Re: [RFC PATCH v2 3/5] ARM: kernel: update cpu_suspend code to use cache LoUIS operations
From: Dave Martin <hidden>
Date: 2012-09-19 13:46:58
Also in:
linux-arm-kernel
On Tue, Sep 18, 2012 at 05:35:33PM +0100, Lorenzo Pieralisi wrote:
In processors like A15/A7 L2 cache is unified and integrated within the processor cache hierarchy, so that it is not considered an outer cache anymore. For processors like A15/A7 flush_cache_all() ends up cleaning all cache levels up to Level of Coherency (LoC) that includes the L2 unified cache. When a single CPU is suspended (CPU idle) a complete L2 clean is not required, so generic cpu_suspend code must clean the data cache using the newly introduced cache LoUIS function.
For patches 3-5 in this series, we know that the assumption that flushing LoUIS is sufficient for safely powering the CPU down is not valid in the general case, though we've agreed it's a sensible compromise for the CPU variants we know about today. I think we do need to document this assumption, though. At this point I don't mind whether it appears in code comments or in the commit messages. Cheers ---Dave
quoted hunk ↗ jump to hunk
The context and stack pointer (context pointer) are cleaned to main memory using cache area functions that operate on MVA and guarantee that the data is written back to main memory (perform cache cleaning up to the Point of Coherency - PoC) so that the processor can fetch the context when the MMU is off in the cpu_resume code path. outer_cache management remains unchanged. Reviewed-by: Santosh Shilimkar <redacted> Signed-off-by: Lorenzo Pieralisi <redacted> --- arch/arm/kernel/suspend.c | 17 ++++++++++++++++- 1 file changed, 16 insertions(+), 1 deletion(-)diff --git a/arch/arm/kernel/suspend.c b/arch/arm/kernel/suspend.c index 1794cc3..358bca3 100644 --- a/arch/arm/kernel/suspend.c +++ b/arch/arm/kernel/suspend.c@@ -17,6 +17,8 @@ extern void cpu_resume_mmu(void); */ void __cpu_suspend_save(u32 *ptr, u32 ptrsz, u32 sp, u32 *save_ptr) { + u32 *ctx = ptr; + *save_ptr = virt_to_phys(ptr); /* This must correspond to the LDM in cpu_resume() assembly */@@ -26,7 +28,20 @@ void __cpu_suspend_save(u32 *ptr, u32 ptrsz, u32 sp, u32 *save_ptr) cpu_do_suspend(ptr); - flush_cache_all(); + flush_cache_louis(); + + /* + * flush_cache_louis does not guarantee that + * save_ptr and ptr are cleaned to main memory, + * just up to the Level of Unification Inner Shareable. + * Since the context pointer and context itself + * are to be retrieved with the MMU off that + * data must be cleaned from all cache levels + * to main memory using "area" cache primitives. + */ + __cpuc_flush_dcache_area(ctx, ptrsz); + __cpuc_flush_dcache_area(save_ptr, sizeof(*save_ptr)); + outer_clean_range(*save_ptr, *save_ptr + ptrsz); outer_clean_range(virt_to_phys(save_ptr), virt_to_phys(save_ptr) + sizeof(*save_ptr));-- 1.7.12