From 1c33be57496d927ce05b2513ff0c108f69db4345 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 12 Apr 2012 02:56:10 -0400 Subject: ARM: b.L: core switcher code This is the core code implementing big.LITTLE switcher functionality. Rationale for this code is available here: http://lwn.net/Articles/481055/ The main entry point for a switch request is: void bL_switch_request(unsigned int cpu, unsigned int new_cluster_id) If the calling CPU is not the wanted one, this wrapper takes care of sending the request to the appropriate CPU with schedule_work_on(). At the moment the core switch operation is handled by bL_switch_to() which must be called on the CPU for which a switch is requested. What this code does: * Return early if the current cluster is the wanted one. * Close the gate in the kernel entry vector for both the inbound and outbound CPUs. * Wake up the inbound CPU so it can perform its reset sequence in parallel up to the kernel entry vector gate. * Migrate all interrupts in the GIC targeting the outbound CPU interface to the inbound CPU interface, including SGIs. This is performed by gic_migrate_target() in drivers/irqchip/irq-gic.c. * Call cpu_pm_enter() which takes care of flushing the VFP state to RAM and save the CPU interface config from the GIC to RAM. * Modify the cpu_logical_map to refer to the inbound physical CPU. * Call cpu_suspend() which saves the CPU state (general purpose registers, page table address) onto the stack and store the resulting stack pointer in an array indexed by the updated cpu_logical_map, then call the provided shutdown function. This happens in arch/arm/kernel/sleep.S. At this point, the provided shutdown function executed by the outbound CPU ungates the inbound CPU. Therefore the inbound CPU: * Picks up the saved stack pointer in the array indexed by its MPIDR in arch/arm/kernel/sleep.S. * The MMU and caches are re-enabled using the saved state on the provided stack, just like if this was a resume operation from a suspended state. * Then cpu_suspend() returns, although this is on the inbound CPU rather than the outbound CPU which called it initially. * The function cpu_pm_exit() is called which effect is to restore the CPU interface state in the GIC using the state previously saved by the outbound CPU. * Exit of bL_switch_to() to resume normal kernel execution on the new CPU. However, the outbound CPU is potentially still running in parallel while the inbound CPU is resuming normal kernel execution, hence we need per CPU stack isolation to execute bL_do_switch(). After the outbound CPU has ungated the inbound CPU, it calls mcpm_cpu_power_down() to: * Clean its L1 cache. * If it is the last CPU still alive in its cluster (last man standing), it also cleans its L2 cache and disables cache snooping from the other cluster. * Power down the CPU (or whole cluster). Code called from bL_do_switch() might end up referencing 'current' for some reasons. However, 'current' is derived from the stack pointer. With any arbitrary stack, the returned value for 'current' and any dereferenced values through it are just random garbage which may lead to segmentation faults. The active page table during the execution of bL_do_switch() is also a problem. There is no guarantee that the inbound CPU won't destroy the corresponding task which would free the attached page table while the outbound CPU is still running and relying on it. To solve both issues, we borrow some of the task space belonging to the init/idle task which, by its nature, is lightly used and therefore is unlikely to clash with our usage. The init task is also never going away. Right now the logical CPU number is assumed to be equivalent to the physical CPU number within each cluster. The kernel should also be booted with only one cluster active. These limitations will be lifted eventually. Signed-off-by: Nicolas Pitre --- arch/arm/Kconfig | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 37c0f4e..ade7001 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1538,6 +1538,24 @@ config MCPM for (multi-)cluster based systems, such as big.LITTLE based systems. +config BIG_LITTLE + bool "big.LITTLE support (Experimental)" + depends on CPU_V7 && SMP + select MCPM + help + This option enables support selections for the big.LITTLE + system architecture. + +config BL_SWITCHER + bool "big.LITTLE switcher support" + depends on BIG_LITTLE && MCPM && HOTPLUG_CPU + select CPU_PM + select ARM_CPU_SUSPEND + help + The big.LITTLE "switcher" provides the core functionality to + transparently handle transition between a cluster of A15's + and a cluster of A7's in a big.LITTLE system. + choice prompt "Memory split" default VMSPLIT_3G -- cgit v1.1 From b22537c682671de97c932d5addb6b7d087352aa1 Mon Sep 17 00:00:00 2001 From: Nicolas Pitre Date: Thu, 12 Apr 2012 03:04:28 -0400 Subject: ARM: bL_switcher: add a simple /dev user interface for debugging purposes Only the basic call to aid debugging. *** NOT FOR PRODUCTION *** Usage: echo , > /dev/b.L_switcher where is the logical CPU number, and is 0 for the first cluster and 1 for the second cluster. Signed-off-by: nicolas Pitre --- arch/arm/Kconfig | 8 ++++++++ 1 file changed, 8 insertions(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index ade7001..cfcb0d8 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -1556,6 +1556,14 @@ config BL_SWITCHER transparently handle transition between a cluster of A15's and a cluster of A7's in a big.LITTLE system. +config BL_SWITCHER_DUMMY_IF + tristate "Simple big.LITTLE switcher user interface" + depends on BL_SWITCHER && DEBUG_KERNEL + help + This is a simple and dummy char dev interface to control + the big.LITTLE switcher core code. It is meant for + debugging purposes only. + choice prompt "Memory split" default VMSPLIT_3G -- cgit v1.1 From 49863894db3ed7bd41541b1c17733273966cea71 Mon Sep 17 00:00:00 2001 From: Will Deacon Date: Thu, 26 Sep 2013 12:36:35 +0100 Subject: ARM: perf: add support for perf registers API This patch implements the functions required for the perf registers API, allowing the perf tool to interface kernel register dumps with libunwind in order to provide userspace backtracing. Cc: Jean Pihet Signed-off-by: Will Deacon --- arch/arm/Kconfig | 2 ++ 1 file changed, 2 insertions(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 1ad6fb6..899d0c6 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -51,6 +51,8 @@ config ARM select HAVE_MOD_ARCH_SPECIFIC if ARM_UNWIND select HAVE_OPROFILE if (HAVE_PERF_EVENTS) select HAVE_PERF_EVENTS + select HAVE_PERF_REGS + select HAVE_PERF_USER_STACK_DUMP select HAVE_REGS_AND_STACK_ACCESS_API select HAVE_SYSCALL_TRACEPOINTS select HAVE_UID16 -- cgit v1.1 From d10d2d485497cdc62a7660cd981f8f1ae0dffe7d Mon Sep 17 00:00:00 2001 From: Ben Dooks Date: Fri, 1 Feb 2013 09:41:37 +0000 Subject: ARM: fix ARCH_IXP4xx usage of ARCH_SUPPORTS_BIG_ENDIAN The Kconfig for arch/arm/mach-ixp4xx has a local definition of ARCH_SUPPORTS_BIG_ENDIAN which could be used elsewhere. This means that if IXP4xx is selected and this symbol is selected eleswhere then an warning is produced. Clean the following error up by making the symbol be selected by the main ARCH_IXP4XX definition and have a common definition in arch/arm/mm/Kconfig warning: (ARCH_xxx) selects ARCH_SUPPORTS_BIG_ENDIAN which has unmet direct dependencies (ARCH_IXP4XX) warning: (ARCH_xxx) selects ARCH_SUPPORTS_BIG_ENDIAN which has unmet direct dependencies (ARCH_IXP4XX) Signed-off-by: Ben Dooks --- arch/arm/Kconfig | 1 + 1 file changed, 1 insertion(+) (limited to 'arch/arm/Kconfig') diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig index 1ad6fb6..f048e14 100644 --- a/arch/arm/Kconfig +++ b/arch/arm/Kconfig @@ -481,6 +481,7 @@ config ARCH_IXP4XX bool "IXP4xx-based" depends on MMU select ARCH_HAS_DMA_SET_COHERENT_MASK + select ARCH_SUPPORTS_BIG_ENDIAN select ARCH_REQUIRE_GPIOLIB select CLKSRC_MMIO select CPU_XSCALE -- cgit v1.1