linux-toradex.git/arch/m68k/kernel/entry.S, branch v4.0.2

m68k: Simplify low level interrupt handling code

2013-11-13T19:21:46+00:00

The low level interrupt entry code of m68k contains the following:

    add_preempt_count(HARDIRQ_OFFSET);

    do_IRQ();
	irq_enter();
	    add_preempt_count(HARDIRQ_OFFSET);
	handle_interrupt();    
	irq_exit();    
	    sub_preempt_count(HARDIRQ_OFFSET);
	    if (in_interrupt())
       	       return; <---- On m68k always taken!
	    if (local_softirq_pending())
       	       do_softirq();

    sub_preempt_count(HARDIRQ_OFFSET);
    if (in_hardirq())
       return;
    if (status_on_stack_has_interrupt_priority_mask > 0)
       return;
    if (local_softirq_pending())
       do_softirq();

    ret_from_exception:
	if (interrupted_context_is_kernel)
	   return:
	....

I tried to find a proper explanation for this, but the changelog is
sparse and there are no mails explaining it further. But obviously
this relates to the interrupt priority levels of the m68k and tries to
be extra clever with nested interrupts. Though this cleverness just
adds code bloat to the interrupt hotpath.

For the common case of non nested interrupts the code runs through two
extra conditionals to the only important one, which checks whether the
return is to kernel or user space.

For the nested case the checks for in_hardirq() and the priority mask
value on stack catch only the case where the nested interrupt happens
inside the hard irq context of the first interrupt. If the nested
interrupt happens while the first interrupt handles soft interrupts,
then these extra checks buy nothing. The nested interrupt will fall
through to the final kernel/user space return check at
ret_from_exception.

Changing the code flow in the following way:

    do_IRQ();
	irq_enter();
	    add_preempt_count(HARDIRQ_OFFSET);
	handle_interrupt();    
	irq_exit();    
	    sub_preempt_count(HARDIRQ_OFFSET);
	    if (in_interrupt())
       	       return;
	    if (local_softirq_pending())
       	       do_softirq();

    ret_from_exception:
	if (interrupted_context_is_kernel)
	   return:

makes the region protected by the hardirq count slightly smaller and
the softirq handling is invoked with a minimal deeper stack. But
otherwise it's completely functional equivalent and saves 104 bytes of
text in arch/m68k/kernel/entry.o.

This modification allows us further to get rid of the limitations
which m68k puts on the preempt_count layout, so we can make the
preempt count bits completely generic.

Signed-off-by: Thomas Gleixner 
Tested-by: Michael Schmitz 
Acked-by: Geert Uytterhoeven 
Cc: Linux/m68k 
Cc: Andreas Schwab 
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1311112052360.30673@ionos.tec.linutronix.de

m68k: sanitize copy_thread(), fork/vfork/clone wrappers, switch to generic fork/vfork

2012-11-29T03:44:46+00:00

Signed-off-by: Al Viro

m68k: switch to saner kernel_execve() semantics

2012-10-17T06:29:27+00:00

Acked-by: Greg Ungerer 
Signed-off-by: Al Viro

m68k: switch to generic sys_execve()/kernel_execve()

2012-10-01T04:44:44+00:00

The tricky part here is that task_pt_regs() on m68k works *only* for
process inside do_signal().  However, we need something much simpler -
pt_regs of a process inside do_signal() may be at different offsets
from the stack bottom, depending on the way we'd entered the kernel,
but for a task inside sys_execve() it *is* at constant offset.
Moreover, for a kernel thread about to become a userland process the
same location is also fine - setting sp to that will leave the kernel
stack pointer at the very bottom of the kernel stack when we finally
switch to userland.

Signed-off-by: Al Viro

m68k: split ret_from_fork(), simplify kernel_thread()

2012-10-01T04:44:44+00:00

Signed-off-by: Al Viro

m68k: merge the MMU and non-MMU versions of the entry.S code

2012-07-15T23:59:21+00:00

Some of the entry.S code is common to both MMU and non-MMU builds.
So merge the entry_no.S and entry_mm.S files back into a single file.
With a little code movement we only need a single #ifdef.

Signed-off-by: Greg Ungerer 
Acked-by: Geert Uytterhoeven

m68k: use non-MMU entry.S code when compiling for ColdFire CPU

2011-12-30T00:20:41+00:00

No matter whether we are configured for non-MMU or MMU enabled if we are
compiling for ColdFire CPU we always use the entry_no.S code.

Signed-off-by: Greg Ungerer 
Acked-by: Geert Uytterhoeven 
Acked-by: Matt Waddel 
Acked-by: Kurt Mahan

m68k: merge m68k and m68knommu arch directories

2011-03-25T04:05:13+00:00

There is a lot of common code that could be shared between the m68k
and m68knommu arch branches. It makes sense to merge the two branches
into a single directory structure so that we can more easily share
that common code.

This is a brute force merge, based on a script from Stephen King
, which was originally written by Arnd Bergmann
.

> The script was inspired by the script Sam Ravnborg used to merge the
> includes from m68knommu. For those files common to both arches but
> differing in content, the m68k version of the file is renamed to
> _mm. and the m68knommu version of the file is moved into the
> corresponding m68k directory and renamed _no. and a small
> wrapper file . is used to select between the two version. Files
> that are common to both but don't differ are removed from the m68knommu
> tree and files and directories that are unique to the m68knommu tree are
> moved to the m68k tree. Finally, the arch/m68knommu tree is removed.
>
> To select between the the versions of the files, the wrapper uses
>
> #ifdef CONFIG_MMU
> #include _mm.
> #else
> #include _no.
> #endif

On top of this file merge I have done a simplistic merge of m68k and
m68knommu Kconfig, which primarily attempts to keep existing options and
menus in place. Other than a handful of options being moved it produces
identical .config outputs on m68k and m68knommu targets I tested it on.

With this in place there is now quite a bit of scope for merge cleanups
in future patches.

Signed-off-by: Greg Ungerer

m68k: Missing syscall_trace() on sigreturn

2011-01-07T13:01:35+00:00

If we leave sigreturn via ret_from_signal, we end up with syscall
trace only on entry, leading to very unhappy strace, among other
things.  Note that this means different behaviours for signals
delivered while we were in pagefault and for ones delivered while
we were in interrupt...

Signed-off-by: Al Viro 
Signed-off-by: Geert Uytterhoeven

m68k: Simplify the singlestepping handling in signals

2011-01-07T13:01:34+00:00

Instead of checking the return value of do_signal() we can just do
the work (raise SIGTRAP and clear SR.T1) directly in handle_signal(),
when setting the sigframe up.  Simplifies the assembler glue and is
closer to the way we do it on other targets.

Note that do_delayed_trace does *not* disappear; it's still needed
to deal with single-stepping through syscall, since 68040 doesn't
raise the trace exception at all if the trap exception is pending.
We hit it after returning from sys_...() if TIF_DELAYED_TRACE is
set; all that has changed is that we don't reuse it for "single-step
into the handler" codepath.

As the result, do_signal() doesn't need to return anything anymore.

Signed-off-by: Al Viro 
Signed-off-by: Geert Uytterhoeven