From d7617452eb27c1054ff67c4c9db4b63053d20125 Mon Sep 17 00:00:00 2001 From: Balaji Rao Date: Sun, 22 Feb 2009 04:39:41 +0000 Subject: fiq_handler_in_c.patch The code for creating FIQ handlers in C is moved to arch/arm/kerne/fiq.c Signed-off-by: Balaji Rao --- arch/arm/kernel/fiq.c | 79 +++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 79 insertions(+) (limited to 'arch/arm/kernel') diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c index 36f81d96797..1307c0fbe66 100644 --- a/arch/arm/kernel/fiq.c +++ b/arch/arm/kernel/fiq.c @@ -8,6 +8,8 @@ * * FIQ support re-written by Russell King to be more generic * + * FIQ handler in C supoprt written by Andy Green + * * We now properly support a method by which the FIQ handlers can * be stacked onto the vector. We still do not support sharing * the FIQ vector itself. @@ -124,6 +126,83 @@ void __attribute__((naked)) get_fiq_regs(struct pt_regs *regs) : "r" (®s->ARM_r8), "I" (PSR_I_BIT | PSR_F_BIT | FIQ_MODE)); } +/* -------- FIQ handler in C --------- + * + * Major Caveats for using this + * --------------------------- + * * + * * 1) it CANNOT touch any vmalloc()'d memory, only memory + * that was kmalloc()'d. Static allocations in the monolithic kernel + * are kmalloc()'d so they are okay. You can touch memory-mapped IO, but + * the pointer for it has to have been stored in kmalloc'd memory. The + * reason for this is simple: every now and then Linux turns off interrupts + * and reorders the paging tables. If a FIQ happens during this time, the + * virtual memory space can be partly or entirely disordered or missing. + * + * 2) Because vmalloc() is used when a module is inserted, THIS FIQ + * ISR HAS TO BE IN THE MONOLITHIC KERNEL, not a module. But the way + * it is set up, you can all to enable and disable it from your module + * and intercommunicate with it through struct fiq_ipc + * fiq_ipc which you can define in + * asm/archfiq_ipc_type.h. The reason is the same as above, a + * FIQ could happen while even the ISR is not present in virtual memory + * space due to pagetables being changed at the time. + * + * 3) You can't call any Linux API code except simple macros + * - understand that FIQ can come in at any time, no matter what + * state of undress the kernel may privately be in, thinking it + * locked the door by turning off interrupts... FIQ is an + * unstoppable monster force (which is its value) + * - they are not vmalloc()'d memory safe + * - they might do crazy stuff like sleep: FIQ pisses fire and + * is not interested in 'sleep' that the weak seem to need + * - calling APIs from FIQ can re-enter un-renterable things + * - summary: you cannot interoperate with linux APIs directly in the FIQ ISR + * + * If you follow these rules, it is fantastic, an extremely powerful, solid, + * genuine hard realtime feature. + */ + +static void (*current_fiq_c_isr)(void); +#define FIQ_C_ISR_STACK_SIZE 256 + +static void __attribute__((naked)) __jump_to_isr(void) +{ + asm __volatile__ ("mov pc, r8"); +} + + +static void __attribute__((naked)) __actual_isr(void) +{ + asm __volatile__ ( + "stmdb sp!, {r0-r12, lr};" + "mov fp, sp;" + ); + + current_fiq_c_isr(); + + asm __volatile__ ( + "ldmia sp!, {r0-r12, lr};" + "subs pc, lr, #4;" + ); +} + +void set_fiq_c_handler(void (*isr)(void)) +{ + struct pt_regs regs; + + memset(®s, 0, sizeof(regs)); + regs.ARM_r8 = (unsigned long) __actual_isr; + regs.ARM_sp = 0xffff001c + FIQ_C_ISR_STACK_SIZE; + + set_fiq_handler(__jump_to_isr, 4); + + current_fiq_c_isr = isr; + + set_fiq_regs(®s); +} +/* -------- FIQ handler in C ---------*/ + int claim_fiq(struct fiq_handler *f) { int ret = 0; -- cgit v1.2.3