From f97bb36f705da0a86b3ea77bfeee3415fee0b025 Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Tue, 16 Jun 2009 16:42:49 +0000 Subject: powerpc/rtas: Turn rtas lock into a raw spinlock RTAS currently uses a normal spinlock. However it can be called from contexts where this is not necessarily a good idea. For example, it can be called while syncing timebases, with the core timebase being frozen. Unfortunately, that will deadlock in case of lock contention when spinlock debugging is enabled as the spin lock debugging code will try to use __delay() which ... relies on the timebase being enabled. Also RTAS can be used in some low level IRQ handling code path so it may as well be a raw spinlock for -rt sake. Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/rtas.c | 38 +++++++++++++++++++++++++++++--------- 1 file changed, 29 insertions(+), 9 deletions(-) (limited to 'arch/powerpc/kernel/rtas.c') diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index ee4c7609b649..d9a9974c6938 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -40,7 +40,7 @@ #include struct rtas_t rtas = { - .lock = SPIN_LOCK_UNLOCKED + .lock = __RAW_SPIN_LOCK_UNLOCKED }; EXPORT_SYMBOL(rtas); @@ -67,6 +67,28 @@ unsigned long rtas_rmo_buf; void (*rtas_flash_term_hook)(int); EXPORT_SYMBOL(rtas_flash_term_hook); +/* RTAS use home made raw locking instead of spin_lock_irqsave + * because those can be called from within really nasty contexts + * such as having the timebase stopped which would lockup with + * normal locks and spinlock debugging enabled + */ +static unsigned long lock_rtas(void) +{ + unsigned long flags; + + local_irq_save(flags); + preempt_disable(); + __raw_spin_lock_flags(&rtas.lock, flags); + return flags; +} + +static void unlock_rtas(unsigned long flags) +{ + __raw_spin_unlock(&rtas.lock); + local_irq_restore(flags); + preempt_enable(); +} + /* * call_rtas_display_status and call_rtas_display_status_delay * are designed only for very early low-level debugging, which @@ -79,7 +101,7 @@ static void call_rtas_display_status(char c) if (!rtas.base) return; - spin_lock_irqsave(&rtas.lock, s); + s = lock_rtas(); args->token = 10; args->nargs = 1; @@ -89,7 +111,7 @@ static void call_rtas_display_status(char c) enter_rtas(__pa(args)); - spin_unlock_irqrestore(&rtas.lock, s); + unlock_rtas(s); } static void call_rtas_display_status_delay(char c) @@ -411,8 +433,7 @@ int rtas_call(int token, int nargs, int nret, int *outputs, ...) if (!rtas.entry || token == RTAS_UNKNOWN_SERVICE) return -1; - /* Gotta do something different here, use global lock for now... */ - spin_lock_irqsave(&rtas.lock, s); + s = lock_rtas(); rtas_args = &rtas.args; rtas_args->token = token; @@ -439,8 +460,7 @@ int rtas_call(int token, int nargs, int nret, int *outputs, ...) outputs[i] = rtas_args->rets[i+1]; ret = (nret > 0)? rtas_args->rets[0]: 0; - /* Gotta do something different here, use global lock for now... */ - spin_unlock_irqrestore(&rtas.lock, s); + unlock_rtas(s); if (buff_copy) { log_error(buff_copy, ERR_TYPE_RTAS_LOG, 0); @@ -837,7 +857,7 @@ asmlinkage int ppc_rtas(struct rtas_args __user *uargs) buff_copy = get_errorlog_buffer(); - spin_lock_irqsave(&rtas.lock, flags); + flags = lock_rtas(); rtas.args = args; enter_rtas(__pa(&rtas.args)); @@ -848,7 +868,7 @@ asmlinkage int ppc_rtas(struct rtas_args __user *uargs) if (args.rets[0] == -1) errbuf = __fetch_rtas_last_error(buff_copy); - spin_unlock_irqrestore(&rtas.lock, flags); + unlock_rtas(flags); if (buff_copy) { if (errbuf) -- cgit v1.2.3 From c4007a2fbf5f82b7e694c22b5929c87e38415a56 Mon Sep 17 00:00:00 2001 From: Benjamin Herrenschmidt Date: Tue, 16 Jun 2009 16:42:50 +0000 Subject: powerpc: Use one common impl. of RTAS timebase sync and use raw spinlock Several platforms use their own copy of what is essentially the same code, using RTAS to synchronize the timebases when bringing up new CPUs. This moves it all into a single common implementation and additionally turns the spinlock into a raw spinlock since the former can rely on the timebase not being frozen when spinlock debugging is enabled, and finally masks interrupts while the timebase is disabled. Signed-off-by: Benjamin Herrenschmidt --- arch/powerpc/kernel/rtas.c | 31 +++++++++++++++++++++++++++++++ 1 file changed, 31 insertions(+) (limited to 'arch/powerpc/kernel/rtas.c') diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c index d9a9974c6938..c434823b8c83 100644 --- a/arch/powerpc/kernel/rtas.c +++ b/arch/powerpc/kernel/rtas.c @@ -38,6 +38,7 @@ #include #include #include +#include struct rtas_t rtas = { .lock = __RAW_SPIN_LOCK_UNLOCKED @@ -971,3 +972,33 @@ int __init early_init_dt_scan_rtas(unsigned long node, /* break now */ return 1; } + +static raw_spinlock_t timebase_lock; +static u64 timebase = 0; + +void __cpuinit rtas_give_timebase(void) +{ + unsigned long flags; + + local_irq_save(flags); + hard_irq_disable(); + __raw_spin_lock(&timebase_lock); + rtas_call(rtas_token("freeze-time-base"), 0, 1, NULL); + timebase = get_tb(); + __raw_spin_unlock(&timebase_lock); + + while (timebase) + barrier(); + rtas_call(rtas_token("thaw-time-base"), 0, 1, NULL); + local_irq_restore(flags); +} + +void __cpuinit rtas_take_timebase(void) +{ + while (!timebase) + barrier(); + __raw_spin_lock(&timebase_lock); + set_tb(timebase >> 32, timebase & 0xffffffff); + timebase = 0; + __raw_spin_unlock(&timebase_lock); +} -- cgit v1.2.3