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linux/arch/arm/kernel/sleep.S
Lorenzo Pieralisi 7604537bbb ARM: kernel: implement stack pointer save array through MPIDR hashing 
Current implementation of cpu_{suspend}/cpu_{resume} relies on the MPIDR
to index the array of pointers where the context is saved and restored.
The current approach works as long as the MPIDR can be considered a
linear index, so that the pointers array can simply be dereferenced by
using the MPIDR[7:0] value.
On ARM multi-cluster systems, where the MPIDR may not be a linear index,
to properly dereference the stack pointer array, a mapping function should
be applied to it so that it can be used for arrays look-ups.

This patch adds code in the cpu_{suspend}/cpu_{resume} implementation
that relies on shifting and ORing hashing method to map a MPIDR value to a
set of buckets precomputed at boot to have a collision free mapping from
MPIDR to context pointers.

The hashing algorithm must be simple, fast, and implementable with few
instructions since in the cpu_resume path the mapping is carried out with
the MMU off and the I-cache off, hence code and data are fetched from DRAM
with no-caching available. Simplicity is counterbalanced with a little
increase of memory (allocated dynamically) for stack pointers buckets, that
should be anyway fairly limited on most systems.

Memory for context pointers is allocated in a early_initcall with
size precomputed and stashed previously in kernel data structures.
Memory for context pointers is allocated through kmalloc; this
guarantees contiguous physical addresses for the allocated memory which
is fundamental to the correct functioning of the resume mechanism that
relies on the context pointer array to be a chunk of contiguous physical
memory. Virtual to physical address conversion for the context pointer
array base is carried out at boot to avoid fiddling with virt_to_phys
conversions in the cpu_resume path which is quite fragile and should be
optimized to execute as few instructions as possible.
Virtual and physical context pointer base array addresses are stashed in a
struct that is accessible from assembly using values generated through the
asm-offsets.c mechanism.

Cc: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Colin Cross <ccross@android.com>
Cc: Santosh Shilimkar <santosh.shilimkar@ti.com>
Cc: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Amit Kucheria <amit.kucheria@linaro.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Reviewed-by: Nicolas Pitre <nico@linaro.org>
Tested-by: Shawn Guo <shawn.guo@linaro.org>
Tested-by: Kevin Hilman <khilman@linaro.org>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
2013-06-20 11:24:11 +01:00

166 lines
4.8 KiB
ArmAsm
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#include <linux/linkage.h>
#include <linux/threads.h>
#include <asm/asm-offsets.h>
#include <asm/assembler.h>
#include <asm/glue-cache.h>
#include <asm/glue-proc.h>
.text
/*
* Implementation of MPIDR hash algorithm through shifting
* and OR'ing.
*
* @dst: register containing hash result
* @rs0: register containing affinity level 0 bit shift
* @rs1: register containing affinity level 1 bit shift
* @rs2: register containing affinity level 2 bit shift
* @mpidr: register containing MPIDR value
* @mask: register containing MPIDR mask
*
* Pseudo C-code:
*
*u32 dst;
*
*compute_mpidr_hash(u32 rs0, u32 rs1, u32 rs2, u32 mpidr, u32 mask) {
* u32 aff0, aff1, aff2;
* u32 mpidr_masked = mpidr & mask;
* aff0 = mpidr_masked & 0xff;
* aff1 = mpidr_masked & 0xff00;
* aff2 = mpidr_masked & 0xff0000;
* dst = (aff0 >> rs0 | aff1 >> rs1 | aff2 >> rs2);
*}
* Input registers: rs0, rs1, rs2, mpidr, mask
* Output register: dst
* Note: input and output registers must be disjoint register sets
(eg: a macro instance with mpidr = r1 and dst = r1 is invalid)
*/
.macro compute_mpidr_hash dst, rs0, rs1, rs2, mpidr, mask
and \mpidr, \mpidr, \mask @ mask out MPIDR bits
and \dst, \mpidr, #0xff @ mask=aff0
ARM( mov \dst, \dst, lsr \rs0 ) @ dst=aff0>>rs0
THUMB( lsr \dst, \dst, \rs0 )
and \mask, \mpidr, #0xff00 @ mask = aff1
ARM( orr \dst, \dst, \mask, lsr \rs1 ) @ dst|=(aff1>>rs1)
THUMB( lsr \mask, \mask, \rs1 )
THUMB( orr \dst, \dst, \mask )
and \mask, \mpidr, #0xff0000 @ mask = aff2
ARM( orr \dst, \dst, \mask, lsr \rs2 ) @ dst|=(aff2>>rs2)
THUMB( lsr \mask, \mask, \rs2 )
THUMB( orr \dst, \dst, \mask )
.endm
/*
* Save CPU state for a suspend. This saves the CPU general purpose
* registers, and allocates space on the kernel stack to save the CPU
* specific registers and some other data for resume.
* r0 = suspend function arg0
* r1 = suspend function
*/
ENTRY(__cpu_suspend)
stmfd sp!, {r4 - r11, lr}
#ifdef MULTI_CPU
ldr r10, =processor
ldr r4, [r10, #CPU_SLEEP_SIZE] @ size of CPU sleep state
#else
ldr r4, =cpu_suspend_size
#endif
mov r5, sp @ current virtual SP
add r4, r4, #12 @ Space for pgd, virt sp, phys resume fn
sub sp, sp, r4 @ allocate CPU state on stack
stmfd sp!, {r0, r1} @ save suspend func arg and pointer
add r0, sp, #8 @ save pointer to save block
mov r1, r4 @ size of save block
mov r2, r5 @ virtual SP
ldr r3, =sleep_save_sp
ldr r3, [r3, #SLEEP_SAVE_SP_VIRT]
ALT_SMP(mrc p15, 0, r9, c0, c0, 5)
ALT_UP_B(1f)
ldr r8, =mpidr_hash
/*
* This ldmia relies on the memory layout of the mpidr_hash
* struct mpidr_hash.
*/
ldmia r8, {r4-r7} @ r4 = mpidr mask (r5,r6,r7) = l[0,1,2] shifts
compute_mpidr_hash lr, r5, r6, r7, r9, r4
add r3, r3, lr, lsl #2
1:
bl __cpu_suspend_save
adr lr, BSYM(cpu_suspend_abort)
ldmfd sp!, {r0, pc} @ call suspend fn
ENDPROC(__cpu_suspend)
.ltorg
cpu_suspend_abort:
ldmia sp!, {r1 - r3} @ pop phys pgd, virt SP, phys resume fn
teq r0, #0
moveq r0, #1 @ force non-zero value
mov sp, r2
ldmfd sp!, {r4 - r11, pc}
ENDPROC(cpu_suspend_abort)
/*
* r0 = control register value
*/
.align 5
.pushsection .idmap.text,"ax"
ENTRY(cpu_resume_mmu)
ldr r3, =cpu_resume_after_mmu
instr_sync
mcr p15, 0, r0, c1, c0, 0 @ turn on MMU, I-cache, etc
mrc p15, 0, r0, c0, c0, 0 @ read id reg
instr_sync
mov r0, r0
mov r0, r0
mov pc, r3 @ jump to virtual address
ENDPROC(cpu_resume_mmu)
.popsection
cpu_resume_after_mmu:
bl cpu_init @ restore the und/abt/irq banked regs
mov r0, #0 @ return zero on success
ldmfd sp!, {r4 - r11, pc}
ENDPROC(cpu_resume_after_mmu)
/*
* Note: Yes, part of the following code is located into the .data section.
* This is to allow sleep_save_sp to be accessed with a relative load
* while we can't rely on any MMU translation. We could have put
* sleep_save_sp in the .text section as well, but some setups might
* insist on it to be truly read-only.
*/
.data
.align
ENTRY(cpu_resume)
mov r1, #0
ALT_SMP(mrc p15, 0, r0, c0, c0, 5)
ALT_UP_B(1f)
adr r2, mpidr_hash_ptr
ldr r3, [r2]
add r2, r2, r3 @ r2 = struct mpidr_hash phys address
/*
* This ldmia relies on the memory layout of the mpidr_hash
* struct mpidr_hash.
*/
ldmia r2, { r3-r6 } @ r3 = mpidr mask (r4,r5,r6) = l[0,1,2] shifts
compute_mpidr_hash r1, r4, r5, r6, r0, r3
1:
adr r0, _sleep_save_sp
ldr r0, [r0, #SLEEP_SAVE_SP_PHYS]
ldr r0, [r0, r1, lsl #2]
setmode PSR_I_BIT | PSR_F_BIT | SVC_MODE, r1 @ set SVC, irqs off
@ load phys pgd, stack, resume fn
ARM( ldmia r0!, {r1, sp, pc} )
THUMB( ldmia r0!, {r1, r2, r3} )
THUMB( mov sp, r2 )
THUMB( bx r3 )
ENDPROC(cpu_resume)
.align 2
mpidr_hash_ptr:
.long mpidr_hash - . @ mpidr_hash struct offset
.type sleep_save_sp, #object
ENTRY(sleep_save_sp)
_sleep_save_sp:
.space SLEEP_SAVE_SP_SZ @ struct sleep_save_sp
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