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

[Auer, Lukas <lukas.auer@aisec.fraunhofer.de>]

On Wed, 2019-03-06 at 19:20 -0800, Atish Patra wrote:
> 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.
> 

This is meant more as a sanity check. Harts with an ID greater than
CONFIG_NR_CPUS should never run handle_ipi().
Warnings are already printed by the hart sending the IPIs, in
send_ipi_many() called by smp_call_function().

> > +	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.
> 

The check is required if U-Boot is running in machine mode. The IPI
implementation using the CLINT driver returns an error if it cannot get
the memory address of the CLINT device.

I just noticed that no error is printed if riscv_send_ipi() returns an
error in send_ipi_many(). I will add one in the next version.

Thanks,
Lukas

> 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;
> > +}
> >