linux/arch/blackfin/kernel/entry.S
Philippe Gerum 6b8019c85e Blackfin: allow high priority domains to preempt schedule_tail()
ret_from_fork is always entered with hw interrupts off, which prevents
real-time domains to preempt the Linux kernel during part of the
initial context switch to the new task, which could in turn raise the
worst-case latency figures.

To avoid this, stall the root domain stage in the interrupt pipeline
to keep the scheduling tail code free from Linux-handled IRQs, then
enable hardware interrupts again.

Signed-off-by: Philippe Gerum <rpm@xenomai.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>
2009-09-16 21:28:33 -04:00

132 lines
2.8 KiB
ArmAsm

/*
* File: arch/blackfin/kernel/entry.S
* Based on:
* Author:
*
* Created:
* Description:
*
* Modified:
* Copyright 2004-2006 Analog Devices Inc.
*
* Bugs: Enter bugs at http://blackfin.uclinux.org/
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, see the file COPYING, or write
* to the Free Software Foundation, Inc.,
* 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
*/
#include <linux/linkage.h>
#include <asm/thread_info.h>
#include <asm/errno.h>
#include <asm/blackfin.h>
#include <asm/asm-offsets.h>
#include <asm/context.S>
#ifdef CONFIG_EXCPT_IRQ_SYSC_L1
.section .l1.text
#else
.text
#endif
ENTRY(_ret_from_fork)
#ifdef CONFIG_IPIPE
/*
* Hw IRQs are off on entry, and we don't want the scheduling tail
* code to starve high priority domains from interrupts while it
* runs. Therefore we first stall the root stage to have the
* virtual interrupt state reflect IMASK.
*/
p0.l = ___ipipe_root_status;
p0.h = ___ipipe_root_status;
r4 = [p0];
bitset(r4, 0);
[p0] = r4;
/*
* Then we may enable hw IRQs, allowing preemption from high
* priority domains. schedule_tail() will do local_irq_enable()
* since Blackfin does not define __ARCH_WANT_UNLOCKED_CTXSW, so
* there is no need to unstall the root domain by ourselves
* afterwards.
*/
p0.l = _bfin_irq_flags;
p0.h = _bfin_irq_flags;
r4 = [p0];
sti r4;
#endif /* CONFIG_IPIPE */
SP += -12;
call _schedule_tail;
SP += 12;
r0 = [sp + PT_IPEND];
cc = bittst(r0,1);
if cc jump .Lin_kernel;
RESTORE_CONTEXT
rti;
.Lin_kernel:
bitclr(r0,1);
[sp + PT_IPEND] = r0;
/* do a 'fake' RTI by jumping to [RETI]
* to avoid clearing supervisor mode in child
*/
r0 = [sp + PT_PC];
[sp + PT_P0] = r0;
RESTORE_ALL_SYS
jump (p0);
ENDPROC(_ret_from_fork)
ENTRY(_sys_fork)
r0 = -EINVAL;
#if (ANOMALY_05000371)
nop;
nop;
nop;
#endif
rts;
ENDPROC(_sys_fork)
ENTRY(_sys_vfork)
r0 = sp;
r0 += 24;
[--sp] = rets;
SP += -12;
call _bfin_vfork;
SP += 12;
rets = [sp++];
rts;
ENDPROC(_sys_vfork)
ENTRY(_sys_clone)
r0 = sp;
r0 += 24;
[--sp] = rets;
SP += -12;
call _bfin_clone;
SP += 12;
rets = [sp++];
rts;
ENDPROC(_sys_clone)
ENTRY(_sys_rt_sigreturn)
r0 = sp;
r0 += 24;
[--sp] = rets;
SP += -12;
call _do_rt_sigreturn;
SP += 12;
rets = [sp++];
rts;
ENDPROC(_sys_rt_sigreturn)