sh: Add support for 4K stacks.

This enables support for 4K stacks on SH.

Currently this depends on DEBUG_KERNEL, but likely all boards
will switch to this as the default in the future.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>

7 files changed, 170 insertions, 23 deletions

diff --git a/arch/sh/Kconfig.debug b/arch/sh/Kconfig.debug
index f0188e626be0..48479e014dac 100644
--- a/arch/sh/Kconfig.debug
+++ b/arch/sh/Kconfig.debug
@@ -46,6 +46,16 @@ config DEBUG_STACK_USAGE
 
           This option will slow down process creation somewhat.
 
+config 4KSTACKS
+        bool "Use 4Kb for kernel stacks instead of 8Kb"
+        depends on DEBUG_KERNEL
+        help
+          If you say Y here the kernel will use a 4Kb stacksize for the
+          kernel stack attached to each process/thread. This facilitates
+          running more threads on a system and also reduces the pressure
+          on the VM subsystem for higher order allocations. This option
+          will also use IRQ stacks to compensate for the reduced stackspace.
+
 config KGDB
         bool "Include KGDB kernel debugger"
         select FRAME_POINTER
diff --git a/arch/sh/kernel/cpu/irq/ipr.c b/arch/sh/kernel/cpu/irq/ipr.c
index 4c4fd4118d1a..f785822cd5de 100644
--- a/arch/sh/kernel/cpu/irq/ipr.c
+++ b/arch/sh/kernel/cpu/irq/ipr.c
@@ -190,6 +190,8 @@ void __init init_IRQ(void)
         /* Perform the machine specific initialisation */
         if (sh_mv.mv_init_irq != NULL)
                 sh_mv.mv_init_irq();
+
+        irq_ctx_init(smp_processor_id());
 }
 
 #if !defined(CONFIG_CPU_HAS_PINT_IRQ)
diff --git a/arch/sh/kernel/entry.S b/arch/sh/kernel/entry.S
index fd5fe2349f20..fe8221855b28 100644
--- a/arch/sh/kernel/entry.S
+++ b/arch/sh/kernel/entry.S
@@ -716,8 +716,8 @@ ENTRY(handle_exception)
         bt/s    1f              ! It's a kernel to kernel transition.
          mov    r15, k0         ! save original stack to k0
         /* User space to kernel */
-        mov     #0x20, k1
-        shll8   k1              ! k1 := 8192 (== THREAD_SIZE)
+        mov     #(THREAD_SIZE >> 8), k1
+        shll8   k1              ! k1 := THREAD_SIZE
         add     current, k1
         mov     k1, r15         ! change to kernel stack
         !
diff --git a/arch/sh/kernel/head.S b/arch/sh/kernel/head.S
index 3e7d00b7985a..f5f53d14f245 100644
--- a/arch/sh/kernel/head.S
+++ b/arch/sh/kernel/head.S
@@ -12,7 +12,6 @@
  */
 #include <linux/linkage.h>
 #include <asm/thread_info.h>
-#include <asm/page.h>
 
 #ifdef CONFIG_CPU_SH4A
 #define SYNCO()         synco
@@ -69,8 +68,8 @@ ENTRY(_stext)
         !
         mov.l   2f, r0
         mov     r0, r15         ! Set initial r15 (stack pointer)
-        mov     #0x20, r1       !
-        shll8   r1              ! r1 = 8192
+        mov     #(THREAD_SIZE >> 8), r1
+        shll8   r1              ! r1 = THREAD_SIZE
         sub     r1, r0          !
         ldc     r0, r7_bank     ! ... and initial thread_info
 
diff --git a/arch/sh/kernel/irq.c b/arch/sh/kernel/irq.c
index 7066611aeb72..c7ebd6aec951 100644
--- a/arch/sh/kernel/irq.c
+++ b/arch/sh/kernel/irq.c
@@ -1,5 +1,4 @@
-/* $Id: irq.c,v 1.20 2004/01/13 05:52:11 kkojima Exp $
- *
+/*
  * linux/arch/sh/kernel/irq.c
  *
  *      Copyright (C) 1992, 1998 Linus Torvalds, Ingo Molnar
@@ -7,13 +6,15 @@
  *
  * SuperH version:  Copyright (C) 1999  Niibe Yutaka
  */
-
 #include <linux/irq.h>
 #include <linux/interrupt.h>
+#include <linux/module.h>
 #include <linux/kernel_stat.h>
 #include <linux/seq_file.h>
 #include <asm/irq.h>
 #include <asm/processor.h>
+#include <asm/uaccess.h>
+#include <asm/thread_info.h>
 #include <asm/cpu/mmu_context.h>
 
 /*
@@ -60,11 +61,27 @@ unlock:
 }
 #endif
 
+#ifdef CONFIG_4KSTACKS
+/*
+ * per-CPU IRQ handling contexts (thread information and stack)
+ */
+union irq_ctx {
+        struct thread_info      tinfo;
+        u32                     stack[THREAD_SIZE/sizeof(u32)];
+};
+
+static union irq_ctx *hardirq_ctx[NR_CPUS];
+static union irq_ctx *softirq_ctx[NR_CPUS];
+#endif
+
 asmlinkage int do_IRQ(unsigned long r4, unsigned long r5,
                       unsigned long r6, unsigned long r7,
                       struct pt_regs regs)
 {
         int irq = r4;
+#ifdef CONFIG_4KSTACKS
+        union irq_ctx *curctx, *irqctx;
+#endif
 
         irq_enter();
 
@@ -102,7 +119,135 @@ asmlinkage int do_IRQ(unsigned long r4, unsigned long r5,
 #endif
 
         irq = irq_demux(irq);
-        __do_IRQ(irq, &regs);
+
+#ifdef CONFIG_4KSTACKS
+        curctx = (union irq_ctx *)current_thread_info();
+        irqctx = hardirq_ctx[smp_processor_id()];
+
+        /*
+         * this is where we switch to the IRQ stack. However, if we are
+         * already using the IRQ stack (because we interrupted a hardirq
+         * handler) we can't do that and just have to keep using the
+         * current stack (which is the irq stack already after all)
+         */
+        if (curctx != irqctx) {
+                u32 *isp;
+
+                isp = (u32 *)((char *)irqctx + sizeof(*irqctx));
+                irqctx->tinfo.task = curctx->tinfo.task;
+                irqctx->tinfo.previous_sp = current_stack_pointer;
+
+                __asm__ __volatile__ (
+                        "mov    %0, r4          \n"
+                        "mov    %1, r5          \n"
+                        "mov    r15, r9         \n"
+                        "jsr    @%2             \n"
+                        /* swith to the irq stack */
+                        " mov   %3, r15         \n"
+                        /* restore the stack (ring zero) */
+                        "mov    r9, r15         \n"
+                        : /* no outputs */
+                        : "r" (irq), "r" (&regs), "r" (__do_IRQ), "r" (isp)
+                        /* XXX: A somewhat excessive clobber list? -PFM */
+                        : "memory", "r0", "r1", "r2", "r3", "r4",
+                          "r5", "r6", "r7", "r8", "t", "pr"
+                );
+        } else
+#endif
+                __do_IRQ(irq, &regs);
+
         irq_exit();
+
         return 1;
 }
+
+#ifdef CONFIG_4KSTACKS
+/*
+ * These should really be __section__(".bss.page_aligned") as well, but
+ * gcc's 3.0 and earlier don't handle that correctly.
+ */
+static char softirq_stack[NR_CPUS * THREAD_SIZE]
+                __attribute__((__aligned__(THREAD_SIZE)));
+
+static char hardirq_stack[NR_CPUS * THREAD_SIZE]
+                __attribute__((__aligned__(THREAD_SIZE)));
+
+/*
+ * allocate per-cpu stacks for hardirq and for softirq processing
+ */
+void irq_ctx_init(int cpu)
+{
+        union irq_ctx *irqctx;
+
+        if (hardirq_ctx[cpu])
+                return;
+
+        irqctx = (union irq_ctx *)&hardirq_stack[cpu * THREAD_SIZE];
+        irqctx->tinfo.task              = NULL;
+        irqctx->tinfo.exec_domain       = NULL;
+        irqctx->tinfo.cpu               = cpu;
+        irqctx->tinfo.preempt_count     = HARDIRQ_OFFSET;
+        irqctx->tinfo.addr_limit        = MAKE_MM_SEG(0);
+
+        hardirq_ctx[cpu] = irqctx;
+
+        irqctx = (union irq_ctx *)&softirq_stack[cpu * THREAD_SIZE];
+        irqctx->tinfo.task              = NULL;
+        irqctx->tinfo.exec_domain       = NULL;
+        irqctx->tinfo.cpu               = cpu;
+        irqctx->tinfo.preempt_count     = SOFTIRQ_OFFSET;
+        irqctx->tinfo.addr_limit        = MAKE_MM_SEG(0);
+
+        softirq_ctx[cpu] = irqctx;
+
+        printk("CPU %u irqstacks, hard=%p soft=%p\n",
+                cpu, hardirq_ctx[cpu], softirq_ctx[cpu]);
+}
+
+void irq_ctx_exit(int cpu)
+{
+        hardirq_ctx[cpu] = NULL;
+}
+
+extern asmlinkage void __do_softirq(void);
+
+asmlinkage void do_softirq(void)
+{
+        unsigned long flags;
+        struct thread_info *curctx;
+        union irq_ctx *irqctx;
+        u32 *isp;
+
+        if (in_interrupt())
+                return;
+
+        local_irq_save(flags);
+
+        if (local_softirq_pending()) {
+                curctx = current_thread_info();
+                irqctx = softirq_ctx[smp_processor_id()];
+                irqctx->tinfo.task = curctx->task;
+                irqctx->tinfo.previous_sp = current_stack_pointer;
+
+                /* build the stack frame on the softirq stack */
+                isp = (u32 *)((char *)irqctx + sizeof(*irqctx));
+
+                __asm__ __volatile__ (
+                        "mov    r15, r9         \n"
+                        "jsr    @%0             \n"
+                        /* switch to the softirq stack */
+                        " mov   %1, r15         \n"
+                        /* restore the thread stack */
+                        "mov    r9, r15         \n"
+                        : /* no outputs */
+                        : "r" (__do_softirq), "r" (isp)
+                        /* XXX: A somewhat excessive clobber list? -PFM */
+                        : "memory", "r0", "r1", "r2", "r3", "r4",
+                          "r5", "r6", "r7", "r8", "r9", "r15", "t", "pr"
+                );
+        }
+
+        local_irq_restore(flags);
+}
+EXPORT_SYMBOL(do_softirq);
+#endif
diff --git a/arch/sh/kernel/traps.c b/arch/sh/kernel/traps.c
index 95c810b3c97e..c2c597e09482 100644
--- a/arch/sh/kernel/traps.c
+++ b/arch/sh/kernel/traps.c
@@ -741,20 +741,12 @@ void show_stack(struct task_struct *tsk, unsigned long *sp)
         unsigned long module_end = VMALLOC_END;
         int i = 1;
 
-        if (tsk && !sp) {
+        if (!tsk)
+                tsk = current;
+        if (tsk == current)
+                sp = (unsigned long *)current_stack_pointer;
+        else
                 sp = (unsigned long *)tsk->thread.sp;
-        }
-
-        if (!sp) {
-                __asm__ __volatile__ (
-                        "mov r15, %0\n\t"
-                        "stc r7_bank, %1\n\t"
-                        : "=r" (module_start),
-                          "=r" (module_end)
-                );
-                
-                sp = (unsigned long *)module_start;
-        }
 
         stack = sp;
 
diff --git a/arch/sh/kernel/vmlinux.lds.S b/arch/sh/kernel/vmlinux.lds.S
index 0220d8a838a7..5eb930918186 100644
--- a/arch/sh/kernel/vmlinux.lds.S
+++ b/arch/sh/kernel/vmlinux.lds.S
@@ -3,7 +3,6 @@
  * Written by Niibe Yutaka
  */
 #include <asm/thread_info.h>
-#include <asm/page.h>
 #include <asm-generic/vmlinux.lds.h>
 
 #ifdef CONFIG_CPU_LITTLE_ENDIAN