[PARISC] Add PREEMPT support

Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

2 files changed, 37 insertions, 8 deletions

diff --git a/arch/parisc/Kconfig b/arch/parisc/Kconfig
index 6b3c50964ca9..2fdf21989dc2 100644
--- a/arch/parisc/Kconfig
+++ b/arch/parisc/Kconfig
@@ -177,14 +177,10 @@ config ARCH_DISCONTIGMEM_DEFAULT
         def_bool y
         depends on ARCH_DISCONTIGMEM_ENABLE
 
+source "kernel/Kconfig.preempt"
 source "kernel/Kconfig.hz"
 source "mm/Kconfig"
 
-config PREEMPT
-        bool
-#       bool "Preemptible Kernel"
-        default n
-
 config COMPAT
         def_bool y
         depends on 64BIT
diff --git a/arch/parisc/kernel/entry.S b/arch/parisc/kernel/entry.S
index 6d17c0a3431b..7c95d7663c29 100644
--- a/arch/parisc/kernel/entry.S
+++ b/arch/parisc/kernel/entry.S
@@ -1014,14 +1014,21 @@ intr_restore:
         nop
         nop
 
+#ifndef CONFIG_PREEMPT
+# define intr_do_preempt        intr_restore
+#endif /* !CONFIG_PREEMPT */
+
         .import schedule,code
 intr_do_resched:
-        /* Only do reschedule if we are returning to user space */
+        /* Only call schedule on return to userspace. If we're returning
+         * to kernel space, we may schedule if CONFIG_PREEMPT, otherwise
+         * we jump back to intr_restore.
+         */
         LDREG   PT_IASQ0(%r16), %r20
-        CMPIB= 0,%r20,intr_restore /* backward */
+        CMPIB=  0, %r20, intr_do_preempt
         nop
         LDREG   PT_IASQ1(%r16), %r20
-        CMPIB= 0,%r20,intr_restore /* backward */
+        CMPIB=  0, %r20, intr_do_preempt
         nop
 
 #ifdef CONFIG_64BIT
@@ -1037,6 +1044,32 @@ intr_do_resched:
 #endif
         ldo     R%intr_check_sig(%r2), %r2
 
+        /* preempt the current task on returning to kernel
+         * mode from an interrupt, iff need_resched is set,
+         * and preempt_count is 0. otherwise, we continue on
+         * our merry way back to the current running task.
+         */
+#ifdef CONFIG_PREEMPT
+        .import preempt_schedule_irq,code
+intr_do_preempt:
+        rsm     PSW_SM_I, %r0           /* disable interrupts */
+
+        /* current_thread_info()->preempt_count */
+        mfctl   %cr30, %r1
+        LDREG   TI_PRE_COUNT(%r1), %r19
+        CMPIB<> 0, %r19, intr_restore   /* if preempt_count > 0 */
+        nop                             /* prev insn branched backwards */
+
+        /* check if we interrupted a critical path */
+        LDREG   PT_PSW(%r16), %r20
+        bb,<,n  %r20, 31 - PSW_SM_I, intr_restore
+        nop
+
+        BL      preempt_schedule_irq, %r2
+        nop
+
+        b       intr_restore            /* ssm PSW_SM_I done by intr_restore */
+#endif /* CONFIG_PREEMPT */
 
         .import do_signal,code
 intr_do_signal: