[U-Boot] [PATCH v2 1/9] riscv: add infrastructure for calling functions on other harts

[Atish Patra <atish.patra@wdc.com>]

On 3/5/19 2:54 PM, Lukas Auer wrote:
> Harts on RISC-V boot independently, U-Boot is responsible for managing
> them. Functions are called on other harts with smp_call_function(),
> which sends inter-processor interrupts (IPIs) to all other available
> harts. Available harts are those marked as available in the device tree
> and present in the available_harts mask stored in global data. The
> available_harts mask is used to register all harts that have entered
> U-Boot. Functions are specified with their address and two function
> arguments (argument 2 and 3). The first function argument is always the
> hart ID of the hart calling the function. On the other harts, the IPI
> interrupt handler handle_ipi() must be called on software interrupts to
> handle the request and call the specified function.
> 
> Functions are stored in the ipi_data data structure. Every hart has its
> own data structure in global data. While this is not required at the
> moment (all harts are expected to boot Linux), this does allow future
> expansion, where other harts may be used for monitoring or other tasks.
> 
> Signed-off-by: Lukas Auer <lukas.auer@aisec.fraunhofer.de>
> ---
> 
> Changes in v2:
> - Remove unneeded quotes from NR_CPUS Kconfig entry
> - Move memory barrier from send_ipi_many() to handle_ipi()
> - Add check in send_ipi_many so that IPIs are only sent to available
> harts as indicated by the available_harts mask
> 
>   arch/riscv/Kconfig                   |  19 +++++
>   arch/riscv/include/asm/global_data.h |   6 ++
>   arch/riscv/include/asm/smp.h         |  53 ++++++++++++
>   arch/riscv/lib/Makefile              |   1 +
>   arch/riscv/lib/smp.c                 | 116 +++++++++++++++++++++++++++
>   5 files changed, 195 insertions(+)
>   create mode 100644 arch/riscv/include/asm/smp.h
>   create mode 100644 arch/riscv/lib/smp.c
> 
> diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> index 36512a8995..4d7a115569 100644
> --- a/arch/riscv/Kconfig
> +++ b/arch/riscv/Kconfig
> @@ -120,4 +120,23 @@ config RISCV_RDTIME
>   config SYS_MALLOC_F_LEN
>   	default 0x1000
>   
> +config SMP
> +	bool "Symmetric Multi-Processing"
> +	help
> +	  This enables support for systems with more than one CPU. If
> +	  you say N here, U-Boot will run on single and multiprocessor
> +	  machines, but will use only one CPU of a multiprocessor
> +	  machine. If you say Y here, U-Boot will run on many, but not
> +	  all, single processor machines.
> +
> +config NR_CPUS
> +	int "Maximum number of CPUs (2-32)"
> +	range 2 32
> +	depends on SMP
> +	default 8
> +	help
> +	  On multiprocessor machines, U-Boot sets up a stack for each CPU.
> +	  Stack memory is pre-allocated. U-Boot must therefore know the
> +	  maximum number of CPUs that may be present.
> +
>   endmenu
> diff --git a/arch/riscv/include/asm/global_data.h b/arch/riscv/include/asm/global_data.h
> index a3a342c6e1..80e3165e39 100644
> --- a/arch/riscv/include/asm/global_data.h
> +++ b/arch/riscv/include/asm/global_data.h
> @@ -10,12 +10,18 @@
>   #ifndef	__ASM_GBL_DATA_H
>   #define __ASM_GBL_DATA_H
>   
> +#include <asm/smp.h>
> +
>   /* Architecture-specific global data */
>   struct arch_global_data {
>   	long boot_hart;		/* boot hart id */
>   #ifdef CONFIG_SIFIVE_CLINT
>   	void __iomem *clint;	/* clint base address */
>   #endif
> +#ifdef CONFIG_SMP
> +	struct ipi_data ipi[CONFIG_NR_CPUS];
> +#endif
> +	ulong available_harts;
>   };
>   
>   #include <asm-generic/global_data.h>
> diff --git a/arch/riscv/include/asm/smp.h b/arch/riscv/include/asm/smp.h
> new file mode 100644
> index 0000000000..bc863fdbaf
> --- /dev/null
> +++ b/arch/riscv/include/asm/smp.h
> @@ -0,0 +1,53 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Copyright (C) 2019 Fraunhofer AISEC,
> + * Lukas Auer <lukas.auer@aisec.fraunhofer.de>
> + */
> +
> +#ifndef _ASM_RISCV_SMP_H
> +#define _ASM_RISCV_SMP_H
> +
> +/**
> + * struct ipi_data - Inter-processor interrupt (IPI) data structure
> + *
> + * IPIs are used for SMP support to communicate to other harts what function to
> + * call. Functions are in the form
> + * void (*addr)(ulong hart, ulong arg0, ulong arg1).
> + *
> + * The function address and the two arguments, arg0 and arg1, are stored in the
> + * IPI data structure. The hart ID is inserted by the hart handling the IPI and
> + * calling the function.
> + *
> + * @addr: Address of function
> + * @arg0: First argument of function
> + * @arg1: Second argument of function
> + */
> +struct ipi_data {
> +	ulong addr;
> +	ulong arg0;
> +	ulong arg1;
> +};
> +
> +/**
> + * handle_ipi() - interrupt handler for software interrupts
> + *
> + * The IPI interrupt handler must be called to handle software interrupts. It
> + * calls the function specified in the hart's IPI data structure.
> + *
> + * @hart: Hart ID of the current hart
> + */
> +void handle_ipi(ulong hart);
> +
> +/**
> + * smp_call_function() - Call a function on all other harts
> + *
> + * Send IPIs with the specified function call to all harts.
> + *
> + * @addr: Address of function
> + * @arg0: First argument of function
> + * @arg1: Second argument of function
> + * @return 0 if OK, -ve on error
> + */
> +int smp_call_function(ulong addr, ulong arg0, ulong arg1);
> +
> +#endif
> diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
> index edfa61690c..19370f9749 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -14,6 +14,7 @@ obj-$(CONFIG_SIFIVE_CLINT) += sifive_clint.o
>   obj-y	+= interrupts.o
>   obj-y	+= reset.o
>   obj-y   += setjmp.o
> +obj-$(CONFIG_SMP) += smp.o
>   
>   # For building EFI apps
>   CFLAGS_$(EFI_CRT0) := $(CFLAGS_EFI)
> diff --git a/arch/riscv/lib/smp.c b/arch/riscv/lib/smp.c
> new file mode 100644
> index 0000000000..edef8a687d
> --- /dev/null
> +++ b/arch/riscv/lib/smp.c
> @@ -0,0 +1,116 @@
> +// SPDX-License-Identifier: GPL-2.0+
> +/*
> + * Copyright (C) 2019 Fraunhofer AISEC,
> + * Lukas Auer <lukas.auer@aisec.fraunhofer.de>
> + */
> +
> +#include <common.h>
> +#include <dm.h>
> +#include <asm/barrier.h>
> +#include <asm/smp.h>
> +
> +DECLARE_GLOBAL_DATA_PTR;
> +
> +/**
> + * riscv_send_ipi() - Send inter-processor interrupt (IPI)
> + *
> + * Platform code must provide this function.
> + *
> + * @hart: Hart ID of receiving hart
> + * @return 0 if OK, -ve on error
> + */
> +extern int riscv_send_ipi(int hart);
> +
> +/**
> + * riscv_clear_ipi() - Clear inter-processor interrupt (IPI)
> + *
> + * Platform code must provide this function.
> + *
> + * @hart: Hart ID of hart to be cleared
> + * @return 0 if OK, -ve on error
> + */
> +extern int riscv_clear_ipi(int hart);
> +
> +static int send_ipi_many(struct ipi_data *ipi)
> +{
> +	ofnode node, cpus;
> +	u32 reg;
> +	int ret;
> +
> +	cpus = ofnode_path("/cpus");
> +	if (!ofnode_valid(cpus)) {
> +		pr_err("Can't find cpus node!\n");
> +		return -EINVAL;
> +	}
> +
> +	ofnode_for_each_subnode(node, cpus) {
> +		/* skip if hart is marked as not available in the device tree */
> +		if (!ofnode_is_available(node))
> +			continue;
> +
> +		/* read hart ID of CPU */
> +		ret = ofnode_read_u32(node, "reg", &reg);
> +		if (ret)
> +			continue;
> +
> +		/* skip if it is the hart we are running on */
> +		if (reg == gd->arch.boot_hart)
> +			continue;
> +
> +		if (reg >= CONFIG_NR_CPUS) {
> +			pr_err("Hart ID %d is out of range, increase CONFIG_NR_CPUS\n",
> +			       reg);
> +			continue
> +		}
> +
> +		/* skip if hart is not available */
> +		if (!(gd->arch.available_harts & (1 << reg)))
> +			continue;
> +
> +		gd->arch.ipi[reg].addr = ipi->addr;
> +		gd->arch.ipi[reg].arg0 = ipi->arg0;
> +		gd->arch.ipi[reg].arg1 = ipi->arg1;
> +
> +		ret = riscv_send_ipi(reg);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	return 0;
> +}
> +
> +void handle_ipi(ulong hart)
> +{
> +	int ret;
> +	void (*smp_function)(ulong hart, ulong arg0, ulong arg1);
> +
> +	if (hart >= CONFIG_NR_CPUS)
> +		return;
> +

A warning here may help.

> +	ret = riscv_clear_ipi(hart);
> +	if (ret) {
> +		pr_err("Cannot clear IPI\n");
> +		return;
> +	}
> +

Currently, sbi_clear_ipi() doesn't return anything and riscv_clear_ipi() 
is always returning 0. I guess you kept the check here so that we don't 
have make changes in future. But IMHO, we should add it if SBI spec is 
changed so that sbi_clear_ipi can return errors.

Regards,
Atish
> +	__smp_mb();
> +
> +	smp_function = (void (*)(ulong, ulong, ulong))gd->arch.ipi[hart].addr;
> +	invalidate_icache_all();
> +
> +	smp_function(hart, gd->arch.ipi[hart].arg0, gd->arch.ipi[hart].arg1);
> +}
> +
> +int smp_call_function(ulong addr, ulong arg0, ulong arg1)
> +{
> +	int ret = 0;
> +	struct ipi_data ipi;
> +
> +	ipi.addr = addr;
> +	ipi.arg0 = arg0;
> +	ipi.arg1 = arg1;
> +
> +	ret = send_ipi_many(&ipi);
> +
> +	return ret;
> +}
>