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Merge branch 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm
* 'for-linus' of master.kernel.org:/home/rmk/linux-2.6-arm: (103 commits) ARM: 5719/1: [AT91] Fix AC97 breakage ARM: 5721/1: MMCI enable the use of a regulator ARM: 5720/1: Move MMCI header to amba include dir ARM: 5718/1: Sane busids for RealView board components ARM: 5715/1: Make kprobes unregistration SMP safe ARM: 5711/1: locomo.c: CodingStyle cleanups ARM: 5710/1: at91: add AC97 support to at91sam9rl and at91sam9rlek board ARM: 5709/1: at91: add AC97 support to at91sam9g45 series and at91sam9m10g45ek board ARM: 5621/1: at91/dmaengine: integration of at_hdmac driver in at91sam9g45 series ARM: 5620/1: at91/dmaengine: integration of at_hdmac driver in at91sam9rl ARM: Add support for checking access permissions on prefetch aborts ARM: Separate out access error checking ARM: Ensure correct might_sleep() check in pagefault path ARM: Update page fault handling for new OOM techniques ARM: Provide definitions and helpers for decoding the FSR register ARM: 5712/1: SA1100: initialise spinlock in DMA code ARM: s3c: fix check of index into s3c_gpios[] ARM: spitz: fix touchscreen max presure ARM: STMP3xxx: deallocation with negative index of descriptors[] Thumb-2: Correctly handle undefined instructions in the kernel ...
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| ARM TCM (Tightly-Coupled Memory) handling in Linux | ||
| ---- | ||
| Written by Linus Walleij <linus.walleij@stericsson.com> | ||
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| Some ARM SoC:s have a so-called TCM (Tightly-Coupled Memory). | ||
| This is usually just a few (4-64) KiB of RAM inside the ARM | ||
| processor. | ||
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| Due to being embedded inside the CPU The TCM has a | ||
| Harvard-architecture, so there is an ITCM (instruction TCM) | ||
| and a DTCM (data TCM). The DTCM can not contain any | ||
| instructions, but the ITCM can actually contain data. | ||
| The size of DTCM or ITCM is minimum 4KiB so the typical | ||
| minimum configuration is 4KiB ITCM and 4KiB DTCM. | ||
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| ARM CPU:s have special registers to read out status, physical | ||
| location and size of TCM memories. arch/arm/include/asm/cputype.h | ||
| defines a CPUID_TCM register that you can read out from the | ||
| system control coprocessor. Documentation from ARM can be found | ||
| at http://infocenter.arm.com, search for "TCM Status Register" | ||
| to see documents for all CPUs. Reading this register you can | ||
| determine if ITCM (bit 0) and/or DTCM (bit 16) is present in the | ||
| machine. | ||
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| There is further a TCM region register (search for "TCM Region | ||
| Registers" at the ARM site) that can report and modify the location | ||
| size of TCM memories at runtime. This is used to read out and modify | ||
| TCM location and size. Notice that this is not a MMU table: you | ||
| actually move the physical location of the TCM around. At the | ||
| place you put it, it will mask any underlying RAM from the | ||
| CPU so it is usually wise not to overlap any physical RAM with | ||
| the TCM. The TCM memory exists totally outside the MMU and will | ||
| override any MMU mappings. | ||
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| Code executing inside the ITCM does not "see" any MMU mappings | ||
| and e.g. register accesses must be made to physical addresses. | ||
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| TCM is used for a few things: | ||
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| - FIQ and other interrupt handlers that need deterministic | ||
| timing and cannot wait for cache misses. | ||
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| - Idle loops where all external RAM is set to self-refresh | ||
| retention mode, so only on-chip RAM is accessible by | ||
| the CPU and then we hang inside ITCM waiting for an | ||
| interrupt. | ||
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| - Other operations which implies shutting off or reconfiguring | ||
| the external RAM controller. | ||
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| There is an interface for using TCM on the ARM architecture | ||
| in <asm/tcm.h>. Using this interface it is possible to: | ||
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| - Define the physical address and size of ITCM and DTCM. | ||
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| - Tag functions to be compiled into ITCM. | ||
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| - Tag data and constants to be allocated to DTCM and ITCM. | ||
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| - Have the remaining TCM RAM added to a special | ||
| allocation pool with gen_pool_create() and gen_pool_add() | ||
| and provice tcm_alloc() and tcm_free() for this | ||
| memory. Such a heap is great for things like saving | ||
| device state when shutting off device power domains. | ||
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| A machine that has TCM memory shall select HAVE_TCM in | ||
| arch/arm/Kconfig for itself, and then the | ||
| rest of the functionality will depend on the physical | ||
| location and size of ITCM and DTCM to be defined in | ||
| mach/memory.h for the machine. Code that needs to use | ||
| TCM shall #include <asm/tcm.h> If the TCM is not located | ||
| at the place given in memory.h it will be moved using | ||
| the TCM Region registers. | ||
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| Functions to go into itcm can be tagged like this: | ||
| int __tcmfunc foo(int bar); | ||
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| Variables to go into dtcm can be tagged like this: | ||
| int __tcmdata foo; | ||
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| Constants can be tagged like this: | ||
| int __tcmconst foo; | ||
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| To put assembler into TCM just use | ||
| .section ".tcm.text" or .section ".tcm.data" | ||
| respectively. | ||
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| Example code: | ||
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| #include <asm/tcm.h> | ||
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| /* Uninitialized data */ | ||
| static u32 __tcmdata tcmvar; | ||
| /* Initialized data */ | ||
| static u32 __tcmdata tcmassigned = 0x2BADBABEU; | ||
| /* Constant */ | ||
| static const u32 __tcmconst tcmconst = 0xCAFEBABEU; | ||
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| static void __tcmlocalfunc tcm_to_tcm(void) | ||
| { | ||
| int i; | ||
| for (i = 0; i < 100; i++) | ||
| tcmvar ++; | ||
| } | ||
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| static void __tcmfunc hello_tcm(void) | ||
| { | ||
| /* Some abstract code that runs in ITCM */ | ||
| int i; | ||
| for (i = 0; i < 100; i++) { | ||
| tcmvar ++; | ||
| } | ||
| tcm_to_tcm(); | ||
| } | ||
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| static void __init test_tcm(void) | ||
| { | ||
| u32 *tcmem; | ||
| int i; | ||
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| hello_tcm(); | ||
| printk("Hello TCM executed from ITCM RAM\n"); | ||
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| printk("TCM variable from testrun: %u @ %p\n", tcmvar, &tcmvar); | ||
| tcmvar = 0xDEADBEEFU; | ||
| printk("TCM variable: 0x%x @ %p\n", tcmvar, &tcmvar); | ||
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| printk("TCM assigned variable: 0x%x @ %p\n", tcmassigned, &tcmassigned); | ||
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| printk("TCM constant: 0x%x @ %p\n", tcmconst, &tcmconst); | ||
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| /* Allocate some TCM memory from the pool */ | ||
| tcmem = tcm_alloc(20); | ||
| if (tcmem) { | ||
| printk("TCM Allocated 20 bytes of TCM @ %p\n", tcmem); | ||
| tcmem[0] = 0xDEADBEEFU; | ||
| tcmem[1] = 0x2BADBABEU; | ||
| tcmem[2] = 0xCAFEBABEU; | ||
| tcmem[3] = 0xDEADBEEFU; | ||
| tcmem[4] = 0x2BADBABEU; | ||
| for (i = 0; i < 5; i++) | ||
| printk("TCM tcmem[%d] = %08x\n", i, tcmem[i]); | ||
| tcm_free(tcmem, 20); | ||
| } | ||
| } |
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