanation is given next to code modified so that the rationale is known to future readers and confusion is prevented from happening here again. It is worth noting that mips_clockevent_init returns 0 upon success while cpu_has_mfc0_count_bug returns 0 upon failure. This is because the former function returns an error code while the latter returns a boolean value. To signify the difference I have therefore chosen to compare the result of the former call explicitly against 0. Signed-off-by: Maciej W. Rozycki <macro@linux-mips.org> Signed-off-by: Ralf Baechle <ralf@linux-mips.org> Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/5799/
2013-09-03 00:29:58 +00:00
/*
* The use of the R4k timer as a clock event takes precedence;
* if reading the Count register might interfere with the timer
* interrupt, then we don't use the timer as a clock source.
* We may still use the timer as a clock source though if the
* timer interrupt isn't reliable; the interference doesn't
* matter then, because we don't use the interrupt.
*/
if (mips_clockevent_init() != 0 || !cpu_has_mfc0_count_bug())
init_mips_clocksource();
}