ARM: 5580/2: ARM TCM (Tightly-Coupled Memory) support v3

ARM TCM (Tightly-Coupled Memory) handling in Linux

----

Written by Linus Walleij <linus.walleij@stericsson.com>

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.

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.

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.

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.

Code executing inside the ITCM does not "see" any MMU mappings

and e.g. register accesses must be made to physical addresses.

TCM is used for a few things:

- FIQ and other interrupt handlers that need deterministic

  timing and cannot wait for cache misses.

- 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.

- Other operations which implies shutting off or reconfiguring

  the external RAM controller.

There is an interface for using TCM on the ARM architecture

in <asm/tcm.h>. Using this interface it is possible to:

- Define the physical address and size of ITCM and DTCM.

- Tag functions to be compiled into ITCM.

- Tag data and constants to be allocated to DTCM and ITCM.

- 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.

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.

Functions to go into itcm can be tagged like this:

int __tcmfunc foo(int bar);

Variables to go into dtcm can be tagged like this:

int __tcmdata foo;

Constants can be tagged like this:

int __tcmconst foo;

To put assembler into TCM just use

.section ".tcm.text" or .section ".tcm.data"

respectively.

Example code:

#include <asm/tcm.h>

/* Uninitialized data */

static u32 __tcmdata tcmvar;

/* Initialized data */

static u32 __tcmdata tcmassigned = 0x2BADBABEU;

/* Constant */

static const u32 __tcmconst tcmconst = 0xCAFEBABEU;

static void __tcmlocalfunc tcm_to_tcm(void)

{

	int i;

	for (i = 0; i < 100; i++)

		tcmvar ++;

}

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();

}

static void __init test_tcm(void)

{

	u32 *tcmem;

	int i;

	hello_tcm();

	printk("Hello TCM executed from ITCM RAM\n");

	printk("TCM variable from testrun: %u @ %p\n", tcmvar, &tcmvar);

	tcmvar = 0xDEADBEEFU;

	printk("TCM variable: 0x%x @ %p\n", tcmvar, &tcmvar);

	printk("TCM assigned variable: 0x%x @ %p\n", tcmassigned, &tcmassigned);

	printk("TCM constant: 0x%x @ %p\n", tcmconst, &tcmconst);

	/* 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);

	}

}

	depends on GENERIC_CLOCKEVENTS

	default y if SMP && !LOCAL_TIMERS

config HAVE_TCM

	bool

	select GENERIC_ALLOCATOR

config NO_IOPORT

	bool

	bool "ST-Ericsson U300 Series"

	depends on MMU

	select CPU_ARM926T

	select HAVE_TCM

	select ARM_AMBA

	select ARM_VIC

	select GENERIC_TIME

	return read_cpuid(CPUID_CACHETYPE);

}

static inline unsigned int __attribute_const__ read_cpuid_tcmstatus(void)

{

	return read_cpuid(CPUID_TCM);

}

/*

 * Intel's XScale3 core supports some v6 features (supersections, L2)

 * but advertises itself as v5 as it does not support the v6 ISA.  For

/*

 *

 * Copyright (C) 2008-2009 ST-Ericsson AB

 * License terms: GNU General Public License (GPL) version 2

 *

 * Author: Rickard Andersson <rickard.andersson@stericsson.com>

 * Author: Linus Walleij <linus.walleij@stericsson.com>

 *

 */

#ifndef __ASMARM_TCM_H

#define __ASMARM_TCM_H

#ifndef CONFIG_HAVE_TCM

#error "You should not be including tcm.h unless you have a TCM!"

#endif

#include <linux/compiler.h>

/* Tag variables with this */

#define __tcmdata __section(.tcm.data)

/* Tag constants with this */

#define __tcmconst __section(.tcm.rodata)

/* Tag functions inside TCM called from outside TCM with this */

#define __tcmfunc __attribute__((long_call)) __section(.tcm.text) noinline

/* Tag function inside TCM called from inside TCM  with this */

#define __tcmlocalfunc __section(.tcm.text)

void *tcm_alloc(size_t len);

void tcm_free(void *addr, size_t len);

#endif

obj-$(CONFIG_ARM_THUMBEE)	+= thumbee.o

obj-$(CONFIG_KGDB)		+= kgdb.o

obj-$(CONFIG_ARM_UNWIND)	+= unwind.o

obj-$(CONFIG_HAVE_TCM)		+= tcm.o

obj-$(CONFIG_CRUNCH)		+= crunch.o crunch-bits.o

AFLAGS_crunch-bits.o		:= -Wa,-mcpu=ep9312