Re: [PATCH 3/3] ARM: BCM: Add SMP support for Broadcom NSP

[Hauke Mehrtens <hauke-5/S+JYg5SzeELgA04lAiVw@public.gmane.org>]

On 10/14/2015 07:47 PM, Kapil Hali wrote:
> Add SMP support for Broadcom's Northstar Plus SoC,
> cpu enable method and pen_release procedures. This
> changes also consolidates iProc family's - BCM NSP
> and BCM Kona, SMP handling in a common file.

This will probably also work on normal Northstar CPUs without changes.

> Northstar Plus SoC is based on ARM Cortex-A9
> revision r3p0 which requires configuration for ARM
> Errata 764369 for SMP. This change adds the needed
> configuration option.
> 
> Signed-off-by: Kapil Hali <kapilh-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
> ---
>  arch/arm/mach-bcm/Kconfig                   |   2 +
>  arch/arm/mach-bcm/Makefile                  |   8 +-
>  arch/arm/mach-bcm/bcm_nsp.h                 |  19 ++++
>  arch/arm/mach-bcm/headsmp.S                 |  37 ++++++++
>  arch/arm/mach-bcm/{kona_smp.c => platsmp.c} | 142 ++++++++++++++++++++++++++--
>  5 files changed, 197 insertions(+), 11 deletions(-)
>  create mode 100644 arch/arm/mach-bcm/bcm_nsp.h
>  create mode 100644 arch/arm/mach-bcm/headsmp.S
>  rename arch/arm/mach-bcm/{kona_smp.c => platsmp.c} (63%)
> 
> diff --git a/arch/arm/mach-bcm/Kconfig b/arch/arm/mach-bcm/Kconfig
> index 1679fa4..2e9dbb5 100644
> --- a/arch/arm/mach-bcm/Kconfig
> +++ b/arch/arm/mach-bcm/Kconfig
> @@ -40,6 +40,8 @@ config ARCH_BCM_NSP
>  	select ARCH_BCM_IPROC
>  	select ARM_ERRATA_754322
>  	select ARM_ERRATA_775420
> +	select ARM_ERRATA_764369 if SMP
> +	select HAVE_SMP
>  	help
>  	  Support for Broadcom Northstar Plus SoC.
>  	  Broadcom Northstar Plus family of SoCs are used for switching control
> diff --git a/arch/arm/mach-bcm/Makefile b/arch/arm/mach-bcm/Makefile
> index 892261f..36a4ca30 100644
> --- a/arch/arm/mach-bcm/Makefile
> +++ b/arch/arm/mach-bcm/Makefile
> @@ -14,7 +14,11 @@
>  obj-$(CONFIG_ARCH_BCM_CYGNUS) +=  bcm_cygnus.o
>  
>  # Northstar Plus
> -obj-$(CONFIG_ARCH_BCM_NSP) += bcm_nsp.o
> +obj-$(CONFIG_ARCH_BCM_NSP)	+= bcm_nsp.o
> +
> +ifeq ($(CONFIG_ARCH_BCM_NSP),y)
> +obj-$(CONFIG_SMP)		+= headsmp.o platsmp.o
> +endif
>  
>  # BCM281XX
>  obj-$(CONFIG_ARCH_BCM_281XX)	+= board_bcm281xx.o
> @@ -23,7 +27,7 @@ obj-$(CONFIG_ARCH_BCM_281XX)	+= board_bcm281xx.o
>  obj-$(CONFIG_ARCH_BCM_21664)	+= board_bcm21664.o
>  
>  # BCM281XX and BCM21664 SMP support
> -obj-$(CONFIG_ARCH_BCM_MOBILE_SMP) += kona_smp.o
> +obj-$(CONFIG_ARCH_BCM_MOBILE_SMP) += platsmp.o
>  
>  # BCM281XX and BCM21664 L2 cache control
>  obj-$(CONFIG_ARCH_BCM_MOBILE_L2_CACHE) += kona_l2_cache.o
> diff --git a/arch/arm/mach-bcm/bcm_nsp.h b/arch/arm/mach-bcm/bcm_nsp.h
> new file mode 100644
> index 0000000..58e1e80
> --- /dev/null
> +++ b/arch/arm/mach-bcm/bcm_nsp.h
> @@ -0,0 +1,19 @@
> +/*
> + * Copyright (C) 2015 Broadcom Corporation
> + *
> + * 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 version 2.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#ifndef __BCM_NSP_H
> +#define __BCM_NSP_H
> +
> +extern void nsp_secondary_startup(void);
> +
> +#endif /* __BCM_NSP_H */
> diff --git a/arch/arm/mach-bcm/headsmp.S b/arch/arm/mach-bcm/headsmp.S
> new file mode 100644
> index 0000000..0da13b2
> --- /dev/null
> +++ b/arch/arm/mach-bcm/headsmp.S
> @@ -0,0 +1,37 @@
> +/*
> + * Copyright (C) 2015 Broadcom Corporation
> + *
> + * 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 version 2.
> + *
> + * This program is distributed "as is" WITHOUT ANY WARRANTY of any
> + * kind, whether express or implied; without even the implied warranty
> + * of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> + * GNU General Public License for more details.
> + */
> +
> +#include <linux/linkage.h>
> +
> +/*
> + * iProc specific entry point for secondary CPUs.  This provides
> + * a "holding pen" into which all secondary cores are held until
> + * we are ready for them to initialise.
> + */
> +ENTRY(nsp_secondary_startup)
> +	mrc     p15, 0, r0, c0, c0, 5
> +	and     r0, r0, #15
> +	adr     r4, 1f
> +	ldmia   r4, {r5, r6}
> +	sub     r4, r4, r5
> +	add     r6, r6, r4
> +pen:	ldr     r7, [r6]
> +	cmp     r7, r0
> +	bne     pen
> +
> +	b    secondary_startup
> +
> +1:	.long   .
> +	.long   pen_release
> +
> +ENDPROC(nsp_secondary_startup)
> diff --git a/arch/arm/mach-bcm/kona_smp.c b/arch/arm/mach-bcm/platsmp.c
> similarity index 63%
> rename from arch/arm/mach-bcm/kona_smp.c
> rename to arch/arm/mach-bcm/platsmp.c
> index 66a0465..619030e 100644
> --- a/arch/arm/mach-bcm/kona_smp.c
> +++ b/arch/arm/mach-bcm/platsmp.c
> @@ -1,5 +1,5 @@
>  /*
> - * Copyright (C) 2014 Broadcom Corporation
> + * Copyright (C) 2014-2015 Broadcom Corporation
>   * Copyright 2014 Linaro Limited
>   *
>   * This program is free software; you can redistribute it and/or
> @@ -12,16 +12,23 @@
>   * GNU General Public License for more details.
>   */
>  
> -#include <linux/init.h>
> +#include <linux/cpumask.h>
> +#include <linux/delay.h>
>  #include <linux/errno.h>
> +#include <linux/init.h>
>  #include <linux/io.h>
> +#include <linux/jiffies.h>
>  #include <linux/of.h>
>  #include <linux/sched.h>
> +#include <linux/smp.h>
>  
> +#include <asm/cacheflush.h>
>  #include <asm/smp.h>
>  #include <asm/smp_plat.h>
>  #include <asm/smp_scu.h>
>  
> +#include "bcm_nsp.h"
> +
>  /* Size of mapped Cortex A9 SCU address space */
>  #define CORTEX_A9_SCU_SIZE	0x58
>  
> @@ -34,6 +41,24 @@
>  /* I/O address of register used to coordinate secondary core startup */
>  static u32	secondary_boot;
>  
> +static DEFINE_SPINLOCK(boot_lock);
> +
> +/*
> + * Write pen_release in a way that is guaranteed to be visible to all
> + * observers, irrespective of whether they're taking part in coherency
> + * or not.  This is necessary for the hotplug code to work reliably.
> + */
> +static void write_pen_release(int val)
> +{
> +	pen_release = val;
> +	/*
> +	 * Ensure write to pen_release is visible to the other cores,
> +	 * here - primary core
> +	 */
> +	smp_wmb();
> +	sync_cache_w(&pen_release);
> +}
> +
>  /*
>   * Enable the Cortex A9 Snoop Control Unit
>   *
> @@ -75,6 +100,51 @@ static int __init scu_a9_enable(void)
>  	return 0;
>  }
>  
> +static int nsp_write_lut(void (*secondary_startup) (void))
> +{
> +	void __iomem *sku_rom_lut;
> +	phys_addr_t secondary_startup_phy;
> +
> +	if (!secondary_boot) {
> +		pr_warn("required secondary boot register not specified\n");
> +		return -EINVAL;
> +	}
> +
> +	sku_rom_lut = ioremap_nocache((phys_addr_t)secondary_boot,
> +						sizeof(secondary_boot));
> +	if (!sku_rom_lut) {
> +		pr_warn("unable to ioremap SKU-ROM LUT register\n");
> +		return -ENOMEM;
> +	}
> +
> +	secondary_startup_phy = virt_to_phys(secondary_startup);
> +	BUG_ON(secondary_startup_phy > (phys_addr_t)U32_MAX);
> +
> +	writel_relaxed(secondary_startup_phy, sku_rom_lut);
> +	/*
> +	 * Ensure the write is visible to the secondary core.
> +	 */
> +	smp_wmb();
> +
> +	iounmap(sku_rom_lut);
> +
> +	return 0;
> +}
> +
> +static void nsp_secondary_init(unsigned int cpu)
> +{
> +	/*
> +	 * Let the primary cpu know we are out of holding pen.
> +	 */
> +	write_pen_release(-1);
> +
> +	/*
> +	 * Synchronise with the boot thread.
> +	 */
> +	spin_lock(&boot_lock);
> +	spin_unlock(&boot_lock);
> +}
> +
>  static void __init bcm_smp_prepare_cpus(unsigned int max_cpus)
>  {
>  	static cpumask_t only_cpu_0 = { CPU_BITS_CPU0 };
> @@ -95,11 +165,11 @@ static void __init bcm_smp_prepare_cpus(unsigned int max_cpus)
>  	/*
>  	 * Our secondary enable method requires a "secondary-boot-reg"
>  	 * property to specify a register address used to request the
> -	 * ROM code boot a secondary code.  If we have any trouble
> +	 * ROM code boot a secondary core.  If we have any trouble
>  	 * getting this we fall back to uniprocessor mode.
>  	 */
>  	if (of_property_read_u32(node, OF_SECONDARY_BOOT, &secondary_boot)) {
> -		pr_err("%s: missing/invalid " OF_SECONDARY_BOOT " property\n",
> +		pr_warn("%s: missing/invalid " OF_SECONDARY_BOOT " property\n",
>  			node->name);
>  		ret = -ENOENT;		/* Arrange to disable SMP */
>  		goto out;
> @@ -115,7 +185,6 @@ out:
>  	of_node_put(node);
>  	if (ret) {
>  		/* Update the CPU present map to reflect uniprocessor mode */
> -		BUG_ON(ret != -ENOENT);
>  		pr_warn("disabling SMP\n");
>  		init_cpu_present(&only_cpu_0);
>  	}
> @@ -139,7 +208,7 @@ out:
>   * - Wait for the secondary boot register to be re-written, which
>   *   indicates the secondary core has started.
>   */
> -static int bcm_boot_secondary(unsigned int cpu, struct task_struct *idle)
> +static int kona_boot_secondary(unsigned int cpu, struct task_struct *idle)
>  {
>  	void __iomem *boot_reg;
>  	phys_addr_t boot_func;
> @@ -162,7 +231,7 @@ static int bcm_boot_secondary(unsigned int cpu, struct task_struct *idle)
>  	boot_reg = ioremap_nocache((phys_addr_t)secondary_boot, sizeof(u32));
>  	if (!boot_reg) {
>  		pr_err("unable to map boot register for cpu %u\n", cpu_id);
> -		return -ENOSYS;
> +		return -ENOMEM;
>  	}
>  
>  	/*
> @@ -191,12 +260,67 @@ static int bcm_boot_secondary(unsigned int cpu, struct task_struct *idle)
>  
>  	pr_err("timeout waiting for cpu %u to start\n", cpu_id);
>  
> -	return -ENOSYS;
> +	return -ENXIO;
> +}
> +
> +static int nsp_boot_secondary(unsigned int cpu, struct task_struct *idle)
> +{
> +	unsigned long timeout;
> +	int ret;
> +
> +	/*
> +	 * After wake up, secondary core branches to the startup
> +	 * address programmed at SKU ROM LUT location.
> +	 */
> +	ret = nsp_write_lut(nsp_secondary_startup);
> +	if (ret) {
> +		pr_err("unable to write startup addr to SKU ROM LUT\n");
> +		goto out;
> +	}
> +
> +	/*
> +	 * The secondary processor is waiting to be released from
> +	 * the holding pen - release it, then wait for it to flag
> +	 * that it has been released by resetting pen_release.
> +	 */
> +	spin_lock(&boot_lock);
> +
> +	write_pen_release(cpu_logical_map(cpu));
> +	/*
> +	 * Send an Event to wake up the secondary core which is in
> +	 * WFE state. Updated pen_release should also be visible to
> +	 * the secondary core.
> +	 */
> +	dsb_sev();
> +
> +	timeout = jiffies + (1 * HZ);
> +	while (time_before(jiffies, timeout)) {
> +		/* Make sure loads on other CPU is visible */
> +		smp_rmb();
> +		if (pen_release == -1)
> +			break;
> +
> +		udelay(10);
> +	}
> +
> +	spin_unlock(&boot_lock);

Why is this boot_lock needed? As far as I understand it asserts that
both CPUs leave nsp_boot_secondary() and nsp_secondary_init() at the
same time.

> +
> +	ret = pen_release != -1 ? -ENXIO : 0;
> +
> +out:
> +	return ret;
>  }
>  
>  static struct smp_operations bcm_smp_ops __initdata = {
>  	.smp_prepare_cpus	= bcm_smp_prepare_cpus,
> -	.smp_boot_secondary	= bcm_boot_secondary,
> +	.smp_boot_secondary	= kona_boot_secondary,
>  };
>  CPU_METHOD_OF_DECLARE(bcm_smp_bcm281xx, "brcm,bcm11351-cpu-method",
>  			&bcm_smp_ops);
> +
> +struct smp_operations nsp_smp_ops __initdata = {
> +	.smp_prepare_cpus	= bcm_smp_prepare_cpus,
> +	.smp_secondary_init	= nsp_secondary_init,
> +	.smp_boot_secondary	= nsp_boot_secondary,
> +};
> +CPU_METHOD_OF_DECLARE(bcm_smp_nsp, "brcm,bcm-nsp-smp", &nsp_smp_ops);
> 

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