diff mbox

[v2,02/16] ARM: b.L: secondary kernel entry code

Message ID 1359008879-9015-3-git-send-email-nicolas.pitre@linaro.org (mailing list archive)
State New, archived
Headers show

Commit Message

Nicolas Pitre Jan. 24, 2013, 6:27 a.m. UTC 
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 <nico@linaro.org>
---
 arch/arm/Kconfig                |  6 +++
 arch/arm/common/Makefile        |  1 +
 arch/arm/common/bL_entry.c      | 29 +++++++++++++++
 arch/arm/common/bL_head.S       | 81 +++++++++++++++++++++++++++++++++++++++++
 arch/arm/include/asm/bL_entry.h | 35 ++++++++++++++++++
 5 files changed, 152 insertions(+)
 create mode 100644 arch/arm/common/bL_entry.c
 create mode 100644 arch/arm/common/bL_head.S
 create mode 100644 arch/arm/include/asm/bL_entry.h

Comments

Will Deacon Jan. 28, 2013, 2:46 p.m. UTC | #1 
Hi Nicolas,

On Thu, Jan 24, 2013 at 06:27:45AM +0000, 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.

What's your plan for this TODO? Do you aim to merge the code first and add
that later? If so, maybe add a TODO comment in the code as well?

> diff --git a/arch/arm/common/bL_entry.c b/arch/arm/common/bL_entry.c
> new file mode 100644
> index 0000000000..4e1044612d
> --- /dev/null
> +++ b/arch/arm/common/bL_entry.c
> @@ -0,0 +1,29 @@
> +/*
> + * arch/arm/common/bL_entry.c -- big.LITTLE kernel re-entry point
> + *
> + * Created by:  Nicolas Pitre, March 2012
> + * Copyright:   (C) 2012-2013  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/kernel.h>
> +#include <linux/init.h>
> +
> +#include <asm/bL_entry.h>

Similarly with the naming... was there any consensus to replace bL_ with
something else? I personally find the capitalisation pretty jarring and at
odds with the rest of the kernel, but "bl" is branch-and-link so that's also
not much better.

> diff --git a/arch/arm/include/asm/bL_entry.h b/arch/arm/include/asm/bL_entry.h
> new file mode 100644
> index 0000000000..7525614243
> --- /dev/null
> +++ b/arch/arm/include/asm/bL_entry.h
> @@ -0,0 +1,35 @@
> +/*
> + * arch/arm/include/asm/bL_entry.h
> + *
> + * Created by:  Nicolas Pitre, April 2012
> + * Copyright:   (C) 2012-2013  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.
> + */
> +
> +#ifndef BL_ENTRY_H
> +#define BL_ENTRY_H
> +
> +#define BL_MAX_CPUS_PER_CLUSTER	4
> +#define BL_MAX_CLUSTERS		2

Again, do you have any ideas/plans on how to remove these constant limits?

Cheers,

Will
Nicolas Pitre Jan. 28, 2013, 3:07 p.m. UTC | #2 
On Mon, 28 Jan 2013, Will Deacon wrote:

> Hi Nicolas,
> 
> On Thu, Jan 24, 2013 at 06:27:45AM +0000, 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.
> 
> What's your plan for this TODO? Do you aim to merge the code first and add
> that later? If so, maybe add a TODO comment in the code as well?

That should come later as this is probably going to be a non trivial 
task.  We might also decide that the current code is good enough for now 
and it is likely to be the case for a few years.

> > diff --git a/arch/arm/common/bL_entry.c b/arch/arm/common/bL_entry.c
> > new file mode 100644
> > index 0000000000..4e1044612d
> > --- /dev/null
> > +++ b/arch/arm/common/bL_entry.c
> > @@ -0,0 +1,29 @@
> > +/*
> > + * arch/arm/common/bL_entry.c -- big.LITTLE kernel re-entry point
> > + *
> > + * Created by:  Nicolas Pitre, March 2012
> > + * Copyright:   (C) 2012-2013  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/kernel.h>
> > +#include <linux/init.h>
> > +
> > +#include <asm/bL_entry.h>
> 
> Similarly with the naming... was there any consensus to replace bL_ with
> something else? I personally find the capitalisation pretty jarring and at
> odds with the rest of the kernel, but "bl" is branch-and-link so that's also
> not much better.

I really find the capitalisation incredibly nice and to the point.  
There is no better way to unambiguously refer to "big.LITTLE" with a 
2-letter prefix.

But as I said, the naming is something I want to change to make this 
code appear more generic as there is nothing really b.L specific here.  
That is a trivial change, once I'm settled on something.

> > diff --git a/arch/arm/include/asm/bL_entry.h b/arch/arm/include/asm/bL_entry.h
> > new file mode 100644
> > index 0000000000..7525614243
> > --- /dev/null
> > +++ b/arch/arm/include/asm/bL_entry.h
> > @@ -0,0 +1,35 @@
> > +/*
> > + * arch/arm/include/asm/bL_entry.h
> > + *
> > + * Created by:  Nicolas Pitre, April 2012
> > + * Copyright:   (C) 2012-2013  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.
> > + */
> > +
> > +#ifndef BL_ENTRY_H
> > +#define BL_ENTRY_H
> > +
> > +#define BL_MAX_CPUS_PER_CLUSTER	4
> > +#define BL_MAX_CLUSTERS		2
> 
> Again, do you have any ideas/plans on how to remove these constant limits?

Not for the initial merge.  Again, this should serve the systems to come 
in the next few years just fine.  That gives us plenty of time to 
enhance this code with proper dynamic allocation.


Nicolas
diff mbox

Patch

diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 67874b82a4..3dd5591c79 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -1584,6 +1584,12 @@  config HAVE_ARM_TWD
 	help
 	  This options enables support for the ARM timer and watchdog unit
 
+config BIG_LITTLE
+	bool "big.LITTLE support"
+	depends on CPU_V7 && SMP
+	help
+	  This option enables support for the big.LITTLE architecture.
+
 choice
 	prompt "Memory split"
 	default VMSPLIT_3G
diff --git a/arch/arm/common/Makefile b/arch/arm/common/Makefile
index e8a4e58f1b..8025899a20 100644
--- a/arch/arm/common/Makefile
+++ b/arch/arm/common/Makefile
@@ -13,3 +13,4 @@  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_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..4e1044612d
--- /dev/null
+++ b/arch/arm/common/bL_entry.c
@@ -0,0 +1,29 @@ 
+/*
+ * arch/arm/common/bL_entry.c -- big.LITTLE kernel re-entry point
+ *
+ * Created by:  Nicolas Pitre, March 2012
+ * Copyright:   (C) 2012-2013  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/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_MAX_CLUSTERS][BL_MAX_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;
+	__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]));
+}
diff --git a/arch/arm/common/bL_head.S b/arch/arm/common/bL_head.S
new file mode 100644
index 0000000000..072a13da20
--- /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) 2012-2013  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		@ MPIDR
+	ubfx	r9, r0, #0, #4			@ r9 = cpu
+	ubfx	r10, r0, #8, #4			@ r10 = cluster
+	mov	r3, #BL_MAX_CPUS_PER_CLUSTER
+	mla	r4, r3, r10, r9			@ r4 = canonical CPU index
+	cmp	r4, #(BL_MAX_CPUS_PER_CLUSTER * BL_MAX_CLUSTERS)
+	blo	2f
+
+	/* We didn't expect this CPU.  Try to cheaply make it quiet. */
+1:	wfi
+	wfe
+	b	1b
+
+2:	pr_dbg	r4, "kernel bL_entry_point\n"
+
+	/*
+	 * MMU is off so we need to get to bL_entry_vectors in a
+	 * position independent way.
+	 */
+	adr	r5, 3f
+	ldr	r6, [r5]
+	add	r6, r5, r6			@ r6 = bL_entry_vectors
+
+bL_entry_gated:
+	ldr	r5, [r6, r4, lsl #2]		@ r5 = CPU entry vector
+	cmp	r5, #0
+	wfeeq
+	beq	bL_entry_gated
+	pr_dbg	r4, "released\n"
+	bx	r5
+
+	.align	2
+
+3:	.word	bL_entry_vectors - .
+
+ENDPROC(bL_entry_point)
+
+	.bss
+	.align	5
+
+	.type	bL_entry_vectors, #object
+ENTRY(bL_entry_vectors)
+	.space	4 * BL_MAX_CLUSTERS * BL_MAX_CPUS_PER_CLUSTER
diff --git a/arch/arm/include/asm/bL_entry.h b/arch/arm/include/asm/bL_entry.h
new file mode 100644
index 0000000000..7525614243
--- /dev/null
+++ b/arch/arm/include/asm/bL_entry.h
@@ -0,0 +1,35 @@ 
+/*
+ * arch/arm/include/asm/bL_entry.h
+ *
+ * Created by:  Nicolas Pitre, April 2012
+ * Copyright:   (C) 2012-2013  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.
+ */
+
+#ifndef BL_ENTRY_H
+#define BL_ENTRY_H
+
+#define BL_MAX_CPUS_PER_CLUSTER	4
+#define BL_MAX_CLUSTERS		2
+
+#ifndef __ASSEMBLY__
+
+/*
+ * Platform specific code should use this symbol to set up secondary
+ * entry location for processors to use when released from reset.
+ */
+extern void bL_entry_point(void);
+
+/*
+ * This is used to indicate where the given CPU from given cluster should
+ * branch once it is ready to re-enter the kernel using ptr, or NULL if it
+ * should be gated.  A gated CPU is held in a WFE loop until its vector
+ * becomes non NULL.
+ */
+void bL_set_entry_vector(unsigned cpu, unsigned cluster, void *ptr);
+
+#endif /* ! __ASSEMBLY__ */
+#endif