Date:   Fri, 12 Oct 2018 12:09:52 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Guo Ren <ren_guo@...ky.com>, akpm@...ux-foundation.org,
        arnd@...db.de, daniel.lezcano@...aro.org, davem@...emloft.net,
        gregkh@...uxfoundation.org, hch@...radead.org,
        mark.rutland@....com, peterz@...radead.org, robh@...nel.org,
        tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        devicetree@...r.kernel.org, robh+dt@...nel.org,
        c-sky_gcc_upstream@...ky.com
Subject: Re: [PATCH V8 16/21] csky: SMP support

On 12/10/18 05:42, Guo Ren wrote:
> This patch adds boot, ipi, hotplug code for SMP.
> 
> Changelog:
>  - remove set_ipi_irq_mapping callback.
>  - Convert the cpumask to an interrupt-controller specific representation
>    in driver's code, and not the SMP code's.
>  - csky: remove irq_mapping from smp.c
>    There are some feedbacks from irqchip, and we need to adjust
>    "smp.c & smp.h" to match the csky_mp_intc modification.
>  - Move IPI_IRQ define into drivers/irqchip/csky_mpintc.c, because it's a
>    interrupt controller specific.
>  - Bugfix request_irq with IPI_IRQ, we must use irq_mapping return value
>    not directly use IPI_IRQ. The modification also involves csky_mp_intc.
> 
> Signed-off-by: Guo Ren <ren_guo@...ky.com>
> Cc: Marc Zyngier <marc.zyngier@....com>
> Cc: Mark Rutland <mark.rutland@....com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> ---
>  arch/csky/include/asm/smp.h |  28 ++++++
>  arch/csky/kernel/smp.c      | 237 ++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 265 insertions(+)
>  create mode 100644 arch/csky/include/asm/smp.h
>  create mode 100644 arch/csky/kernel/smp.c
> 
> diff --git a/arch/csky/include/asm/smp.h b/arch/csky/include/asm/smp.h
> new file mode 100644
> index 0000000..31f7b94
> --- /dev/null
> +++ b/arch/csky/include/asm/smp.h
> @@ -0,0 +1,28 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +
> +#ifndef __ASM_CSKY_SMP_H
> +#define __ASM_CSKY_SMP_H
> +
> +#include <linux/cpumask.h>
> +#include <linux/irqreturn.h>
> +#include <linux/threads.h>
> +
> +#ifdef CONFIG_SMP
> +
> +void __init setup_smp(void);
> +
> +void __init setup_smp_ipi(void);
> +
> +void __init enable_smp_ipi(void);
> +
> +void arch_send_call_function_ipi_mask(struct cpumask *mask);
> +
> +void arch_send_call_function_single_ipi(int cpu);
> +
> +void __init set_send_ipi(void (*func)(const struct cpumask *mask), int irq);
> +
> +#define raw_smp_processor_id()	(current_thread_info()->cpu)
> +
> +#endif /* CONFIG_SMP */
> +
> +#endif /* __ASM_CSKY_SMP_H */
> diff --git a/arch/csky/kernel/smp.c b/arch/csky/kernel/smp.c
> new file mode 100644
> index 0000000..5ea9516
> --- /dev/null
> +++ b/arch/csky/kernel/smp.c
> @@ -0,0 +1,237 @@
> +// SPDX-License-Identifier: GPL-2.0
> +
> +#include <linux/module.h>
> +#include <linux/init.h>
> +#include <linux/kernel.h>
> +#include <linux/mm.h>
> +#include <linux/sched.h>
> +#include <linux/kernel_stat.h>
> +#include <linux/notifier.h>
> +#include <linux/cpu.h>
> +#include <linux/percpu.h>
> +#include <linux/delay.h>
> +#include <linux/err.h>
> +#include <linux/irq.h>
> +#include <linux/irqdomain.h>
> +#include <linux/of.h>
> +#include <linux/sched/task_stack.h>
> +#include <linux/sched/mm.h>
> +#include <asm/irq.h>
> +#include <asm/traps.h>
> +#include <asm/sections.h>
> +#include <asm/mmu_context.h>
> +#include <asm/pgalloc.h>
> +
> +static struct {
> +	unsigned long bits ____cacheline_aligned;
> +} ipi_data[NR_CPUS] __cacheline_aligned;

Why isn't this a per-cpu variable?

> +
> +enum ipi_message_type {
> +	IPI_EMPTY,
> +	IPI_RESCHEDULE,
> +	IPI_CALL_FUNC,
> +	IPI_MAX
> +};
> +
> +static irqreturn_t handle_ipi(int irq, void *dev)
> +{
> +	unsigned long *pending_ipis = &ipi_data[smp_processor_id()].bits;
> +
> +	while (true) {
> +		unsigned long ops;
> +
> +		ops = xchg(pending_ipis, 0);
> +		if (ops == 0)
> +			return IRQ_HANDLED;
> +
> +		if (ops & (1 << IPI_RESCHEDULE))
> +			scheduler_ipi();
> +
> +		if (ops & (1 << IPI_CALL_FUNC))
> +			generic_smp_call_function_interrupt();
> +
> +		BUG_ON((ops >> IPI_MAX) != 0);
> +	}
> +
> +	return IRQ_HANDLED;
> +}
> +
> +static void (*send_arch_ipi)(const struct cpumask *mask);
> +
> +static int ipi_irq;
> +void __init set_send_ipi(void (*func)(const struct cpumask *mask), int irq)
> +{
> +	if (send_arch_ipi)
> +		return;
> +
> +	send_arch_ipi = func;
> +	ipi_irq = irq;
> +}
> +
> +static void
> +send_ipi_message(const struct cpumask *to_whom, enum ipi_message_type operation)
> +{
> +	int i;
> +
> +	for_each_cpu(i, to_whom)
> +		set_bit(operation, &ipi_data[i].bits);
> +
> +	smp_mb();
> +	send_arch_ipi(to_whom);
> +}
> +
> +void arch_send_call_function_ipi_mask(struct cpumask *mask)
> +{
> +	send_ipi_message(mask, IPI_CALL_FUNC);
> +}
> +
> +void arch_send_call_function_single_ipi(int cpu)
> +{
> +	send_ipi_message(cpumask_of(cpu), IPI_CALL_FUNC);
> +}
> +
> +static void ipi_stop(void *unused)
> +{
> +	while (1);
> +}
> +
> +void smp_send_stop(void)
> +{
> +	on_each_cpu(ipi_stop, NULL, 1);
> +}
> +
> +void smp_send_reschedule(int cpu)
> +{
> +	send_ipi_message(cpumask_of(cpu), IPI_RESCHEDULE);
> +}
> +
> +void *__cpu_up_stack_pointer[NR_CPUS];
> +void *__cpu_up_task_pointer[NR_CPUS];

Why aren't these per-cpu variables? More importantly, what are they used
for? None of the patches in this series are using them.

> +
> +void __init smp_prepare_boot_cpu(void)
> +{
> +}
> +
> +void __init smp_prepare_cpus(unsigned int max_cpus)
> +{
> +}
> +
> +void __init enable_smp_ipi(void)
> +{
> +	enable_percpu_irq(ipi_irq, 0);
> +}

Why isn't this function static?

> +
> +static int ipi_dummy_dev;
> +void __init setup_smp_ipi(void)
> +{
> +	int rc;
> +
> +	if (ipi_irq == 0)
> +		panic("%s IRQ mapping failed\n", __func__);
> +
> +	rc = request_percpu_irq(ipi_irq, handle_ipi, "IPI Interrupt",
> +				&ipi_dummy_dev);
> +	if (rc)
> +		panic("%s IRQ request failed\n", __func__);
> +
> +	enable_smp_ipi();
> +}
> +
> +void __init setup_smp(void)
> +{
> +	struct device_node *node = NULL;
> +	int cpu;
> +
> +	while ((node = of_find_node_by_type(node, "cpu"))) {
> +		if (!of_device_is_available(node))
> +			continue;
> +
> +		if (of_property_read_u32(node, "reg", &cpu))
> +			continue;
> +
> +		if (cpu >= NR_CPUS)
> +			continue;
> +
> +		set_cpu_possible(cpu, true);
> +		set_cpu_present(cpu, true);
> +	}
> +}
> +
> +extern void _start_smp_secondary(void);
> +
> +volatile unsigned int secondary_hint;
> +volatile unsigned int secondary_ccr;
> +volatile unsigned int secondary_stack;

This looks pretty dodgy. Shouldn't you be using READ_ONCE/WRITE_ONCE
instead?

> +
> +int __cpu_up(unsigned int cpu, struct task_struct *tidle)
> +{
> +	unsigned int tmp;
> +
> +	secondary_stack = (unsigned int)tidle->stack + THREAD_SIZE;
> +
> +	secondary_hint = mfcr("cr31");
> +
> +	secondary_ccr  = mfcr("cr18");> +
> +	/* Flush dcache */
> +	mtcr("cr17", 0x22);
> +
> +	/* Enable cpu in SMP reset ctrl reg */
> +	tmp = mfcr("cr<29, 0>");
> +	tmp |= 1 << cpu;
> +	mtcr("cr<29, 0>", tmp);
> +
> +	/* Wait for the cpu online */
> +	while (!cpu_online(cpu));
> +
> +	secondary_stack = 0;
> +
> +	return 0;
> +}
> +
> +void __init smp_cpus_done(unsigned int max_cpus)
> +{
> +}
> +
> +int setup_profiling_timer(unsigned int multiplier)
> +{
> +	return -EINVAL;
> +}
> +
> +void csky_start_secondary(void)
> +{
> +	struct mm_struct *mm = &init_mm;
> +	unsigned int cpu = smp_processor_id();
> +
> +	mtcr("cr31", secondary_hint);
> +	mtcr("cr18", secondary_ccr);
> +
> +	mtcr("vbr", vec_base);
> +
> +	flush_tlb_all();
> +	write_mmu_pagemask(0);
> +	TLBMISS_HANDLER_SETUP_PGD(swapper_pg_dir);
> +	TLBMISS_HANDLER_SETUP_PGD_KERNEL(swapper_pg_dir);
> +
> +	asid_cache(smp_processor_id()) = ASID_FIRST_VERSION;
> +
> +#ifdef CONFIG_CPU_HAS_FPU
> +	init_fpu();
> +#endif
> +
> +	enable_smp_ipi();
> +
> +	mmget(mm);
> +	mmgrab(mm);
> +	current->active_mm = mm;
> +	cpumask_set_cpu(cpu, mm_cpumask(mm));
> +
> +	notify_cpu_starting(cpu);
> +	set_cpu_online(cpu, true);
> +
> +	pr_info("CPU%u Online: %s...\n", cpu, __func__);
> +
> +	local_irq_enable();
> +	preempt_disable();
> +	cpu_startup_entry(CPUHP_AP_ONLINE_IDLE);
> +}
> 

Thanks,

	M.
-- 
Jazz is not dead. It just smells funny...

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