From 7604537bbb5720376e8c9e6bc74a8e6305e3094d Mon Sep 17 00:00:00 2001 From: Lorenzo Pieralisi Date: Thu, 16 May 2013 10:34:30 +0100 Subject: 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 Cc: Catalin Marinas Cc: Russell King Cc: Colin Cross Cc: Santosh Shilimkar Cc: Daniel Lezcano Cc: Amit Kucheria Signed-off-by: Lorenzo Pieralisi Reviewed-by: Dave Martin Reviewed-by: Nicolas Pitre Tested-by: Shawn Guo Tested-by: Kevin Hilman Tested-by: Stephen Warren --- arch/arm/kernel/asm-offsets.c | 6 ++++++ 1 file changed, 6 insertions(+) (limited to 'arch/arm/kernel/asm-offsets.c') diff --git a/arch/arm/kernel/asm-offsets.c b/arch/arm/kernel/asm-offsets.c index ee68cce6b48e..ded041711beb 100644 --- a/arch/arm/kernel/asm-offsets.c +++ b/arch/arm/kernel/asm-offsets.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include @@ -144,6 +145,11 @@ int main(void) #endif #ifdef MULTI_CACHE DEFINE(CACHE_FLUSH_KERN_ALL, offsetof(struct cpu_cache_fns, flush_kern_all)); +#endif +#ifdef CONFIG_ARM_CPU_SUSPEND + DEFINE(SLEEP_SAVE_SP_SZ, sizeof(struct sleep_save_sp)); + DEFINE(SLEEP_SAVE_SP_PHYS, offsetof(struct sleep_save_sp, save_ptr_stash_phys)); + DEFINE(SLEEP_SAVE_SP_VIRT, offsetof(struct sleep_save_sp, save_ptr_stash)); #endif BLANK(); DEFINE(DMA_BIDIRECTIONAL, DMA_BIDIRECTIONAL); -- cgit