[PATCH RFC] Interface to set SPRN_TIDR
From: Sukadev Bhattiprolu <hidden>
Date: 2017-08-30 02:39:04
We need the SPRN_TIDR to be set for use with fast thread-wakeup (core-to-core wakeup) in VAS. Each user thread that has a receive window setup and expects to be notified when a sender issues a paste needs to have a unique SPRN_TIDR value. The SPRN_TIDR value only needs to unique within the process but for now we use a globally unique thread id as described below. Signed-off-by: Sukadev Bhattiprolu <redacted> --- Changelog[v2] - Michael Ellerman: Use an interface to assign TIDR so it is assigned to only threads that need it; move assignment to restore_sprs(). Drop lint from rebase; arch/powerpc/include/asm/processor.h | 4 ++ arch/powerpc/include/asm/switch_to.h | 3 ++ arch/powerpc/kernel/process.c | 97 ++++++++++++++++++++++++++++++++++++ 3 files changed, 104 insertions(+)
diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
index fab7ff8..bf6ba63 100644
--- a/arch/powerpc/include/asm/processor.h
+++ b/arch/powerpc/include/asm/processor.h@@ -232,6 +232,10 @@ struct debug_reg { struct thread_struct { unsigned long ksp; /* Kernel stack pointer */ +#ifdef CONFIG_PPC_VAS + unsigned long tidr; +#endif + #ifdef CONFIG_PPC64 unsigned long ksp_vsid; #endif
diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
index 17c8380..4962455 100644
--- a/arch/powerpc/include/asm/switch_to.h
+++ b/arch/powerpc/include/asm/switch_to.h@@ -91,4 +91,7 @@ static inline void clear_task_ebb(struct task_struct *t) #endif } +extern void set_thread_tidr(struct task_struct *t); +extern void clear_thread_tidr(struct task_struct *t); + #endif /* _ASM_POWERPC_SWITCH_TO_H */
diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
index 1f0fd36..13abb22 100644
--- a/arch/powerpc/kernel/process.c
+++ b/arch/powerpc/kernel/process.c@@ -1132,6 +1132,10 @@ static inline void restore_sprs(struct thread_struct *old_thread, mtspr(SPRN_TAR, new_thread->tar); } #endif +#ifdef CONFIG_PPC_VAS + if (old_thread->tidr != new_thread->tidr) + mtspr(SPRN_TIDR, new_thread->tidr); +#endif } #ifdef CONFIG_PPC_BOOK3S_64
@@ -1446,9 +1450,97 @@ void flush_thread(void) #endif /* CONFIG_HAVE_HW_BREAKPOINT */ } +#ifdef CONFIG_PPC_VAS +static DEFINE_SPINLOCK(vas_thread_id_lock); +static DEFINE_IDA(vas_thread_ida); + +/* + * We need to assign an unique thread id to each thread in a process. This + * thread id is intended to be used with the Fast Thread-wakeup (aka Core- + * to-core wakeup) mechanism being implemented on top of Virtual Accelerator + * Switchboard (VAS). + * + * To get a unique thread-id per process we could simply use task_pid_nr() + * but the problem is that task_pid_nr() is not yet available for the thread + * when copy_thread() is called. Fixing that would require changing more + * intrusive arch-neutral code in code path in copy_process()?. + * + * Further, to assign unique thread ids within each process, we need an + * atomic field (or an IDR) in task_struct, which again intrudes into the + * arch-neutral code. + * + * So try to assign globally unique thraed ids for now. + * + * NOTE: TIDR 0 indicates that the thread does not need a TIDR value. + * For now, only threads that expect to be notified by the VAS + * hardware need a TIDR value and we assign values > 0 for those. + */ +#define MAX_THREAD_CONTEXT ((1 << 15) - 2) +static int assign_thread_tidr(void) +{ + int index; + int err; + +again: + if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL)) + return -ENOMEM; + + spin_lock(&vas_thread_id_lock); + err = ida_get_new_above(&vas_thread_ida, 1, &index); + spin_unlock(&vas_thread_id_lock); + + if (err == -EAGAIN) + goto again; + else if (err) + return err; + + if (index > MAX_THREAD_CONTEXT) { + spin_lock(&vas_thread_id_lock); + ida_remove(&vas_thread_ida, index); + spin_unlock(&vas_thread_id_lock); + return -ENOMEM; + } + + return index; +} + +static void free_thread_tidr(int id) +{ + spin_lock(&vas_thread_id_lock); + ida_remove(&vas_thread_ida, id); + spin_unlock(&vas_thread_id_lock); +} + +void clear_thread_tidr(struct task_struct *t) +{ + if (t->thread.tidr) { + free_thread_tidr(t->thread.tidr); + t->thread.tidr = 0; + mtspr(SPRN_TIDR, 0); + } +} + +/* + * Assign an unique thread id for this thread and set it in the + * thread structure. For now, we need this interface only for + * the current task. + */ +void set_thread_tidr(struct task_struct *t) +{ + WARN_ON(t != current); + t->thread.tidr = assign_thread_tidr(); + mtspr(SPRN_TIDR, t->thread.tidr); +} + +#endif /* CONFIG_PPC_VAS */ + + void release_thread(struct task_struct *t) { +#ifdef CONFIG_PPC_VAS + clear_thread_tidr(t); +#endif } /*
@@ -1474,6 +1566,8 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) clear_task_ebb(dst); + dst->thread.tidr = 0; + return 0; }
@@ -1584,6 +1678,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp, #endif setup_ksp_vsid(p, sp); +#ifdef CONFIG_PPC_VAS + p->thread.tidr = 0; +#endif #ifdef CONFIG_PPC64 if (cpu_has_feature(CPU_FTR_DSCR)) {
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2.7.4