Subject: [PATCH v9 1/3] ARM: Add base support for ARMv7-M

From: [email-masked] (Jonathan Austin)
Date: Fri, 22 Mar 2013 18:42:53 +0000

Hi Uwe,

This looks like a good set of changes! Things are much cleaner now - 
just a question about the nop cache functions and a few other things 
below - some of them are just tiny little things...

On 21/03/13 21:28, Uwe Kleine-K?nig wrote:
> From: Catalin Marinas <[email-masked]>
>
> This patch adds the base support for the ARMv7-M
> architecture. It consists of the corresponding arch/arm/mm/ files and
> various #ifdef's around the kernel. Exception handling is implemented by
> a subsequent patch.
>
> [ukleinek: squash in some changes originating from commit
>
> b5717ba (Cortex-M3: Add support for the Microcontroller Prototyping System)
>
> from the v2.6.33-arm1 patch stack, port to post 3.6, drop zImage
> support, drop reorganisation of pt_regs, assert CONFIG_V7M doesn't leak
> into installed headers and a few cosmetic changes]
>
> Signed-off-by: Catalin Marinas <[email-masked]>
> Signed-off-by: Uwe Kleine-K?nig <[email-masked]>
> ---
> Changes since v8,
> id:1358413196-5609-3-git-send-email-u.kleine-koenig at pengutronix.de:
>
>   - rebase
>   - use more named constants
>   - add comment about setmode being empty
>   - add more (yet unused) v7m register defines
>   - enable UsageFault, BusFault and MemManage fault at boot time
>   - make nop multi-cache-able
> ---
>   arch/arm/include/asm/assembler.h   |  17 +++-
>   arch/arm/include/asm/cputype.h     |  12 ++-
>   arch/arm/include/asm/glue-cache.h  |  27 ++++++
>   arch/arm/include/asm/glue-df.h     |   8 ++
>   arch/arm/include/asm/glue-proc.h   |   9 ++
>   arch/arm/include/asm/irqflags.h    |  22 +++--
>   arch/arm/include/asm/ptrace.h      |   4 +
>   arch/arm/include/asm/system_info.h |   1 +
>   arch/arm/include/asm/v7m.h         |  47 +++++++++++
>   arch/arm/include/uapi/asm/ptrace.h |  35 ++++++--
>   arch/arm/kernel/head-nommu.S       |  10 ++-
>   arch/arm/kernel/setup.c            |  17 +++-
>   arch/arm/kernel/traps.c            |   2 +
>   arch/arm/mm/cache-nop.S            |  53 ++++++++++++
>   arch/arm/mm/nommu.c                |   2 +
>   arch/arm/mm/proc-v7m.S             | 167 +++++++++++++++++++++++++++++++++++++
>   16 files changed, 412 insertions(+), 21 deletions(-)
>   create mode 100644 arch/arm/include/asm/v7m.h
>   create mode 100644 arch/arm/mm/cache-nop.S
>   create mode 100644 arch/arm/mm/proc-v7m.S
>
> diff --git a/arch/arm/include/asm/assembler.h b/arch/arm/include/asm/assembler.h
> index 05ee9ee..a5fef71 100644
> --- a/arch/arm/include/asm/assembler.h
> +++ b/arch/arm/include/asm/assembler.h
> @@ -136,7 +136,11 @@
>    * assumes FIQs are enabled, and that the processor is in SVC mode.
>    */
>          .macro  save_and_disable_irqs, oldcpsr
> +#ifdef CONFIG_CPU_V7M
> +       mrs     \oldcpsr, primask
> +#else
>          mrs     \oldcpsr, cpsr
> +#endif
>          disable_irq
>          .endm
>
> @@ -150,7 +154,11 @@
>    * guarantee that this will preserve the flags.
>    */
>          .macro  restore_irqs_notrace, oldcpsr
> +#ifdef CONFIG_CPU_V7M
> +       msr     primask, \oldcpsr
> +#else
>          msr     cpsr_c, \oldcpsr
> +#endif
>          .endm
>
>          .macro restore_irqs, oldcpsr
> @@ -229,7 +237,14 @@
>   #endif
>          .endm
>
> -#ifdef CONFIG_THUMB2_KERNEL
> +#if defined(CONFIG_CPU_V7M)
> +       /*
> +        * setmode is used to assert to be in svc mode during boot. For v7-M
> +        * this is done in __v7m_setup, so setmode can be empty here.
> +        */
> +       .macro  setmode, mode, reg
> +       .endm
> +#elif defined(CONFIG_THUMB2_KERNEL)
>          .macro  setmode, mode, reg
>          mov     \reg, #\mode
>          msr     cpsr_c, \reg
> diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
> index 7652712..d7eb0fb 100644
> --- a/arch/arm/include/asm/cputype.h
> +++ b/arch/arm/include/asm/cputype.h
> @@ -106,7 +106,17 @@ static inline unsigned int __attribute_const__ read_cpuid_id(void)
>          return read_cpuid(CPUID_ID);
>   }
>
> -#else /* ifdef CONFIG_CPU_CP15 */
> +#elif defined(CONFIG_CPU_V7M)
> +
> +#include <asm/io.h>
> +#include <asm/v7m.h>
> +
> +static inline unsigned int __attribute_const__ read_cpuid_id(void)
> +{
> +       return readl(V7M_SCS_CPUID);
> +}
> +
> +#else /* ifdef CONFIG_CPU_CP15 / elif defined(CONFIG_CPU_V7M) */
>
>   static inline unsigned int __attribute_const__ read_cpuid_id(void)
>   {
> diff --git a/arch/arm/include/asm/glue-cache.h b/arch/arm/include/asm/glue-cache.h
> index cca9f15..65c9faf 100644
> --- a/arch/arm/include/asm/glue-cache.h
> +++ b/arch/arm/include/asm/glue-cache.h
> @@ -125,10 +125,37 @@
>   # endif
>   #endif
>
> +#if defined(CONFIG_CPU_V7M)
> +# ifdef _CACHE
> +#  define MULTI_CACHE 1
> +# else
> +#  define _CACHE nop
> +# endif
> +#endif
> +
>   #if !defined(_CACHE) && !defined(MULTI_CACHE)
>   #error Unknown cache maintenance model
>   #endif
>
> +#ifndef __ASSEMBLER__
> +extern inline void nop_flush_icache_all(void) { }
> +extern inline void nop_flush_kern_cache_all(void) { }
> +extern inline void nop_flush_kern_cache_louis(void) { }
> +extern inline void nop_flush_user_cache_all(void) { }
> +extern inline void nop_flush_user_cache_range(unsigned long a,
> +               unsigned long b, unsigned int c) { }
> +
> +extern inline void nop_coherent_kern_range(unsigned long a, unsigned long b) { }
> +extern inline int nop_coherent_user_range(unsigned long a,
> +               unsigned long b) { return 0; }
> +extern inline void nop_flush_kern_dcache_area(void *a, size_t s) { }
> +
> +extern inline void nop_dma_flush_range(const void *a, const void *b) { }
> +
> +extern inline void nop_dma_map_area(const void *s, size_t l, int f) { }
> +extern inline void nop_dma_unmap_area(const void *s, size_t l, int f) { }
> +#endif
> +

Now that you've added the arch/arm/mm/cache-nop.S do we really need 
these defines? I just tried removing them and it still builds - is there 
a use-case for these I missed?

>   #ifndef MULTI_CACHE
>   #define __cpuc_flush_icache_all                __glue(_CACHE,_flush_icache_all)
>   #define __cpuc_flush_kern_all          __glue(_CACHE,_flush_kern_cache_all)
> diff --git a/arch/arm/include/asm/glue-df.h b/arch/arm/include/asm/glue-df.h
> index b6e9f2c..6b70f1b 100644
> --- a/arch/arm/include/asm/glue-df.h
> +++ b/arch/arm/include/asm/glue-df.h
> @@ -95,6 +95,14 @@
>   # endif
>   #endif
>
> +#ifdef CONFIG_CPU_ABRT_NOMMU
> +# ifdef CPU_DABORT_HANDLER
> +#  define MULTI_DABORT 1
> +# else
> +#  define CPU_DABORT_HANDLER nommu_early_abort
> +# endif
> +#endif
> +
>   #ifndef CPU_DABORT_HANDLER
>   #error Unknown data abort handler type
>   #endif
> diff --git a/arch/arm/include/asm/glue-proc.h b/arch/arm/include/asm/glue-proc.h
> index ac1dd54..f2f39bc 100644
> --- a/arch/arm/include/asm/glue-proc.h
> +++ b/arch/arm/include/asm/glue-proc.h
> @@ -230,6 +230,15 @@
>   # endif
>   #endif
>
> +#ifdef CONFIG_CPU_V7M
> +# ifdef CPU_NAME
> +#  undef  MULTI_CPU
> +#  define MULTI_CPU
> +# else
> +#  define CPU_NAME cpu_v7m
> +# endif
> +#endif
> +
>   #ifndef MULTI_CPU
>   #define cpu_proc_init                  __glue(CPU_NAME,_proc_init)
>   #define cpu_proc_fin                   __glue(CPU_NAME,_proc_fin)
> diff --git a/arch/arm/include/asm/irqflags.h b/arch/arm/include/asm/irqflags.h
> index 1e6cca5..3b763d6 100644
> --- a/arch/arm/include/asm/irqflags.h
> +++ b/arch/arm/include/asm/irqflags.h
> @@ -8,6 +8,16 @@
>   /*
>    * CPU interrupt mask handling.
>    */
> +#ifdef CONFIG_CPU_V7M
> +#define IRQMASK_REG_NAME_R "primask"
> +#define IRQMASK_REG_NAME_W "primask"
> +#define IRQMASK_I_BIT  1
> +#else
> +#define IRQMASK_REG_NAME_R "cpsr"
> +#define IRQMASK_REG_NAME_W "cpsr_c"
> +#define IRQMASK_I_BIT  PSR_I_BIT
> +#endif
> +
>   #if __LINUX_ARM_ARCH__ >= 6
>
>   static inline unsigned long arch_local_irq_save(void)
> @@ -15,7 +25,7 @@ static inline unsigned long arch_local_irq_save(void)
>          unsigned long flags;
>
>          asm volatile(
> -               "       mrs     %0, cpsr        @ arch_local_irq_save\n"
> +               "       mrs     %0, " IRQMASK_REG_NAME_R "      @ arch_local_irq_save\n"
>                  "       cpsid   i"
>                  : "=r" (flags) : : "memory", "cc");
>          return flags;
> @@ -129,7 +139,7 @@ static inline unsigned long arch_local_save_flags(void)
>   {
>          unsigned long flags;
>          asm volatile(
> -               "       mrs     %0, cpsr        @ local_save_flags"
> +               "       mrs     %0, " IRQMASK_REG_NAME_R "      @ local_save_flags"
>                  : "=r" (flags) : : "memory", "cc");
>          return flags;
>   }
> @@ -140,7 +150,7 @@ static inline unsigned long arch_local_save_flags(void)
>   static inline void arch_local_irq_restore(unsigned long flags)
>   {
>          asm volatile(
> -               "       msr     cpsr_c, %0      @ local_irq_restore"
> +               "       msr     " IRQMASK_REG_NAME_W ", %0      @ local_irq_restore"
>                  :
>                  : "r" (flags)
>                  : "memory", "cc");
> @@ -148,8 +158,8 @@ static inline void arch_local_irq_restore(unsigned long flags)
>
>   static inline int arch_irqs_disabled_flags(unsigned long flags)
>   {
> -       return flags & PSR_I_BIT;
> +       return flags & IRQMASK_I_BIT;
>   }
>
> -#endif
> -#endif
> +#endif /* ifdef __KERNEL__ */
> +#endif /* ifndef __ASM_ARM_IRQFLAGS_H */
> diff --git a/arch/arm/include/asm/ptrace.h b/arch/arm/include/asm/ptrace.h
> index 3d52ee1..04c99f3 100644
> --- a/arch/arm/include/asm/ptrace.h
> +++ b/arch/arm/include/asm/ptrace.h
> @@ -45,6 +45,7 @@ struct pt_regs {
>    */
>   static inline int valid_user_regs(struct pt_regs *regs)
>   {
> +#ifndef CONFIG_CPU_V7M
>          unsigned long mode = regs->ARM_cpsr & MODE_MASK;
>
>          /*
> @@ -67,6 +68,9 @@ static inline int valid_user_regs(struct pt_regs *regs)
>                  regs->ARM_cpsr |= USR_MODE;
>
>          return 0;
> +#else /* ifndef CONFIG_CPU_V7M */
> +       return 1;
> +#endif
>   }
>
>   static inline long regs_return_value(struct pt_regs *regs)
> diff --git a/arch/arm/include/asm/system_info.h b/arch/arm/include/asm/system_info.h
> index dfd386d..720ea03 100644
> --- a/arch/arm/include/asm/system_info.h
> +++ b/arch/arm/include/asm/system_info.h
> @@ -11,6 +11,7 @@
>   #define CPU_ARCH_ARMv5TEJ      7
>   #define CPU_ARCH_ARMv6         8
>   #define CPU_ARCH_ARMv7         9
> +#define CPU_ARCH_ARMv7M                10
>
>   #ifndef __ASSEMBLY__
>
> diff --git a/arch/arm/include/asm/v7m.h b/arch/arm/include/asm/v7m.h
> new file mode 100644
> index 0000000..e12b887
> --- /dev/null
> +++ b/arch/arm/include/asm/v7m.h
> @@ -0,0 +1,47 @@
> +/*
> + * Common defines for v7m cpus
> + */
> +#define V7M_SCS_ICTR   IOMEM(0xe000e004)
> +#define V7M_SCS_ICTR_INTLINESNUM_MASK          0x0000000f
> +
> +#define V7M_SCS_CPUID  IOMEM(0xe000ed00)
> +

This is really the CPUID_BASE register, not the 'CPUID' register.

> +#define V7M_SCS_ICSR   IOMEM(0xe000ed04)
> +#define V7M_SCS_ICSR_PENDSVSET                 (1 << 28)
> +#define V7M_SCS_ICSR_PENDSVCLR                 (1 << 27)
> +#define V7M_SCS_ICSR_RETTOBASE                 (1 << 11)
> +
> +#define V7M_SCS_VTOR   IOMEM(0xe000ed08)
> +
> +#define V7M_SCS_SCR    IOMEM(0xe000ed10)
> +#define V7M_SCS_SCR_SLEEPDEEP                  (1 << 2)
> +
> +#define V7M_SCS_CCR    IOMEM(0xe000ed14)
> +#define V7M_SCS_CCR_STKALIGN                   (1 << 9)
> +
> +#define V7M_SCS_SHPR2  IOMEM(0xe000ed1c)
> +#define V7M_SCS_SHPR3  IOMEM(0xe000ed20)

This is just a minor nit, but when reading these it is confusing not to 
have the IOMEM(...) lines aligned with the bitfields...

Did you have some reasons for doing it this way?

If not, I'd like to see them all lined up (and you can remove one 
tabstop too ;-)

> +
> +#define V7M_SCS_SHCSR  IOMEM(0xe000ed24)
> +#define V7M_SCS_SHCSR_USGFAULTENA              (1 << 18)
> +#define V7M_SCS_SHCSR_BUSFAULTENA              (1 << 17)
> +#define V7M_SCS_SHCSR_MEMFAULTENA              (1 << 16)
> +
> +#define V7M_xPSR_FPALIGN                       0x00000200
> +
> +#define EXC_RET_SBOP                           0xffffffe1
> +#define EXC_RET_FRAMETYPE_MASK                 0x00000010
> +#define EXC_RET_FRAMETYPE__BASIC               0x00000010
> +#define EXC_RET_MODE_MASK                      0x00000008
> +#define EXC_RET_MODE__HANDLER                  0x00000000
> +#define EXC_RET_MODE__THREAD                   0x00000008
> +#define EXC_RET_STACK_MASK                     0x00000004
> +#define EXC_RET_STACK__MAIN                    0x00000000
> +#define EXC_RET_STACK__PROCESS                 0x00000004

I grep'd around the source tree looking for a precedent for this double 
underscore behaviour and couldn't find anything.

I presume that you're trying to denote that these are values 'served by' 
the mask above?

I think the double underscore looks weird - made me think it was a 
typo... I think you could safely stick with just one, or if you're 
really concerned about the extra distinction, use EXC_RET_STACK_VAL_MAIN 
etc.

> +
> +#define EXC_RET_HANDLERMODE_MAINSTACK  \
> +       (EXC_RET_SBOP | EXC_RET_FRAMETYPE__BASIC | EXC_RET_MODE__HANDLER | EXC_RET_STACK__MAIN)
> +#define EXC_RET_THREADMODE_MAINSTACK   \
> +       (EXC_RET_SBOP | EXC_RET_FRAMETYPE__BASIC | EXC_RET_MODE__THREAD | EXC_RET_STACK__MAIN)

Do we ever use these two? I can't find any places where we do in 
uwe/efm32. If not, I think perhaps this is a bit over-engineered... If 
you plan to extend the kernel port in the future to use the extra modes, 
by all means keep them in, but couldn't we just define 
EXC_RET_THREADMODE_PROCESSSTACK? (or even call it EXC_RET_THREAD_PROCESS?)

> +#define EXC_RET_THREADMODE_PROCESSSTACK        \
> +       (EXC_RET_SBOP | EXC_RET_FRAMETYPE__BASIC | EXC_RET_MODE__THREAD | EXC_RET_STACK__PROCESS)
> diff --git a/arch/arm/include/uapi/asm/ptrace.h b/arch/arm/include/uapi/asm/ptrace.h
> index 96ee092..5af0ed1 100644
> --- a/arch/arm/include/uapi/asm/ptrace.h
> +++ b/arch/arm/include/uapi/asm/ptrace.h
> @@ -34,28 +34,47 @@
>
>   /*
>    * PSR bits
> + * Note on V7M there is no mode contained in the PSR
>    */
>   #define USR26_MODE     0x00000000
>   #define FIQ26_MODE     0x00000001
>   #define IRQ26_MODE     0x00000002
>   #define SVC26_MODE     0x00000003
> +#if defined(__KERNEL__) && defined(CONFIG_CPU_V7M)
> +/*
> + * Use 0 here to get code right that creates a userspace
> + * or kernel space thread.
> + */
> +#define USR_MODE       0x00000000
> +#define SVC_MODE       0x00000000
> +#else
>   #define USR_MODE       0x00000010
> +#define SVC_MODE       0x00000013
> +#endif
>   #define FIQ_MODE       0x00000011
>   #define IRQ_MODE       0x00000012
> -#define SVC_MODE       0x00000013
>   #define ABT_MODE       0x00000017
>   #define HYP_MODE       0x0000001a
>   #define UND_MODE       0x0000001b
>   #define SYSTEM_MODE    0x0000001f
>   #define MODE32_BIT     0x00000010
>   #define MODE_MASK      0x0000001f
> -#define PSR_T_BIT      0x00000020
> -#define PSR_F_BIT      0x00000040
> -#define PSR_I_BIT      0x00000080
> -#define PSR_A_BIT      0x00000100
> -#define PSR_E_BIT      0x00000200
> -#define PSR_J_BIT      0x01000000
> -#define PSR_Q_BIT      0x08000000
> +
> +#define V4_PSR_T_BIT   0x00000020      /* >= V4T, but not V7M */
> +#define V7M_PSR_T_BIT  0x01000000
> +#if defined(__KERNEL__) && defined(CONFIG_CPU_V7M)
> +#define PSR_T_BIT      V7M_PSR_T_BIT
> +#else
> +/* for compatibility */
> +#define PSR_T_BIT      V4_PSR_T_BIT
> +#endif
> +
> +#define PSR_F_BIT      0x00000040      /* >= V4, but not V7M */
> +#define PSR_I_BIT      0x00000080      /* >= V4, but not V7M */
> +#define PSR_A_BIT      0x00000100      /* >= V6, but not V7M */
> +#define PSR_E_BIT      0x00000200      /* >= V6, but not V7M */
> +#define PSR_J_BIT      0x01000000      /* >= V5J, but not V7M */
> +#define PSR_Q_BIT      0x08000000      /* >= V5E, including V7M */
>   #define PSR_V_BIT      0x10000000
>   #define PSR_C_BIT      0x20000000
>   #define PSR_Z_BIT      0x40000000
> diff --git a/arch/arm/kernel/head-nommu.S b/arch/arm/kernel/head-nommu.S
> index 6a2e09c..e2988bb 100644
> --- a/arch/arm/kernel/head-nommu.S
> +++ b/arch/arm/kernel/head-nommu.S
> @@ -19,6 +19,7 @@
>   #include <asm/asm-offsets.h>
>   #include <asm/cp15.h>
>   #include <asm/thread_info.h>
> +#include <asm/v7m.h>
>
>   /*
>    * Kernel startup entry point.
> @@ -50,10 +51,13 @@ ENTRY(stext)
>
>          setmode PSR_F_BIT | PSR_I_BIT | SVC_MODE, r9 @ ensure svc mode
>                                                  @ and irqs disabled
> -#ifndef CONFIG_CPU_CP15
> -       ldr     r9, =CONFIG_PROCESSOR_ID
> -#else
> +#if defined(CONFIG_CPU_CP15)
>          mrc     p15, 0, r9, c0, c0              @ get processor id
> +#elif defined(CONFIG_CPU_V7M)
> +       ldr     r9, =V7M_SCS_CPUID

If you do choose to rename to CPUID_BASE then fix this up too :)

> +       ldr     r9, [r9]
> +#else
> +       ldr     r9, =CONFIG_PROCESSOR_ID
>   #endif
>          bl      __lookup_processor_type         @ r5=procinfo r9=cpuid
>          movs    r10, r5                         @ invalid processor (r5=0)?
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 1cc9e17..8291245 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -128,7 +128,9 @@ struct stack {
>          u32 und[3];
>   } ____cacheline_aligned;
>
> +#ifndef CONFIG_CPU_V7M
>   static struct stack stacks[NR_CPUS];
> +#endif
>
>   char elf_platform[ELF_PLATFORM_SIZE];
>   EXPORT_SYMBOL(elf_platform);
> @@ -207,7 +209,7 @@ static const char *proc_arch[] = {
>          "5TEJ",
>          "6TEJ",
>          "7",
> -       "?(11)",
> +       "7M",
>          "?(12)",
>          "?(13)",
>          "?(14)",
> @@ -216,6 +218,12 @@ static const char *proc_arch[] = {
>          "?(17)",
>   };
>
> +#ifdef CONFIG_CPU_V7M
> +static int __get_cpu_architecture(void)
> +{
> +       return CPU_ARCH_ARMv7M;
> +}
> +#else
>   static int __get_cpu_architecture(void)
>   {
>          int cpu_arch;
> @@ -248,6 +256,7 @@ static int __get_cpu_architecture(void)
>
>          return cpu_arch;
>   }
> +#endif
>
>   int __pure cpu_architecture(void)
>   {
> @@ -293,7 +302,9 @@ static void __init cacheid_init(void)
>   {
>          unsigned int arch = cpu_architecture();
>
> -       if (arch >= CPU_ARCH_ARMv6) {
> +       if (arch == CPU_ARCH_ARMv7M) {
> +               cacheid = 0;
> +       } else if (arch >= CPU_ARCH_ARMv6) {
>                  unsigned int cachetype = read_cpuid_cachetype();
>                  if ((cachetype & (7 << 29)) == 4 << 29) {
>                          /* ARMv7 register format */
> @@ -375,6 +386,7 @@ static void __init feat_v6_fixup(void)
>    */
>   void cpu_init(void)
>   {
> +#ifndef CONFIG_CPU_V7M
>          unsigned int cpu = smp_processor_id();
>          struct stack *stk = &stacks[cpu];
>
> @@ -425,6 +437,7 @@ void cpu_init(void)
>                "I" (offsetof(struct stack, und[0])),
>                PLC (PSR_F_BIT | PSR_I_BIT | SVC_MODE)
>              : "r14");
> +#endif
>   }
>
>   int __cpu_logical_map[NR_CPUS];
> diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
> index 1c08911..3990eaa 100644
> --- a/arch/arm/kernel/traps.c
> +++ b/arch/arm/kernel/traps.c
> @@ -819,6 +819,7 @@ static void __init kuser_get_tls_init(unsigned long vectors)
>
>   void __init early_trap_init(void *vectors_base)
>   {
> +#ifndef CONFIG_CPU_V7M

I think a comment would be nice, just so as not to scare people who 
expect us to need to copy the vector table somewhere.

/* V7M allows us to use the vector_table in the kernel image */

Or similar.
>          unsigned long vectors = (unsigned long)vectors_base;
>          extern char __stubs_start[], __stubs_end[];
>          extern char __vectors_start[], __vectors_end[];
> @@ -850,4 +851,5 @@ void __init early_trap_init(void *vectors_base)
>
>          flush_icache_range(vectors, vectors + PAGE_SIZE);
>          modify_domain(DOMAIN_USER, DOMAIN_CLIENT);
> +#endif
>   }
> diff --git a/arch/arm/mm/cache-nop.S b/arch/arm/mm/cache-nop.S
> new file mode 100644
> index 0000000..543b930
> --- /dev/null
> +++ b/arch/arm/mm/cache-nop.S
> @@ -0,0 +1,53 @@
> +/*
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + */
> +#include <linux/linkage.h>
> +#include <linux/init.h>
> +#include <asm/assembler.h>
> +#include <asm/errno.h>
> +#include <asm/unwind.h>
> +
> +#include "proc-macros.S"
> +
> +ENTRY(nop_flush_icache_all)
> +       mov     pc, lr
> +ENDPROC(nop_flush_icache_all)
> +
> +       .globl nop_flush_kern_cache_all
> +       .equ nop_flush_kern_cache_all, nop_flush_icache_all
> +
> +       .globl nop_flush_kern_cache_louis
> +       .equ nop_flush_kern_cache_louis, nop_flush_icache_all
> +
> +       .globl nop_flush_user_cache_all
> +       .equ nop_flush_user_cache_all, nop_flush_icache_all
> +
> +       .globl nop_flush_user_cache_range
> +       .equ nop_flush_user_cache_range, nop_flush_icache_all
> +
> +       .globl nop_coherent_kern_range
> +       .equ nop_coherent_kern_range, nop_flush_icache_all
> +
> +ENTRY(nop_coherent_user_range)
> +       mov     r0, 0
> +       mov     pc, lr
> +ENDPROC(nop_coherent_user_range)
> +
> +       .globl nop_flush_kern_dcache_area
> +       .equ nop_flush_kern_dcache_area, nop_flush_icache_all
> +
> +       .globl nop_dma_flush_range
> +       .equ nop_dma_flush_range, nop_flush_icache_all
> +
> +       .globl nop_dma_map_area
> +       .equ nop_dma_map_area, nop_flush_icache_all
> +
> +       .globl nop_dma_unmap_area
> +       .equ nop_dma_unmap_area, nop_flush_icache_all
> +
> +       __INITDATA
> +
> +       @ define struct cpu_cache_fns (see <asm/cacheflush.h> and proc-macros.S)
> +       define_cache_functions nop
> diff --git a/arch/arm/mm/nommu.c b/arch/arm/mm/nommu.c
> index d51225f..4bc8ae5 100644
> --- a/arch/arm/mm/nommu.c
> +++ b/arch/arm/mm/nommu.c
> @@ -20,12 +20,14 @@
>
>   void __init arm_mm_memblock_reserve(void)
>   {
> +#ifndef CONFIG_CPU_V7M

Same deal here about a comment explain V7M's differences
>          /*
>           * Register the exception vector page.
>           * some architectures which the DRAM is the exception vector to trap,
>           * alloc_page breaks with error, although it is not NULL, but "0."
>           */
>          memblock_reserve(CONFIG_VECTORS_BASE, PAGE_SIZE);
> +#endif
>   }
>
>   void __init sanity_check_meminfo(void)
> diff --git a/arch/arm/mm/proc-v7m.S b/arch/arm/mm/proc-v7m.S
> new file mode 100644
> index 0000000..c2b68d3
> --- /dev/null
> +++ b/arch/arm/mm/proc-v7m.S
> @@ -0,0 +1,167 @@
> +/*
> + *  linux/arch/arm/mm/proc-v7m.S
> + *
> + *  Copyright (C) 2008 ARM Ltd.
> + *  Copyright (C) 2001 Deep Blue Solutions Ltd.
> + *
> + * This program is free software; you can redistribute it and/or modify
> + * it under the terms of the GNU General Public License version 2 as
> + * published by the Free Software Foundation.
> + *
> + *  This is the "shell" of the ARMv7-M processor support.
> + */
> +#include <linux/linkage.h>
> +#include <asm/assembler.h>
> +#include <asm/v7m.h>
> +
> +ENTRY(cpu_v7m_proc_init)
> +       mov     pc, lr
> +ENDPROC(cpu_v7m_proc_init)
> +
> +ENTRY(cpu_v7m_proc_fin)
> +       mov     pc, lr
> +ENDPROC(cpu_v7m_proc_fin)
> +
> +/*
> + *     cpu_v7m_reset(loc)
> + *
> + *     Perform a soft reset of the system.  Put the CPU into the
> + *     same state as it would be if it had been reset, and branch
> + *     to what would be the reset vector.
> + *
> + *     - loc   - location to jump to for soft reset
> + */
> +       .align  5
> +ENTRY(cpu_v7m_reset)
> +       mov     pc, r0
> +ENDPROC(cpu_v7m_reset)
> +
> +/*
> + *     cpu_v7m_do_idle()
> + *
> + *     Idle the processor (eg, wait for interrupt).
> + *
> + *     IRQs are already disabled.
> + */
> +ENTRY(cpu_v7m_do_idle)
> +       wfi
> +       mov     pc, lr
> +ENDPROC(cpu_v7m_do_idle)
> +
> +ENTRY(cpu_v7m_dcache_clean_area)
> +       mov     pc, lr
> +ENDPROC(cpu_v7m_dcache_clean_area)
> +
> +/*
> + * There is no MMU, so here is nothing to do.
> + */
> +ENTRY(cpu_v7m_switch_mm)
> +       mov     pc, lr
> +ENDPROC(cpu_v7m_switch_mm)
> +
> +cpu_v7m_name:
> +       .ascii  "ARMv7-M Processor"
> +       .align
> +
> +       .section ".text.init", #alloc, #execinstr
> +
> +/*
> + *     __v7m_setup
> + *
> + *     This should be able to cover all ARMv7-M cores.
> + */
> +__v7m_setup:
> +       @ Configure the vector table base address
> +       ldr     r0, =V7M_SCS_VTOR       @ vector table base address
> +       ldr     r12, =vector_table
> +       str     r12, [r0]
> +
> +       @ enable UsageFault, BusFault and MemManage fault.
> +       ldr     r5, [r0, #(V7M_SCS_SHCSR - V7M_SCS_VTOR)]
> +       orr     r5, #(V7M_SCS_SHCSR_USGFAULTENA | V7M_SCS_SHCSR_BUSFAULTENA | V7M_SCS_SHCSR_MEMFAULTENA)
> +       str     r5, [r0, #(V7M_SCS_SHCSR - V7M_SCS_VTOR)]

This looks weird and is confusing - it makes it seem like there is some 
relationship between SCS_SHCSR and SCS_VTOR, which there isn't at all - 
the only link is that we just loaded SCS_VTOR in to r0 and now we want 
V7M_SCS_SHCSR - right?

Why not do the "ldr r0, =V7M_SCS_SHCS"? Is it to save the one 
instruction? Or save an entry in the literal pool?

I don't think for a single instruction/word it is worth the confusing 
way of writing it...

But then, perhaps I'm missing something?

> +
> +       @ Lower the priority of the SVC and PendSV exceptions
> +       ldr     r0, =V7M_SCS_SHPR2
> +       mov     r5, #0x80000000
> +       str     r5, [r0]                @ set SVC priority
> +       ldr     r0, =V7M_SCS_SHPR3
> +       mov     r5, #0x00800000
> +       str     r5, [r0]                @ set PendSV priority
> +
> +       @ SVC to run the kernel in this mode
> +       adr     r0, BSYM(1f)
> +       ldr     r5, [r12, #11 * 4]      @ read the SVC vector entry
> +       str     r0, [r12, #11 * 4]      @ write the temporary SVC vector entry
> +       mov     r6, lr                  @ save LR
> +       mov     r7, sp                  @ save SP
> +       ldr     sp, =__v7m_setup_stack_top
> +       cpsie   i
> +       svc     #0
> +1:     cpsid   i
> +       str     r5, [r12, #11 * 4]      @ restore the original SVC vector entry
> +       mov     lr, r6                  @ restore LR
> +       mov     sp, r7                  @ restore SP
> +
> +       @ Special-purpose control register
> +       mov     r0, #1
> +       msr     control, r0             @ Thread mode has unpriviledged access
> +
> +       @ Configure the System Control Register

Can we be a bit more specific here?

@Configure the System Control Register to ensure 8-byte stack alignment

> +       ldr     r0, =V7M_SCS_CCR        @ system control register
> +       ldr     r12, [r0]
> +       orr     r12, #V7M_SCS_CCR_STKALIGN

Whether this bit is RO or RW is implementation defined - sorry I didn't 
notice this with earlier responses...

As we always check the stack alignment on exception entry/return I think 
this isn't an issue - but does leave me asking why we bother with this 
if we always do the check?

> +       str     r12, [r0]
> +       mov     pc, lr
> +ENDPROC(__v7m_setup)
> +
> +       .align  2
> +       .type   v7m_processor_functions, #object
> +ENTRY(v7m_processor_functions)
> +       .word   nommu_early_abort
> +       .word   cpu_v7m_proc_init
> +       .word   cpu_v7m_proc_fin
> +       .word   cpu_v7m_reset
> +       .word   cpu_v7m_do_idle
> +       .word   cpu_v7m_dcache_clean_area
> +       .word   cpu_v7m_switch_mm
> +       .word   0                       @ cpu_v7m_set_pte_ext

The fact that we lack a stub function here will mean that compiling with 
module support won't work.

Do you expect modules to work?
If not, can we therefore make V7M and CONFIG_MODULES mutually exclusive.
If so, we should fix this.

> +       .word   legacy_pabort
> +       .size   v7m_processor_functions, . - v7m_processor_functions
> +
> +       .type   cpu_arch_name, #object
> +cpu_arch_name:
> +       .asciz  "armv7m"
> +       .size   cpu_arch_name, . - cpu_arch_name
> +
> +       .type   cpu_elf_name, #object
> +cpu_elf_name:
> +       .asciz  "v7m"
> +       .size   cpu_elf_name, . - cpu_elf_name
> +       .align
> +
> +       .section ".proc.info.init", #alloc, #execinstr
> +
> +       /*
> +        * Match any ARMv7-M processor core.
> +        */
> +       .type   __v7m_proc_info, #object
> +__v7m_proc_info:
> +       .long   0x000f0000              @ Required ID value
> +       .long   0x000f0000              @ Mask for ID
> +       .long   0                       @ proc_info_list.__cpu_mm_mmu_flags
> +       .long   0                       @ proc_info_list.__cpu_io_mmu_flags
> +       b       __v7m_setup             @ proc_info_list.__cpu_flush
> +       .long   cpu_arch_name
> +       .long   cpu_elf_name
> +       .long   HWCAP_SWP|HWCAP_HALF|HWCAP_THUMB|HWCAP_FAST_MULT|HWCAP_EDSP

I don't think M3 has SWP and EDSP...

based on V7M ARMARM:
(For SWP)
"For synchronization, ARMv7-M only supports the byte, halfword, and word 
versions of the load and store exclusive instructions. ARMv7-R also 
supports the doubleword versions of these instructions, and the legacy 
swap instructions"
(For EDSP)
None of the instructions listed as coming from the DSP extensions are 
listed in the M3 TRM (eg PKHTB, SXTAB)

> +       .long   cpu_v7m_name
> +       .long   v7m_processor_functions @ proc_info_list.proc
> +       .long   0                       @ proc_info_list.tlb
> +       .long   0                       @ proc_info_list.user
> +       .long   nop_cache_fns           @ proc_info_list.cache
> +       .size   __v7m_proc_info, . - __v7m_proc_info
> +
> +__v7m_setup_stack:
> +       .space  4 * 8                           @ 8 registers
> +__v7m_setup_stack_top:
> --
> 1.8.2.rc2
>
>

Hope they are useful comments,
Jonny