Subject: Re: [PATCH] powerpc: Add support for using doorbells for SMP IPI

From: Benjamin Herrenschmidt <[email-masked]>
Date: Mon, 23 Feb 2009 13:43:51 +1100

On Thu, 2009-02-12 at 17:54 -0600, Kumar Gala wrote:
> The e500mc supports the new msgsnd/doorbell mechanisms that were added in
> the Power ISA 2.05 architecture.  We use the normal level doorbell for
> doing SMP IPIs at this point.

Any reason why you don't use the tag ? I'm not too familiar with the
doorbell stuff just yet but can't you use that instead of doing those
atomics ?

On thing we also need to look at is change our low level msg send to
take a CPU mask.

This will be better generically and we need a good cpu mask based IPI
for the TLB stuff anyway. Volunteer ? :-)

Cheers,
Ben.

> Signed-off-by: Kumar Gala <[email-masked]>
> ---
>  arch/powerpc/include/asm/cputable.h  |    4 ++-
>  arch/powerpc/include/asm/dbell.h     |   43 +++++++++++++++++++++++++++++++++
>  arch/powerpc/kernel/Makefile         |    2 +-
>  arch/powerpc/kernel/dbell.c          |   44 ++++++++++++++++++++++++++++++++++
>  arch/powerpc/kernel/head_fsl_booke.S |    6 ++++-
>  arch/powerpc/kernel/traps.c          |   21 ++++++++++++++++
>  6 files changed, 117 insertions(+), 3 deletions(-)
>  create mode 100644 arch/powerpc/include/asm/dbell.h
>  create mode 100644 arch/powerpc/kernel/dbell.c
> 
> diff --git a/arch/powerpc/include/asm/cputable.h b/arch/powerpc/include/asm/cputable.h
> index 4911104..fca1611 100644
> --- a/arch/powerpc/include/asm/cputable.h
> +++ b/arch/powerpc/include/asm/cputable.h
> @@ -145,6 +145,7 @@ extern const char *powerpc_base_platform;
>  #define CPU_FTR_USE_TB			ASM_CONST(0x0000000000000040)
>  #define CPU_FTR_L2CSR			ASM_CONST(0x0000000000000080)
>  #define CPU_FTR_601			ASM_CONST(0x0000000000000100)
> +#define CPU_FTR_DBELL			ASM_CONST(0x0000000000000200)
>  #define CPU_FTR_CAN_NAP			ASM_CONST(0x0000000000000400)
>  #define CPU_FTR_L3CR			ASM_CONST(0x0000000000000800)
>  #define CPU_FTR_L3_DISABLE_NAP		ASM_CONST(0x0000000000001000)
> @@ -373,7 +374,8 @@ extern const char *powerpc_base_platform;
>  	    CPU_FTR_NODSISRALIGN | CPU_FTR_NOEXECUTE)
>  #define CPU_FTRS_E500MC	(CPU_FTR_MAYBE_CAN_DOZE | CPU_FTR_USE_TB | \
>  	    CPU_FTR_MAYBE_CAN_NAP | CPU_FTR_NODSISRALIGN | \
> -	    CPU_FTR_L2CSR | CPU_FTR_LWSYNC | CPU_FTR_NOEXECUTE)
> +	    CPU_FTR_L2CSR | CPU_FTR_LWSYNC | CPU_FTR_NOEXECUTE | \
> +	    CPU_FTR_DBELL)
>  #define CPU_FTRS_GENERIC_32	(CPU_FTR_COMMON | CPU_FTR_NODSISRALIGN)
>  
>  /* 64-bit CPUs */
> diff --git a/arch/powerpc/include/asm/dbell.h b/arch/powerpc/include/asm/dbell.h
> new file mode 100644
> index 0000000..501189a
> --- /dev/null
> +++ b/arch/powerpc/include/asm/dbell.h
> @@ -0,0 +1,43 @@
> +/*
> + * Copyright 2009 Freescale Semicondutor, Inc.
> + *
> + * 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.
> + *
> + * provides masks and opcode images for use by code generation, emulation
> + * and for instructions that older assemblers might not know about
> + */
> +#ifndef _ASM_POWERPC_DBELL_H
> +#define _ASM_POWERPC_DBELL_H
> +
> +#include <linux/smp.h>
> +#include <linux/threads.h>
> +
> +#include <asm/ppc-opcode.h>
> +
> +#define PPC_DBELL_MSG_BRDCAST	(0x04000000)
> +#define PPC_DBELL_TYPE(x)	(((x) & 0xf) << 28)
> +enum ppc_dbell {
> +	PPC_DBELL = 0,		/* doorbell */
> +	PPC_DBELL_CRIT = 1,	/* critical doorbell */
> +	PPC_G_DBELL = 2,	/* guest doorbell */
> +	PPC_G_DBELL_CRIT = 3,	/* guest critical doorbell */
> +	PPC_G_DBELL_MC = 4,	/* guest mcheck doorbell */
> +};
> +
> +#ifdef CONFIG_SMP
> +extern unsigned long dbell_smp_message[NR_CPUS];
> +extern void smp_dbell_message_pass(int target, int msg);
> +#endif
> +
> +static inline void ppc_msgsnd(enum ppc_dbell type, u32 flags, u32 tag)
> +{
> +	u32 msg = PPC_DBELL_TYPE(type) | (flags & PPC_DBELL_MSG_BRDCAST) |
> +			(tag & 0x07ffffff);
> +
> +	__asm__ __volatile__ (PPC_MSGSND(%0) : : "r" (msg));
> +}
> +
> +#endif /* _ASM_POWERPC_DBELL_H */
> diff --git a/arch/powerpc/kernel/Makefile b/arch/powerpc/kernel/Makefile
> index d159921..f420844 100644
> --- a/arch/powerpc/kernel/Makefile
> +++ b/arch/powerpc/kernel/Makefile
> @@ -61,7 +61,7 @@ obj-$(CONFIG_HIBERNATION)	+= swsusp.o suspend.o \
>  obj64-$(CONFIG_HIBERNATION)	+= swsusp_asm64.o
>  obj-$(CONFIG_MODULES)		+= module.o module_$(CONFIG_WORD_SIZE).o
>  obj-$(CONFIG_44x)		+= cpu_setup_44x.o
> -obj-$(CONFIG_FSL_BOOKE)		+= cpu_setup_fsl_booke.o
> +obj-$(CONFIG_FSL_BOOKE)		+= cpu_setup_fsl_booke.o dbell.o
>  
>  extra-$(CONFIG_PPC_STD_MMU)	:= head_32.o
>  extra-$(CONFIG_PPC64)		:= head_64.o
> diff --git a/arch/powerpc/kernel/dbell.c b/arch/powerpc/kernel/dbell.c
> new file mode 100644
> index 0000000..1493734
> --- /dev/null
> +++ b/arch/powerpc/kernel/dbell.c
> @@ -0,0 +1,44 @@
> +/*
> + * Author: Kumar Gala <[email-masked]>
> + *
> + * Copyright 2009 Freescale Semiconductor Inc.
> + *
> + * 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/stddef.h>
> +#include <linux/kernel.h>
> +#include <linux/smp.h>
> +#include <linux/threads.h>
> +
> +#include <asm/dbell.h>
> +
> +#ifdef CONFIG_SMP
> +unsigned long dbell_smp_message[NR_CPUS];
> +
> +void smp_dbell_message_pass(int target, int msg)
> +{
> +	int i;
> +
> +	if(target < NR_CPUS) {
> +		set_bit(msg, &dbell_smp_message[target]);
> +		ppc_msgsnd(PPC_DBELL, 0, target);
> +	}
> +	else if(target == MSG_ALL_BUT_SELF) {
> +		for_each_online_cpu(i) {
> +			if (i == smp_processor_id())
> +				continue;
> +			set_bit(msg, &dbell_smp_message[i]);
> +			ppc_msgsnd(PPC_DBELL, 0, i);
> +		}
> +	}
> +	else { /* target == MSG_ALL */
> +		for_each_online_cpu(i)
> +			set_bit(msg, &dbell_smp_message[i]);
> +		ppc_msgsnd(PPC_DBELL, PPC_DBELL_MSG_BRDCAST, 0);
> +	}
> +}
> +#endif
> diff --git a/arch/powerpc/kernel/head_fsl_booke.S b/arch/powerpc/kernel/head_fsl_booke.S
> index 4ea6e1a..4c22620 100644
> --- a/arch/powerpc/kernel/head_fsl_booke.S
> +++ b/arch/powerpc/kernel/head_fsl_booke.S
> @@ -698,7 +698,9 @@ interrupt_base:
>  	/* Performance Monitor */
>  	EXCEPTION(0x2060, PerformanceMonitor, performance_monitor_exception, EXC_XFER_STD)
>  
> -	EXCEPTION(0x2070, Doorbell, unknown_exception, EXC_XFER_STD)
> +	EXCEPTION(0x2070, Doorbell, doorbell_exception, EXC_XFER_STD)
> +
> +	CRITICAL_EXCEPTION(0x2080, CriticalDoorbell, unknown_exception)
>  
>  	/* Debug Interrupt */
>  	DEBUG_DEBUG_EXCEPTION
> @@ -921,6 +923,8 @@ _GLOBAL(__setup_e500mc_ivors)
>  	mtspr	SPRN_IVOR35,r3
>  	li	r3,Doorbell@l
>  	mtspr	SPRN_IVOR36,r3
> +	li	r3,CriticalDoorbell@l
> +	mtspr	SPRN_IVOR37,r3
>  	sync
>  	blr
>  
> diff --git a/arch/powerpc/kernel/traps.c b/arch/powerpc/kernel/traps.c
> index 970d66e..678fbff 100644
> --- a/arch/powerpc/kernel/traps.c
> +++ b/arch/powerpc/kernel/traps.c
> @@ -53,6 +53,9 @@
>  #endif
>  #include <asm/kexec.h>
>  #include <asm/ppc-opcode.h>
> +#ifdef CONFIG_FSL_BOOKE
> +#include <asm/dbell.h>
> +#endif
>  
>  #if defined(CONFIG_DEBUGGER) || defined(CONFIG_KEXEC)
>  int (*__debugger)(struct pt_regs *regs);
> @@ -1122,6 +1125,24 @@ void vsx_assist_exception(struct pt_regs *regs)
>  #endif /* CONFIG_VSX */
>  
>  #ifdef CONFIG_FSL_BOOKE
> +
> +void doorbell_exception(struct pt_regs *regs)
> +{
> +#ifdef CONFIG_SMP
> +	int cpu = smp_processor_id();
> +	int msg;
> +
> +	if (num_online_cpus() < 2)
> +		return;
> +
> +	for (msg = 0; msg < 4; msg++)
> +		if (test_and_clear_bit(msg, &dbell_smp_message[cpu]))
> +			smp_message_recv(msg);
> +#else
> +	printk(KERN_WARNING "Received doorbell on non-smp system\n");
> +#endif
> +}
> +
>  void CacheLockingException(struct pt_regs *regs, unsigned long address,
>  			   unsigned long error_code)
>  {