Subject: [PATCH 01/16] ARM: b.L: secondary kernel entry code

From: [email-masked] (Santosh Shilimkar)
Date: Fri, 11 Jan 2013 22:46:07 +0530

On Thursday 10 January 2013 05:50 AM, Nicolas Pitre wrote:
> CPUs in a big.LITTLE systems have special needs when entering the kernel
> due to a hotplug event, or when resuming from a deep sleep mode.
>
> This is vectorized so multiple CPUs can enter the kernel in parallel
> without serialization.
>
> Only the basic structure is introduced here.  This will be extended
> later.
>
> TODO: MPIDR based indexing should eventually be made runtime adjusted.
>
> Signed-off-by: Nicolas Pitre <[email-masked]>
> ---

[..]

> diff --git a/arch/arm/common/Makefile b/arch/arm/common/Makefile
> index e8a4e58f1b..50880c494f 100644
> --- a/arch/arm/common/Makefile
> +++ b/arch/arm/common/Makefile
> @@ -13,3 +13,6 @@ obj-$(CONFIG_SHARP_PARAM)	+= sharpsl_param.o
>   obj-$(CONFIG_SHARP_SCOOP)	+= scoop.o
>   obj-$(CONFIG_PCI_HOST_ITE8152)  += it8152.o
>   obj-$(CONFIG_ARM_TIMER_SP804)	+= timer-sp.o
> +obj-$(CONFIG_FIQ_GLUE)		+= fiq_glue.o fiq_glue_setup.o
> +obj-$(CONFIG_FIQ_DEBUGGER)	+= fiq_debugger.o
> +obj-$(CONFIG_BIG_LITTLE)	+= bL_head.o bL_entry.o
> diff --git a/arch/arm/common/bL_entry.c b/arch/arm/common/bL_entry.c
> new file mode 100644
> index 0000000000..80fff49417
> --- /dev/null
> +++ b/arch/arm/common/bL_entry.c
> @@ -0,0 +1,30 @@
> +/*
> + * arch/arm/common/bL_entry.c -- big.LITTLE kernel re-entry point
> + *
> + * Created by:  Nicolas Pitre, March 2012
> + * Copyright:   (C) 2012  Linaro Limited
2013 now :-)
Looks like you need to update rest of the patches as well.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/kernel.h>
> +#include <linux/init.h>
> +
> +#include <asm/bL_entry.h>
> +#include <asm/barrier.h>
> +#include <asm/proc-fns.h>
> +#include <asm/cacheflush.h>
> +
> +extern volatile unsigned long bL_entry_vectors[BL_NR_CLUSTERS][BL_CPUS_PER_CLUSTER];
> +
> +void bL_set_entry_vector(unsigned cpu, unsigned cluster, void *ptr)
> +{
> +	unsigned long val = ptr ? virt_to_phys(ptr) : 0;
> +	bL_entry_vectors[cluster][cpu] = val;
> +	smp_wmb();
> +	__cpuc_flush_dcache_area((void *)&bL_entry_vectors[cluster][cpu], 4);
> +	outer_clean_range(__pa(&bL_entry_vectors[cluster][cpu]),
> +			  __pa(&bL_entry_vectors[cluster][cpu + 1]));
> +}
I had the same question about smp_wmb() as Catalin but after following
rest of the comments, I understand it will be removed so thats good.

> diff --git a/arch/arm/common/bL_head.S b/arch/arm/common/bL_head.S
> new file mode 100644
> index 0000000000..9d351f2b4c
> --- /dev/null
> +++ b/arch/arm/common/bL_head.S
> @@ -0,0 +1,81 @@
> +/*
> + * arch/arm/common/bL_head.S -- big.LITTLE kernel re-entry point
> + *
> + * Created by:  Nicolas Pitre, March 2012
> + * Copyright:   (C) 2012  Linaro Limited
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +
> +#include <linux/linkage.h>
> +#include <asm/bL_entry.h>
> +
> +	.macro	pr_dbg	cpu, string
> +#if defined(CONFIG_DEBUG_LL) && defined(DEBUG)
> +	b	1901f
> +1902:	.ascii	"CPU 0: \0CPU 1: \0CPU 2: \0CPU 3: \0"
> +	.ascii	"CPU 4: \0CPU 5: \0CPU 6: \0CPU 7: \0"
> +1903:	.asciz	"\string"
> +	.align
> +1901:	adr	r0, 1902b
> +	add	r0, r0, \cpu, lsl #3
> +	bl	printascii
> +	adr	r0, 1903b
> +	bl	printascii
> +#endif
> +	.endm
> +
> +	.arm
> +	.align
> +
> +ENTRY(bL_entry_point)
> +
> + THUMB(	adr	r12, BSYM(1f)	)
> + THUMB(	bx	r12		)
> + THUMB(	.thumb			)
> +1:
> +	mrc	p15, 0, r0, c0, c0, 5
> +	ubfx	r9, r0, #0, #4			@ r9 = cpu
> +	ubfx	r10, r0, #8, #4			@ r10 = cluster
> +	mov	r3, #BL_CPUS_PER_CLUSTER
> +	mla	r4, r3, r10, r9			@ r4 = canonical CPU index
> +	cmp	r4, #(BL_CPUS_PER_CLUSTER * BL_NR_CLUSTERS)
> +	blo	2f
> +
> +	/* We didn't expect this CPU.  Try to make it quiet. */
> +1:	wfi
> +	wfe

Why do you need a wfe followed by wif ?
Just curious.

Regards
Santosh